essay analogy example

What is an Analogy? Explained With 10 Top Examples

What is an analogy? Read our guide with top examples and in-depth explanations so you can wrap your head around this literary device.

Literary devices make your prose more colorful and vivid, allowing the reader to make associations. What is an analogy? An analogy compares two seemingly unlike things to help draw a conclusion by highlighting their similarities. Unlike other comparisons, like similes and metaphors, an analogy gives more detail about the comparison to help the reader understand it better. 

While there are many different types of analogy to study, the best way to understand this and other figures of speech is to consider examples. After reading a few analogies, you will be better equipped to spot them or write your own. And when you have finished here, check out our comparison article, simile vs metaphor .

What is An Analogy?

What are the benefits of using an analogy, analogy examples, 1. a name is a rose from romeo and juliet, 2. life is a shadow from macbeth, 3. the crowd is like a fisherman in “a hanging”, 4. life is like a box of chocolates from forrest gump, 5. pulling out troops is like salted peanuts from henry kissinger, 6. the futility of a new author from cocktail time, 7. the mystery of life in let me count the ways, 8. the push for freedom is like summer’s heat in “i have a dream”, 9. a needle in a haystack, 10. rearranging deck chairs on the titanic, 11. the matrix’s pill analogy, 12. harry potter and the sorcerer’s stone, what is the opposite of an analogy, what is an example of an analogy, what is the simple definition of analogy, what are 5 examples of analogy, what is another word for an analogy.

An analogy compares two concepts, usually to explain or clarify an idea. Writers use analogies to help people understand complex or abstract topics by relating something abstract to the familiar or concrete. They also use them as a type of literary device to improve the readability of their works.

By highlighting similarities, a writer helps readers see how one thing works or behaves by comparing the characteristics of abstract ideas to more familiar ideas. As a result, a concept or idea becomes easier to understand and even more memorable.

For example, a news reporter could employ this word analogy: “The presidential race for 2024 is like a chessboard…” Teachers use different types of analogies to demonstrate a concept to a student. For this reason, analogy tests often form part of standardized tests in any good English curriculum.

Analogies work in the real world too! For example, if a running coach wants to explain how a runner can run faster, they could use an analogy like “Pump your arms like a train” to help people understand how they should use their arms and legs to run faster. You might also be interested in learning  what is tautology .

Examples of analogies exist in classic literature, the latest books, movies and TV shows. Here are a few:

Often, analogies compare abstract concepts to something you can touch and feel. There are several examples of analogy in William Shakespeare’s Romeo and Juliet. In this analogy, the playwright compares someone’s name to a rose. The rose retains its sweet smell no matter how it is named, as does the person, regardless of his name. Read our guide to the best books of classic literature .

“If you want my final opinion on the mystery of life and all that, I can give it to you in a nutshell. The universe is like a safe to which there is a combination. But the combination is locked up in the safe.”

Life is a difficult concept to understand, making it a favorite topic for people who write analogies. In Act V of Macbeth, Shakespeare creates an analogy example by comparing a person’s life, and its brevity, to a fleeting shadow:

“Life’s but a walking shadow, a poor player That struts and frets his hour upon the stage And then is heard no more. It is a tale  Told by an idiot, full of sound and fury, Signifying nothing.”

Because life is so fleeting, this analogy works. The reader can see the shadow flitting about on the stage, then disappearing, reminding the reader how short life really is. You might also find these  headings and subheadings examples  helpful.

Some analogies take a little more time to explain yet still compare unlike things to make a point. For example, in his essay entitled  A Hanging  George Orwell describes the crowd gripping a man as they lead him to the gallows. The analogy is the comparison to the way a man would hold a slippery fish:

“They crowded very close about him, with their hands always on him in a careful, caressing grip, as though all the while feeling him to make sure he was there. It was like men handling a fish which is still alive and may jump back into the water. But he stood quite unresisting, yielding his arms limply to the ropes, as though he hardly noticed what was happening.”

This analogy is also an example of a simile because it uses the word “like” to make the comparison. However, because it extends beyond just one statement but has a complete description and explanation, it brings more imagery to the reader’s mind and thus is an analogy. Read our guide to the  best satirical authors .

Some analogies are short and sweet, rather than taking up an entire literary work. In the movie Forrest Gump, both the title character and his mother refer to life as a “box of chocolates.” In one of the most famous figures of speech from this movie, Forest says:

“My mom always said life was like a box of chocolates. You never know what you’re gonna get.”

Though this is a simple statement, it is an example of an analogy. The reader has probably experienced the feeling of grabbing chocolate and wondering what flavor it is, so this is a good analogy. But, like life, that box of chocolates always has the potential to give you the unexpected. You might also be wondering,  what is point of view?

Though technically a historian and not a literary genius, Henry Kissinger was famous for many of his analogies. One of his most commonly quoted is this:

“Withdrawal of U.S. troops will become like salted peanuts to the American public; the more U.S. troops come home, the more will be demanded. This could eventually result, in effect, in demands for unilateral withdrawal.”

This quote comes from a  memorandum Kissinger sent to President Nixon  regarding the conflict in Vietnam. He warned the president that bringing troops home a little at a time would create demand for more withdrawal, just like eating tasty peanuts makes you want to eat more. 

Writing a book is definitely challenging, especially when doing so for the first time. This fact is the source of one famous analogy in literature. In  Cocktail Time , P.G. Wodehouse compares a new author to someone performing an impossible task:

“It has been well said that an author who expects results from a first novel is in a position similar to that of a man who drops a rose petal down the Grand Canyon of Arizona and listens for the echo.”

Clearly, expecting to hear an echo from a rose petal at the Grand Canyon is foolishness. Thus, based on this analogy, the logical argument that expecting to see significant returns from a first novel is also foolish. You might also be wondering  what is a split infinitive .

In his novel  Let Me Count the Ways , Dutch author and journalist  Peter De Vries  compares life and a safe. He writes:

In this analogy, the safe can’t be unlocked. Similarly, the mystery of life is something people can’t fully understand.

Speechwriters who are good at their jobs often use analogies to make their words more memorable. In his famous speech, “I Have a Dream,” Martin Luther King, Jr., makes an analogy between the anger of African-Americans and the heat of summer in this quote:

“This sweltering summer of the Negro’s legitimate discontent will not pass until there is an invigorating autumn of freedom and equality.”

Just like the heat of summer is unquenchable, the frustration of those facing endless prejudice cannot be quenched. Yet when freedom comes, it is like the relief of the cool autumn breeze. This quote is still used today when people remember the famous civil rights activist.

Finding a needle in a haystack is a nearly impossible task. This catchphrase or analogy example is often applied to tasks that seem out of reach. For instance, one common analogy says:

“Finding a good man is as easy as finding a needle in a haystack.”

This analogy indicates it is nearly impossible to find a “good man.” Though unfair to the male gender, it does make its point through the use of analogy. Most people can picture digging through the hay to find a needle, but to no avail, which makes the analogy work.

This analogy does not come from any famous literary work or speech but from a well-known historical moment. The sinking of the Titanic was one such event. Sometimes people, when talking about something futile, will say:

“That’s as useful as rearranging deck chairs on the Titanic.”

Since the Titanic was a doomed vessel, the futility of the effort is seen in this use of figurative language. The phrase can apply to any effort that would not matter because the result is a failure, like the sinking of the infamous ship. Check out our metonymy examples .

In The Matrix , there is a famous scene where Morpheus presents the red pill/blue pill analogy to Neo. The analogy is a turning point in the movie where Neo has to pick which path he wants to go down. The red pill represents embracing the uncomfortable truth and becoming aware of the real world he lives in. The blue pill represents choosing the familiar and comfortable path where he can remain in his world, oblivious to the dark reality he suspects.

“You take the blue pill, the story ends. You wake up in your bed and believe whatever you want to believe. You take the red pill, you stay in Wonderland, and I show you how deep the rabbit hole goes.”

J.K. Rowling uses analogies throughout her works, often to give insight into the minds and personalities of the characters. In Harry Potter and the Sorcerer’s Stone , Professor Dumbledore speaks to Harry and imparts some of his famous wisdom.

“It does not do to dwell on dreams and forget to live.”

In this analogy example sentence, he suggests that while having dreams and aspirations are important, it’s just as important to be grounded and present in the current moment. The analogy aims to show Harry that he should balance his ambition and reality and become mindful in the midst of the chaos that he lives in. It also encourages Harry to let go of regrets and become fully present in his life as it is today.

An antithesis highlights the differences between two contrasting ideas. For example, the analogy “Man plans, and God laughs” shows how we can strive and work towards a goal, only for God or fate to intervene and uproot our best plans. For further reading on a similar subject, check out our post on examples of metaphors in literature .

FAQs About What is an Analogy

An example of an analogy is “Hope is the lighthouse that stands tall amidst the stormy seas of despair.” The analogy emphasizes the idea that hope can help us navigate through the storms of life, guiding us toward a better future and helping us persevere in the face of challenges.

An analogy is a comparison between two things that are alike in some way, often used to help explain something or make it easier to understand.

1. Her laughter was music to his ears. 2. Time is money. 3. He is a shining star in the world of science. 4. The classroom was a zoo during the group activity. 5. Life is a journey with its share of twists and turns.

A related term for analogy is comparison. A comparison is a way of describing the similarities or differences between two things in order to better understand them.

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Definition of Analogy

An analogy is a figure of speech that creates a comparison by showing how two seemingly different entities are alike, along with illustrating a larger point due to their commonalities. As a literary device, the purpose of analogy is not just to make a comparison, but to provide an explanation as well with additional information or context . This makes analogy a bit more complex than similar literary devices such as metaphor and simile . Analogy is an effective device in terms of providing a new or deeper meaning to concepts through the artistic use of language.

For example, the analogy  nose is to olfactory as ear is to auditory makes a comparison between parts of the body that are related to certain senses and the words to describe the senses themselves. “Olfactory” refers to the sense of smell, which is related to “nose.” “Auditory” refers to the sense of hearing, which is related to “ear.” Of course, the writer could use the analogy  nose is to smell as ear is to hear for a similar comparison. However, the description words of olfactory and auditory create a deeper meaning and sense of the relationship between these parts of the body and the senses.

Common Examples of Analogy

Many people are introduced to analogy as a form of word relationship that demonstrates the associations between two object or concept pairs on the basis of logic or reasoning. The phrasing for these analogies is generally “(first word) is to (second word) as (third word) is to (fourth word)” or “baby is to adult as kitten is to cat.” Here are some common examples of verbal analogies:

• blue is to color as circle is to shape
• eyes are to sight as fingers are to touch
• cub is to bear and calf is to cow
• sand is to beach as water is to ocean
• glove is to hand as sock is to foot
• ripple is to pond as wave is to ocean
• words are to writing as notes are to music
• fish are to aquariums as animals are to zoos
• fingers are to snapping as hands are to clapping
• petal is to flower as leaf is to tree

Famous Examples of Analogy

Think you haven’t heard of any famous analogies? Here are some recognizable examples of this figure of speech by well-known writers and speakers :

• That which we call a rose / By any other name would smell as sweet ( William Shakespeare )
• And I began to let him go. Hour by hour. Days into months. It was a physical sensation, like letting out the string of a kite. Except that the string was coming from my center. (Augusten Burroughs)
• It has been well said that an author who expects results from a first novel is in a position similar to that of a man who drops a rose petal down the Grand Canyon of Arizona and listens for the echo. (P.G. Wodehouse)
• Don’t worry about the future. Or worry, but know that worrying is as effective as trying to solve an algebra equation by chewing bubble gum. (Mary Schmich)
• Confession is good for the soul only in the sense that a tweed coat is good for dandruff – it is a palliative rather than a remedy. (Peter De Vries)
• Withdrawal of U.S. troops will become like salted peanuts to the American public; the more U.S. troops come home, the more will be demanded. (Henry Kissinger)
• People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is a light from within. (Elisabeth Kubler-Ross)
• A nation wearing atomic armor is like a knight whose armor has grown so heavy he is immobilized; he can hardly walk, hardly sit his horse, hardly think, hardly breathe. The H-bomb is an extremely effective deterrent to war, but it has little virtue as a weapon of war because it would leave the world uninhabitable. (E.B. White)

Examples of Analogy by Thomas Carlyle

Thomas Carlyle was a British writer, historian, philosopher, and mathematician of the 19th Century. His writings often featured analogies that have since appeared in standardized tests of advanced placement English, among others. Carlyle’s analogies are thought-provoking as comparisons and valuable for analysis. Here are some examples:

• Under all speech that is good for anything, there lies a silence that is better. Silence is deep as Eternity; speech is shallow as Time.
• No great man lives in vain. The history of the world is but the biography of great men.
• It has been well said that the highest aim in education is analogous to the highest aim in mathematics, namely, to obtain not results but powers, not particular solutions, but the means by which endless solutions may be wrought.
• What we become depends on what we read after all of the professors have finished with us. The greatest university of all is a collection of books.
• Music is well said to be the speech of angels; in fact, nothing among the utterances allowed to man is felt to be so divine. It brings us near to the infinite.
• The block of granite which was an obstacle in the pathway of the weak becomes a stepping-stone in the pathway of the strong.
• Wondrous is the strength of cheerfulness, and its power of endurance – the cheerful man will do more in the same time, will do it better, will preserve it longer, than the sad or sullen.
• Show me the man you honor, and I will know what kind of man you are.

Difference Between Analogy, Metaphor, and Simile

Analogies, similes, and metaphors are all figures of speech used to create comparisons between different entities. These literary devices are often confused with each other, though they can be distinguished. A simile utilizes the words “like” or “as” to make a comparison. A metaphor uses figurative language to compare two things by stating that one is the other. An analogy creates a comparison with the intent of explanation or indicating a larger point.

Here are some examples to help differentiate between these three literary devices:

• Memory is to love what the saucer is to the cup.– This is an analogy . It explains the abstract relationship between memory and love by making a comparison between the tangible and familiar relationship between a cup and saucer. Though these entities are different in terms of abstract concepts and tangible items, they are alike in the sense that a saucer holds and supports a cup as memory holds and supports love. This analogy provides an interesting image of the relationship between memory and love through the artistic comparison to the saucer and cup.
• Memory and love are like a saucer and cup. –This figure of speech is a Simile . The presence of the word “like” is the basis of the comparison.
• Memory and love are a saucer and cup. –This is an example of a Metaphor . The language used in this metaphor is figurative in the sense that the reader knows that memory and love are not literally a saucer and cup. Instead, the example is making a comparison by linking them directly–that one is the other.

Analogy, simile, and metaphor are all useful and related literary devices for writers to make comparisons. The intention of these devices and their wording is what differentiates them from each other.

Writing Analogy

Overall, as a literary device, analogy functions as a means of comparing entities and enhancing the clarity of one entity through connection with the other. This is effective for readers in that analogies create imagery and a deeper understanding of concepts. Therefore, this can enhance the meaning and understanding of a literary work or theme by using artistic language to present ideas in a new way.

There are two primary types of analogy:

• Identification of identical relationships: Like the word relationships featured above, Greek scholars utilized analogies as direct illustrations of similar relationships between word pairings. These analogies identify identical word relationships based in logic and for the purpose of reasoned argument . They also enhance connections for readers between the meanings of words and concepts.
• Identification of shared abstraction: This type of analogy creates comparisons between two things that appear unrelated but share an attribute or pattern. The purpose of these analogies is to utilize a reader’s current knowledge of something familiar and connect it to an abstract idea so that it is more concrete in comparison.

Writers benefit from incorporating analogies into their work for the purpose of explaining and connecting ideas for their readers. It’s important for writers to understand that an effective analogy is one in which the comparison is logical and easily understood. An analogy that made an unreasonable or illogical comparison would be an improper use of the literary device.

Types of Analogy: Literal and Figurative

There are two types of analogy. One is literal and the other is figurative. In literal analogy, the comparison is literal, as one thing is stated to be similar to the other. It is used for persuasion in an argument. However, the figurative analogy is based on some features and properties. It mostly occurs through metaphors and similes. Both of these figures of speech are used in figurative analogies.

Types of Analogy in Writing

Analogy occurs at two levels in writing. The first one is the comparison of relationships. Two things are set side by side and their relationship is identified through the use of similes. The second analogical writing is about abstract ideas as two ideas are compared with each other by setting them side by side.

Use of Analogy in Sentences

• Searching for a chicken in Granma’s soup is like searching for a turtle in the ocean.
• Abbie’s like a squeaky mouse when she’s on the stage.
• Water is to the lake as lava is to the volcano.
• Pedals are to the bicycle as oars are to the boat.
• Flow is for water as the break is for solid.
• Drive : Steer :: Live : Breathe (A few analogies used for critical thinking are written in this form)

Examples of Analogy in Literature

Analogy is an effective literary device as a method of creating comparisons and developing meaning. Here are some examples of analogy and the way it enhances the significance of well-known literary works:

Example 1: There is no Frigate like a Book by Emily Dickinson

There is No Frigate like a Book To take us Lands away Nor any Coursers like a Page Of prancing Poetry – This Traverse may the poorest take Without oppress of Toll – How frugal is the Chariot That bears the Human Soul –

Example 2: Do Not Go Gentle Into That Good Night by Dylan Thomas

Grave men, near death, who see with blinding sight Blind eyes could blaze like meteors and be gay, Rage, rage against the dying of the light.

In this stanza , Thomas utilizes several literary devices, including metaphor and simile. As a whole, these lines create an analogy for death. “The dying of the light” signifies death, and that moment is compared to both blindness and sight. This creates a deeper meaning as the poet calls for “rage” against this moment to fight against blindness towards the unknown and the clarity of vision that comes with death.

Example 3: A Week on the Concord and Merrimack Rivers by Henry David Thoreau

This world is but a canvas to our imaginations.

In this analogy, Thoreau compares the world to a canvas in terms of human imagination. To a degree, Thoreau could have created a more abstract comparison by stating that the world is but a canvas, which would have implied creativity, art, beauty in nature, and so on. Instead, he provides the added context of imagination. This allows for clarity as to what Thoreau is trying to convey to his readers, yet the analogy is still comprised of artistic and figurative language.

Synonyms of Analogy

Like other literary devices, it has close synonyms such as likeness, similarity, resemblance, or similitude could prove its synonyms.

Related posts:

• Importance of Analogy and How to Write with Examples

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Analogy Definition

What is an analogy? Here’s a quick and simple definition:

An analogy is a comparison that aims to explain a thing or idea by likening it to something else. For example, a career coach might say, "Being the successful boss or CEO of a company is like being an orchestra conductor: just as the conductor needs to stand up front where everyone— even the musicians in the back row—can see him, a good CEO needs to make sure he or she is visible and available to all of the company's employees." The career coach is not saying that CEOs are exactly like orchestra conductors in every way. Rather, comparing CEOs to conductors through analogy allows the coach to articulate an important leadership quality in a memorable way.

Some additional key details about analogies:

• Analogy has different meanings in the context of different academic fields. For instance, someone studying logic would say that analogy is "an inference that, if two things are similar in some ways, they must also be alike in others." A cognitive scientist or a lawyer would have a different definition altogether. Despite the term's broad usage, this guide will focus solely on the literary definition of analogy summarized above.
• Analogy is closely related to metaphor and simile . Sources vary in how they define the relationship between these terms, but most can agree that metaphor and simile are types of analogy.

Analogy Pronunciation

Here's how to pronounce analogy: uh- nal -oh-jee

Analogy Explained

Developing a richer understanding of one thing by comparing it to another is the basic idea behind analogy. Far more than simply an illustrative or explanatory technique, analogies are fundamental to the way people think. The writer Douglas Hofstadter even went so far as to say that analogy is "the core of cognition," suggesting that the most fundamental tool we have for understanding the world is the ability to make comparisons between things.

What Makes an Analogy

Analogies can be broken down into two elements: the target and the source . The target is the unknown concept—the thing that the analogy seeks to explain—while the source (also referred to as the analog ) is the known concept, or the thing used to explain the target.

For example, if you've ever seen the Disney movie Shrek , you may remember the phrase "ogres are like onions." In a memorable scene, the ogre (Shrek) tries to explain something about the true nature of ogres to his non-ogre friend by saying:

"Ogres are like onions... Onions have layers. Ogres have layers. You get it? We both have layers."

Shrek creates an analogy comparing the source (something familiar and known, in this case an onion) to the target (something mysterious and unknown, in this case ogres). His goal is to reveal something about ogres (the unfamiliar target ) by showing that he's not so different from onions (the familiar source ) . Not all analogies are as cut-and-dry as this one, but Shrek's comparison is a good example of the basic structure of analogies. Keep in mind, it's perfectly acceptable to analyze analogies without talking about targets and sources—but these terms can be helpful in understanding the structure of analogies, especially with more complicated examples.

Analogy, Metaphor, and Simile

Analogy, metaphor and simile are all similar in that they all have to do with making comparisons. But there's some debate about the precise nature of the relationship between these three concepts. There are two main camps in this debate:

• The first camp believes that metaphor and simile are types of analogies.
• The second camp believes that metaphor and simile are not types of analogies, but distinct tools that can be used to articulate analogy.

Camp 1: Metaphors and Similes are Types of Analogies

Members of this camp see analogies as a broader category into which metaphors and similes fit. They would say that metaphors are implicit analogies, while similes are explicit analogies. In other words, metaphors implicitly perform the function of analogy—pointing out similarities between two different things—by saying that something is something else. For example, "Juliet is the sun." People in the first camp would argue that the metaphor "Juliet is the sun" is a type of analogy because it operates by making an implicit comparison, such as "Juliet and the sun are similar; just like the sun, Juliet is radiant and fills Romeo's days with light." Meanwhile, first-campers would say that the simile "Juliet is like the sun" is also a type of analogy because it draws a comparison explicitly by saying that something is like something else in some respect: "Juliet is beautiful like the sun."

Camp 2: Metaphors and Similes are Tools for Making Analogies

The second camp, however, would say that the metaphor "Juliet is the sun" does not count as analogy. Instead, they would say that the metaphor is being used as a tool to support the distinct and overarching analogy between a woman and the sun. Similarly, second-campers would say that the sentence "Juliet is beautiful like the sun" is a simile which supports the overall analogy comparing Juliet to a celestial body.

The second camp argues that analogy is distinct from metaphors and similes. It argues that analogy is a rational type of argument or explanation—that analogy is the actual conceptual comparison being made. In contrast, it argues that metaphor and simile are figures of speech —that is, they are literary devices or tools whose purpose is to describe something with figurative language rather than to explain or argue something.

However, this distinction can start to seem fuzzy when you start to ask where "describing" ends and "explaining" begins. When Romeo says that "Juliet is the sun," isn't he—in addition to describing her beauty— e xplaining to the reader his love for Juliet by comparing it to the sun?

Summing up the Camp 1 and Camp 2 Debate

It's not necessarily the case that one camp's view is better or more proper than the other, but the first camp's definition of the relationship between analogy, metaphor, and simile is more common—if only because it's not as rigid as the second camp's definition. That said, you only need to know that there are these competing definitions, and then be able to say why you think a given example is an analogy, simile, or metaphor based on the definition you think best fits each term.

Analogy Examples

Analogy in shakespeare's romeo and juliet.

In this example from Act 2 Scene 2 of Romeo and Juliet , Juliet Capulet puzzles over the main obstacle in her love for Romeo Montague: the Capulet and Montague families are rivals. She creates an analogy comparing Romeo to a rose, reasoning that just as the "sweetness" or loveliness of a rose is entirely independent of its name, the "perfection" she sees in Romeo is independent of—and not at all compromised by— his name and family:

’Tis but thy name that is my enemy. Thou art thyself, though not a Montague. What’s Montague? It is nor hand, nor foot, Nor arm, nor face, nor any other part Belonging to a man. O, be some other name! What’s in a name? That which we call a rose By any other word would smell as sweet. So Romeo would, were he not Romeo call’d, Retain that dear perfection which he owes Without that title.

Analogy in Shakespeare's As You Like It

The melancholy character Jaques crafts the following analogy in Act 2 Scene 7 of As You Like It . In one of the most famous lines from all of Shakespeare, Jaques compares the world to stage, and each individual to an actor playing a part that changes with age.

All the world's a stage, And all the men and women merely players; They have their exits and their entrances, And one man in his time plays many parts, His acts being seven ages. At first, the infant, Mewling and puking in the nurse's arms. Then the whining schoolboy, with his satchel And shining morning face, creeping like snail Unwillingly to school. And then the lover, Sighing like furnace, with a woeful ballad Made to his mistress' eyebrow. Then a soldier, Full of strange oaths and bearded like the pard, Jealous in honor, sudden and quick in quarrel, Seeking the bubble reputation Even in the cannon's mouth...

Jaques concludes his speech by describing the remaining three "parts" or "seven ages": those of the Just Leader, The Silly Old Man who thinks he's still young, and the Truly Old Man who's as helpless as a baby. Using this analogy to compare "the world" to "a stage," and by extension "life" to "a play," allows Jaques to point out what he sees as a fundamental aspect of both real and theatrical experience: performance. These lines function as a particularly powerful analogy when read aloud in the theater, because they simultaneously demand that audience members confront the ways in which they're performing their own lives, remind them of their own mortality, and collapse the traditional boundary between actors on the stage and the audience watching them.

Analogy in Robert M. Pirsig's Zen and the Art of Motorcycle Maintenance

In Chapter 26 of Zen and the Art of Motorcycle Maintenance , the narrator attempts to describe his philosophical world view by drawing an analogy between knowledge and a train.

The narrator's concept of "Quality" refers to a holistic, balanced manner of existing in the world. The narrator believes that in modern life, we often fail to achieve Quality because we create an artificial distinction between an artistic, "Romantic" way of living life—being "in the moment," not stopping to analyze or reflect on things—and a scientific, "Classical" way of living life which involves analyzing how pragmatic things (like technology) work. Through the analogy of the Train, the narrator argues that both the Classical and Romantic modes of thought are necessary to living a balanced life in pursuit of Quality:

In my mind now is an image of a huge, long railroad train...In terms of the analogy, Classic Knowledge, the knowledge taught by the Church of Reason, is the engine and all the boxcars. All of them and everything that’s in them. If you subdivide the train into parts you will find no Romantic Knowledge anywhere. And unless you’re careful it’s easy to make the presumption that’s all the train there is. This isn’t because Romantic Knowledge is non-existent or even unimportant. It’s just that so far the definition of the train is static and purposeless...The real train of knowledge isn’t a static entity that can be stopped and subdivided. It’s always going somewhere. On a track called Quality...Romantic reality is the cutting edge of experience. It’s the leading edge of the train of knowledge that keeps the whole train on the track... The leading edge is where absolutely all the action is. The leading edge contains all the infinite possibilities of the future. It contains all the history of the past. Where else could they be contained?...At the leading edge there are no subjects. No objects, only the track of Quality ahead, and if you have no formal way of evaluating, no way of acknowledging this Quality, then the train has no way of knowing where to go.

Just as a train can't exist without its engine, its boxcars, or its lead locomotive, so too—the narrator argues—Quality cannot be pursued without applying both Classical and Romantic knowledge in a balanced way. This is a long and, obviously, complex example of analogy.

Analogy in Aravind Adiga's The White Tiger

The White Tiger tells the story of Balram Halwai, a self-made entrepreneur who (somewhat illegally) works his way up from the bottom rungs of the social ladder in Indian society. In Chapter 5, Balram introduces the analogy of the Rooster Coop to explain how members of the Indian elite repress the poor:

The greatest thing to come out of this country in the ten thousand years of its history is the Rooster Coop. Go to Old Delhi, behind the Jama Masjid, and look at the way they keep chickens there in the market. Hundreds of pale hens and brightly coloured roosters, stuffed tightly into wire-mesh cages, packed as tightly as worms in a belly, pecking each other and shitting on each other, jostling just for breathing space; the whole cage giving off a horrible stench – the stench of terrified, feathered flesh. On the wooden desk above this coop sits a grinning young butcher, showing off the flesh and organs of a recently chopped-up chicken, still oleaginous with a coating of dark blood. The roosters in the coop smell the blood from above. They see the organs of their brothers lying around them. They know they’re next. Yet they do not rebel. They do not try to get out of the coop. The very same thing is done with human beings in this country.

Balram uses the concrete, ordinary image of a rooster coop to explain the invisible but cruel forces constraining India's poor from making social progress. Not only does he use the rooster coop as an analog for his country, but he also uses it to justify his own behavior throughout the novel.

Why Do Writers Use Analogies?

Writers, and people in general, use analogies for a wide variety of reasons:

• To explain a new, unfamiliar concept in relatable and easy-to-understand terms.
• To help the reader make a new, insightful connection between two different entities.
• To appeal to the reader's sense of reason or logic when proving a point.

The anthropologist Mark Nichter once said (using an analogy) that "a good analogy is like a plow which can prepare a population's field of associations for the planting of a new idea." In other words, analogies pull together information and knowledge we have already stored to create novel combinations, which become the foundation for new ideas.

Other Helpful Analogy Resources

• The Wikipedia Page on Analogy: A very wide-ranging yet thorough explanation of analogy and its varied uses across disciplines.
• The Dictionary Definition of Analogy: A basic definition and etymology of the term—it comes from the Greek analogia meaning "proportion."
• Analogy in action: An interesting article from Entrepreneur Magazine entitled, "4 Leadership Lessons Learned From Orchestra Conductors."
• Analogy on Youtube: The "Ogres are like Onions" scene from Disney's Shrek .

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Analogy: Definition & Meaning (with Examples)

Analogy is one of the most common types of literary devices. It's also one of the hardest to understand because it's similar to other types of figurative language. Today, we're going to dive into the meaning of analogy with in-depth explanations and examples.

Analogy Definition: What Is an Analogy?

Let's start with the dictionary definition of an analogy. According to Merriam-Webster, an analogy is "a comparison of two otherwise unlike things based on a resemblance of a particular aspect."

We use analogies all the time in speaking and fields like history and science. They help us illustrate a point that might be hard to comprehend. For example, we might make an analogy between the Trail of Tears of U.S. History and the Jewish Diaspora of World History. In biology, you might discuss the analogous relationship of bat wings and bird wings.

As a literary device, however, analogy's meaning has more nuance that separates it from other types of rhetorical devices. Let's look at the literary meaning of analogy in more detail in the next section.

Analogy Meaning

As a rhetorical device, analogy compares two unlike things with the purpose of both illustrating a comparison and explaining it. You aren't just trying to show a similarity when you use an analogy. You are also trying to make a point about this similarity.

Analogies can be useful to explain complex concepts by comparing them to a familiar idea. Analogies also help paint a picture in a reader's mind and add emphasis to important ideas in writing.

Let's take a look at a popular example of an analogy from the movie Forrest Gump . In the movie, Forrest says that his mother always told him, "Life is like a box of chocolates—you never know what you're gonna get."

If Forrest just said that life was like a box of chocolates, we would wonder what the similarity is. What point is he trying to get across? It might be that life is sweet or that life is a gift from someone who loves you. But then he explains that we never know where life will take us or what circumstances we will fall into. We don't know until we get there; we can't see the future.

He's not just painting a picture about life. He's making a point about the uncertainty of life and the many twists and turns it takes. This analogy goes further and illustrates the entire premise of the film. Forrest goes from being a boy in leg braces to an international ping pong champion to a dad. No one could have predicted that!

Analogies look similar to other types of figurative language. So, what's the difference?

Analogy vs. Metaphor

A metaphor is a figure of speech that shows a likeness between two otherwise different things. The point of a metaphor is comparison. For example, we can say, "the kids were a bunch of monkeys today." We are comparing kids to monkeys.

An analogy not only compares but explains. "The kids were a bunch of monkeys today, climbing all over the furniture, running all over the house, and shrieking."

As you can see, an analogy might feature a metaphor, but it goes further in making a point. This is also different from an extended metaphor. An extended metaphor continues to use a comparison to illustrate similarities of two objects. An analogy requires some explicit explanation to make its point.

Analogy vs. Simile

A simile is a type of metaphor, but it uses "like" or "as" to draw comparisons. Just like with a metaphor, an analogy might use a simile to compare two things, but then the analogy goes on to explain the idea behind it.

The Forrest Gump quote is an example of this. The part of the quote, "Life is like a box of chocolates," is a simile. The next part of the quote that tells how life and a box of chocolates are related is what makes this quote an analogy.

Many analogies use similes and metaphors to make comparisons, but it is not required.

Analogy vs. Allusion

Another figurative language element that is easy to confuse with analogy is allusion.

Allusion is a mention of a person, place, or thing that is considered common knowledge. It's often a reference to a famous person or event or a well-known story, like fairy tales, myths, or religious parables.

Allusion is a way to compare two things. Let's look at an example:

• "The books on the top shelf were forbidden fruit."

Forbidden fruit refers to the fruit of the Tree of Knowledge in the Bible. This is an allusion. We can draw enough conclusions from this allusion to understand what the books represent.

Allusions can be part of analogies, too. Remember, where allusions compare, analogies explain:

• "If the library was Eden, the books on the top shelf were forbidden fruit. They opened my eyes to a world beyond the life I had always known."

All of these are useful types of figurative language. The difference lies in the purpose. If the goal is to explain an idea or get a specific point across, it's an analogy.

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Analogies, Idioms, and Clichés

Sometimes analogies become so well-known that they become part of our everyday lexicon. Idioms are phrases that don't make sense literally, but they do make sense figuratively. Overused idioms can become clichés.

An example of an analogy that is a cliché is "she's as blind as a bat." It's a very overused comparison. Use ProWritingAid's Clichés Report to help identify the clichés and idioms in your writing. While some common analogies might help you get your point across, some can actually hinder your writing's clarity, especially to non-native speakers.

Try the Cliché Report with a free ProWritingAid account.

Analogy Examples

You probably hear or read analogy examples all the time—they're a common rhetorical device. Today, we'll take a look at some analogy examples from everyday sentences and literature.

Examples of Analogy in a Sentence

Humans love figurative language, and we create analogies in our everyday speech. Here are some examples.

• Ordering clothes online is like playing the lottery. Some fit great, and some are a complete waste of money when they don't even go over your head!
• His voice was warm honey on toast, sweet and comforting and familiar.
• She thought the sound of babies crying was as annoying as fingernails on a chalkboard. Babies definitely weren't for her.

Can you create any analogies?

Examples of Analogy in Literature

Analogy is a powerful rhetorical device. Here are some famous examples of analogy in literature:

• "All the world’s a stage / And all the men and women merely players / They have their exits and their entrances / And one man in his time plays many parts / His acts being seven ages."— As You Like It , William Shakespeare
• “I can admire the perfect murderer—I can also admire a tiger—that splendid tawny-striped beast. But I will admire him from outside his cage. I will not go inside . . . . That is to say, not unless it is my duty to do so. For you see, Mr. Shaitana, the tiger might spring . . . .”— Cards on the Table , Agatha Christie
• "Memory is to love what the saucer is to the cup."— The House in Paris , Elizabeth Bowen

Tips on How to Write an Analogy

When you're writing an analogy to express an idea, it's important to keep two things in mind. First, make sure that at least one of the two things you're comparing is familiar and easy to understand. An analogy should make your point clear to the reader, not leave them confused! Animal or nature imagery, allusions to well-known tales, and everyday objects are good things to use in your analogies.

Secondly, make sure that your comparison is clear without much explanation. If you compare a shy, demure princess to a tiger, you need to explain what specific aspects of the princess and the tiger are similar. Is she ferocious when her loved ones are attacked? Does she prefer to spend time alone outdoors and seethe when caged?

If it takes too many sentences to explain the analogy, try using different imagery that is simpler to understand.

Different Types of Analogy

There are two main types of analogy. These are based on how closely related the two things being compared are.

Literal Analogy

The first type of analogy is a literal analogy. When two things are very closely related, we compare them with literal analogies. These are the types of analogies commonly used in science. Literal analogies can help scientists draw comparisons or make a logical argument.

For example, a virologist might compare the viral structure of two different viruses. If the virus has a similar structure and similar symptoms to another, they are analogous. This will help them theorize that the second virus can be treated similarly to the first.

Literal analogies don't have to be just for science! If you're a baker, you might know that you can make a cheesecake out of either cream cheese or mascarpone. As an analogy, we can say that mascarpone is a lot like cream cheese. They both have high fat content, are very soft, and are not aged.

Literal analogies are the type you might see on standardized tests. They used to feature on the SAT and looked like this: A:B::C:D. You can read literal analogies as "A is to B as C is to D."

Here's a simple example:

• Night is to sleep as morning is to wake .

Standardized tests would have one or more of the words blank, and you had to determine the connection in the analogy. How are they connected?

Figurative Analogy

A figurative analogy makes a comparison between two or more things that aren't necessarily that similar at first glance. The analogy focuses on making a comparison based on a specific aspect of the unrelated things. This is called shared abstraction .

Take a look at the following analogy:

• "Giving candy and coffee as appreciation gifts is just rearranging deck chairs on the Titanic. It's not actually fixing the issues that are causing low morale, like low pay, long hours, and micromanaging."

If the Titanic is sinking, it's pointless to rearrange deck chairs. Likewise, this quote suggests spending money on little gifts is pointless because it's not addressing the real issues at hand that are causing employee dissatisfaction.

No one is suggesting that low morale at a company is the same thing as the hundreds of lives lost on the Titanic. The shared abstraction is doing something pointless in the face of a disaster.

Should You Use Analogies in Your Writing?

Analogies are powerful literary devices because they create an image in the reader's mind while making a point in a deeper way than a metaphor. Remember, an analogy compares two objects with the purpose of explaining a deeper idea. A literal analogy compares two very similar objects, while a figurative analogy relies on shared abstractions.

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When & How to write an Analogy

• Definition & Examples
• When & How to write an Analogy

How to Write an Analogy

You should use analogies in your writing when you want to show strong support by comparison. Here are some examples of how to use them:

Normal Sentence:

He ran incredibly fast in the race.

With Analogy:

In the race, he ran with the grace and speed of a cheetah—smooth, flawless, and natural, as if he had been raised running across the plains of Africa.

Those two are very close.

Those two unlikely friends are surprisingly close, like a shark and its cleaner fish—though they have different qualities and purposes, it is clear that neither could survive without the

Although analogies are useful and essential devices, they can be surprisingly difficult to use effectively! You don’t want to make comparisons to just anything, or your writing may start to look sloppy and careless. Here are some examples of poor analogies to show you the kinds of common mistakes you should try to avoid:

Poor Analogy : He ran as fast as a cheetah in the race.

Why It’s Poor : Wait, there was a cheetah in the race? No, of course not. That phrase is a dangling modifier . So just move it to the beginning, as in the sentence above (“In the race, he ran…”).

Poor Analogy : On that warm summer day, we went down to the beach, where the sand was as white as snow.

Why It’s Poor : The author has done so much to show the reader that the setting is a warm, sunny beach in summer. But the word “snow” completely undermines that by bringing up images of cold, grey winter. Rather than improving  the imagery, the analogy actually works against it.

When to Use Analogy

Analogies can be an extremely powerful addition to your writing, so experiment! Using analogies is a really useful skill for improving your powers of logic, reasoning, and writing, and the best way to learn it is to practice.

When you experiment with analogies in your writing, keep the following principles in mind:

• Make sure it’s clear what aspect(s) of the two objects you want to compare.
• Draw an analogy to something concrete , ideally something that people can actually visualize in their minds. If you’re trying to explain an abstract idea, it doesn’t help to compare it to another abstract idea, but it might help a lot if you compare it to something tangible!
• If you’re using analogies in creative writing, make sure they’re suited to the setting ! If the story is set on a boat, try to use analogies having to do with water or islands. Remember the example with the sand and the snow. In that case, the problem was that the setting was all wrong – snow doesn’t belong on a warm, sandy beach!

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Analogy — Definition and Examples

What is an analogy?

An  analogy  is a comparison made to show how two things are similar for explanation or clarification. Although the things compared are physically different, the analogy identifies how they are figuratively similar.

Think of analogies as an extension of a metaphor or simile.

People use analogies to link unfamiliar ideas with common ones, making complex or abstract ideas easier to understand.

Analogy examples

It is common to use analogies to make comparisons in the English language. The following is an example analogy comparing a warrior's sword to a writer's pen:

Just as a sword is the weapon of a warrior, a pen is the weapon of a writer.

A warrior uses his sword as a weapon, while a writer's weapon is their words written with their pen.

In the next example, the analogy is comparing a book to a rollercoaster:

That book was a rollercoaster of emotion.

The book's plot had many emotional highs and lows, making it feel like you rode the ups and downs of a rollercoaster.

Analogy examples in literature

Analogies are commonly used in literature. A famous example can be found in  Romeo and Juliet  by William Shakespeare:

What’s in a name? That which we call a rose, / by any other word would smell as sweet. / So Romeo would, were he not Romeo called.”

This analogy is saying a rose would smell the same even if it were called something different; therefore, Romeo's name does not define him.

Another example from literature is found in George Orwell's  Animal Farm:

The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.

In Orwell's analogy, the pigs have become that which they fought against (man).

The House in Paris  by Elizabeth Bowen contains this analogy:

Memory is to love what the sauce’r is to cup.

Like a saucer holds a cup, a memory holds onto love.

Analogy in poetry

Types of analogies.

An analogy can be both a literary device and a rhetorical device, depending upon its use.

As a rhetorical device, word analogies are often found on standardized tests. This assesses the test taker's ability to identify various relationships.

When writing a word analogy as a rhetorical device, colons stand in for words. Analogies written in this way use pairs of words to make a logical argument. Consider the following example:

Stove is to kitchen as bed is to bedroom

Stove : kitchen :: bed : bedroom

There are a variety of types of rhetorical verbal analogies that identify different kinds of relationships:

Analogy vs. metaphor vs. simile

A metaphor is a figure of speech used to compare or suggest a similarity between two items, whereas a simile is a comparison that uses the words "like" or "as." While metaphors and similes help writers show instead of tell, an analogy provides explanation or clarification.

Consider the following example comparing thoughts to a storm:

Metaphor : His thoughts were a storm.

Simile : His thoughts were like a storm.

Analogy : His thoughts were like a storm causing chaos.

Writers can use metaphors and similes to create analogies; however, not all metaphors and similes are analogies.

Learn more about  difference between metaphors, similes, and analogies .

Analogical arguments

Analogical reasoning is any thinking that involves an analogy. It compares something new with something known. Argument by analogy is a way to inform, persuade, or explain, such as in the following examples:

The new movie is supposed to be similar to the one that came out last summer, so it too is probably dull.

Not everyone had a computer in their homes 20 years ago, but most of them do now; therefore, one can expect the same of virtual reality.

The new planet is the same distance from its star as the Earth is from the sun, meaning it could support life.

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What Is an Analogy? Analogy Meaning and 100+ Analogy Examples

You may be wondering what an analogy is. While the concept is long gone from the SAT test, analogies are still used a great deal in everyday life. We’ll explore what an analogy is and give you some analogy examples in this article.

Table of Contents

What Is an Analogy?

An analogy is a comparison of two things in which one idea or concept is compared to something entirely different. While the two things might be totally different, the analogy compels the readers to realize their association. Sometimes, the analogy provides a comparison between two similar things, one of which might be hidden. The analogy gives a reader a way to understand the hidden thing by picturing the more common thing.

According to Merriam-Webster , an analogy is a comparison of two unlike things based on the resemblance of a particular aspect.  See the following example:

Life is like a box of chocolates – you never know what you are going to get. – Forrest Gump

In this case, Forrest Gump is comparing life to a box of chocolates.This exact comparison is considered a simile as we’ll get to in the next section.

In this post, we will learn about different types of analogy and their examples. So, without delay let’s get started.

Where Does the Word “Analogy” Come From?

The word analogy comes from the Greek word analogia. The word is made of the prefix ana and suffix logos . Ana means “again,” “upon,” or “back,” while the word logia means “ speech,” “word,” or “ratio. ” Together the word means something similar to “proportion.”

What Are the Different Types of Analogy?

The following literary devices qualify as analogies. Let’s learn about them one-by-one.

A metaphor is a figure of speech that makes an implied or hidden comparison between two things that are not related, but share common characteristics . For example, “He is the black sheep of the family, ”

Here the black sheep phrase is used to indicate a person who is considered worthless by other people in that family. However, it does not mean the person is actually black or sheep.

A metaphor compares two subjects without using words such as “as,” “like,” etc. Since metaphors declare one thing is another, they are regarded as an intense form of an analogy.

Like a metaphor, this analogy also creates a comparison between two things. However, it uses connecting words such as “as” or “like.” While it’s not as strong as a metaphor, it still lets the reader understand the similarity between two things and make a new cognitive link.

Your voice is as sweet as sugar.

A parable is generally a fictitious short story that illustrates an educational lesson or principle. Some of the popular fables that are parables include:

• The Fox and The Crow – Aesop
• The Lion and the Mouse – Aesop
• The Tortoise and the Hare – Aesop

Like a parable, allegory is also a story in which characters act as symbols. These symbols can be interpreted to explain a moral truth or a historical situation.

Animal Farm by George Orwell is a perfect example of Allegory.

Exemplification

Exemplification uses various examples to add more information to a general idea. It is a relationship between a sample and what that sample refers to.

Example from Wikipedia : “For instance, when a patch of green paint is used as a colour sample. The sample refers to green by possessing it and thus being referred to by the word denoting it. The sample  exemplifies  green, it stands for it, and in this way  exemplification is a mode of reference.”

Analogy Examples in Everyday Use

• Time is money, so spend it wisely.
• His brother is sly like a fox.
• She is as busy as a bee nowadays.
• She is as light as a feather.
• Socks are just the gloves of the feet.
• She found it under a blanket of sand.
• There is a garden on his face.
• The new parents have stars in their eyes.
• He is living in a bubble.
• Finding the right person is like finding a needle in a haystack.
• My father is my rock in hard times.
• Talking to her is like talking to a brick wall.
• Last night I slept the sleep of the dead.
• I would be pleased to meet your better half.
• My brother is as strong as an ox.
• He was as quiet as a church mouse.
• Always see the problem as a speed bump, not a roadblock.
• He was quick like a bunny.

Analogy Examples in Literature

The analogy has a significant role in literature. Authors use it to make a comparison between similar or dissimilar things, to help readers imagine places and characters, and to suggest a more profound significance . Greek philosophers such as Aristotle and Plato also fostered analogy in literature, calling it a shared abstraction. Check out some classic examples of analogies in literature.

Romeo and Juliet by William Shakespeare

“What’s in a name? That which we call a rose by any other word would smell as sweet. So Romeo would were he not Romeo called.”

In the above lines of the play, you can notice Shakespeare used the analogy to equate Romeo to a rose’s sweetness.

The House in Paris by Elizabeth Bowen

“Memory is to love what the saucer is to the cup.”

Bowen’s novel The House in Paris also uses analogy smartly in various places. For example, in the above phrase, the writer used the analogy to compare a cup and saucer’s relationship with love and memory.

Macbeth by William Shakespeare

“Life’s but a walking shadow, a poor player that struts and frets his hour upon the stage.” 

In Act 5 of his tragic play Macbeth, William Shakespeare used the analogy to compare life to a passing shadow.

Let Me Count the Ways by Peter De Vries

“If you want my final opinion on the mystery of life and all that, I can give it to you in a nutshell. The universe is like a safe to which there is a combination.”

In the above example of analogy, Vries compares the universe to a safe which can’t be unlocked.

Analogy Examples

Analogies play an essential role in writing to explain something important by comparing two different things that have some common traits. However, in verbal and word analogies, they are more like logic puzzles. The word or verbal analogies also compare two different things, but they do so by breaking them into parts to notice how they are related .

See the following examples of word analogies.

Moon :night :: sun :day

When you read the above analogy aloud, it says the moon is to night as the sun is to day.

Let’s have a look at some more word analogies.

• Pencil :write :: scissors :cut
• Apple :fruit :: carrot :vegetable
• Football: field :: tennis :court
• Hot :oven :: cold refrigerator
• Cow :mammal :: snake :reptile
• Turtle :crawl ::frog :hop
• Bow :arrow ::bat :ball
• Raft :river ::ski :snow
• Pretty :ugly :: smile: frown
• Bedroom :sleeping :: Kitchen :cooking
• Football :field :: tennis :court.

Analogies used to be a section in the SAT exam , but they were removed in 2005 since these questions were criticized for being irrelevant to success in a college or work environment.

So these are some analogy examples. We hope they improve your understanding of an analogy.

What is a false analogy?

An analogy compares two premises for what they both have in common. A false analogy implies a link between two premises based on what those two premises have in common. In other words, if two objects have one attribute in common, then they must have other attributes in common.

An easy false analogy example is:

Bob and Mark both drive sedans. Bob is a doctor so therefore Mark must also be a doctor.

Analogies and false analogies can both be used in an argument, but where the analogy would be derived from a fact, a false analogy would be based on a hypothesis. Whereas an analogy would be used as a rhetorical device in favor of a winning argument, a false analogy would be a misleading deduction based on the speaker’s lack of insight.

Classic Analogies

Classic analogies are known for their powerful imagery and ingenuity. False analogies are often dismissed for their obvious lack of logic and imagination. Classic analogies are often found in literature.

In his play, “Romeo and Juliet”, Shakespeare would of often use analogies to have his characters put into words the feelings they would otherwise not know how to express. In the famous balcony scene in “Romeo and Juliet”, Juliet is caught trying to persuade herself not to hide her feelings from her lover, as Romeo hears her saying

“What’s in a name? That which we call a rose by any other word would smell as sweet”.

Juliet is thus establishing a comparison between her lover’s name and that of a rose’s. She does so through an analogy: she compares her lover’s name to that of a rose’s , so she can find them both beautiful, yet completely devoid of meaning.

Had she used a false analogy, she would have had to compare her lover’s features to that of a rose’s, in order to win the argument. She would have had to compare Romeo’s hair to a rose’s petals and his feet to a rose’s stalk and her entire argument would have collapsed.

Just because Romeo’s name sounds as sweet as that of a rose’s, that doesn’t mean that Romeo would need to shares any of his other qualities with a rose. Had she built from a premise of them sharing the same beautiful sounding name, she would have reached a false conclusion, as that sweet loving sound is the only link between them.

The fact that her Romeo and a rose could be called by any other name is the only comparison she needs. The reason she picked a rose is that she needed a subject completely unrelated to her Romeo. She needed an analogy to get her point across. She got one.

100 Examples of Word Analogy

Below are 100 examples of anlaogies.

1. Rose is to flower as blue is to color 2. Father is to mother as uncle is to aunt 3. Puppy is to dog as kitten is to cat 4. In is to out as up is to down 5. Hearing is to ear as seeing is to eye 6. State is to country as country is to continent 7. Rock is to mountain as sand is to beach 8. Cover is to book as pillowcase is to pillow 9. Captain is to ship as pilot is to airplane

10. Snowflake is to snow as raindrop is to rain 11. Mother is to child as cub is to bear 12. Hat is to head as gloves are to hands 13. Penny is to dime as $1 bill is to $10 bill 14. Key is to a lock as combination is to a safe 15. Big is to little as wide is to narrow 16. Canoe is to ship as car is to bus 17. White is to black as day is to night 18. Chair is to sit as bed is to lay down 19. United States is to Washington DC as Albany is to New York

20. Meow is to cat as bark is to dog 21. Beach hat is to summer as earmuffs are to winter 22. Cheering fans are like squawking turkeys 23. Waiting for a special day is like watching grass grow 24. Homeruns are to baseball as touchdowns are to football 25. Colorful leaves are to autumn as buds are to spring 26. Vacation is to fun as workdays are to drudgery 27. Ants are to beetles as sparrows are to crows 28. Recycling is to ecology as dumping is to pollution 29. A full moon is like a glow-in-the-dark frisbee

30. A furnace is to heat as an air-conditioner is to cool 31. A compliment is to an insult as a smile is to a scowl 32. Babe Ruth is to baseball as Michael Jordan is to basketball 33. Flying a kite without wind is like sledding without snow 34. Assembling furniture with no instructions is like driving in the dark with no headlights 35. Uninvited guests are like ants at a picnic 36. Reading a good novel is like going on an adventure 37. Words are to sentences as numbers are to equations 38. A solution to a problem is like a cure to an illness 39. Math is to numbers as English is to letters

40. Paper is to origami as clay is to sculpture 41. Coach is to a team as a conductor is to an orchestra 42. A bullseye is to archery as a hole in one is to golf 43. Dermatologist is to doctor as orthodontist is to dentist 44. Arborist is to tree as veterinarian is to animal 45. Keys are to piano as strings are to guitar 46. Commercials are to television as ads are to magazines 47. Trophy is to achievement as souvenir is to vacation 48. Breakfast is to morning as dinner is to evening 49. Heroes are courageous as cowards are afraid

50. Verses are to greeting cards as lyrics are to songs 51. Robin is to bird as poodle is to dog 52. Run is to jog as walk is to amble 53. Panes are to windows as shingles are to roofs 54. Eraser is to pencil as stain remover is to carpet 55. Gift wrap is to gift as mailing envelope is to package 56. Bland is to spicy as white bread is to jalapeno 57. Pumpkin is to orange as pine tree is to green 58. Tree is to forest as person is to crowd 59. Pitcher is to baseball as quarterback is to football

60. Black cat is to Halloween as reindeer is to Christmas 61. Broccoli is to vegetable as apple is to fruit 62. Monopoly is to board games as Old Maid is to card games 63. Garages are to cars as stables are to horses 64. Pediatricians are to children as veterinarians are to pets 65. Drumsticks are to drummers as paintbrushes are to painters 66. Icing on a cake is like sprinkles on ice cream 67. A kangaroo’s pouch is like a mother’s baby carrier 68. Lose is to find as fail is to succeed 69. Sickness is to health as poverty is to riches

70. Education is to teacher as healthcare is to doctor 71. Tan is to brown as pink is to red 72. Old-fashioned is to modern as Model T Ford is to Tesla 73. Quaint is to village as fast-paced is to city 74. Goalie is to hockey team as catcher is to baseball team 75. Seamstress is to fabric as carpenter is to wood 76. A nail is to a hammer as a screw is to a screwdriver 77. Trout is to fish as finch is to bird 78. Knee is to leg as elbow is to arm 79. Polite is to rude as generous is to stingy

80. Driver is to car as pilot is to airplane 81. East is to west as north is to south 82. Trial is to courtroom as wedding is to banquet hall 83. Flower is to bouquet as a charm is to a charm bracelet 84. Fish is to fin as bird is to wing 85. Crossword is to puzzle as mystery is to novel 86. Mason is to brick as painter is to paint 87. Grazing is to sheep as snacking is to people 88. Wound is to painful as hive is to itchy 89. The Nutcracker is to ballet as Carmen is to opera

90. Earrings are to ears as bracelets are to wrists 91. Article is to newspaper as show is to television 92. Skiing is to winter as surfing is to summer 93. Lanes are to bowling as courts are to tennis 94. Ovens are for baking as toasters are for toasting 95. Bear is to mammal as crocodile is to reptile 96. Spain is to Europe as Venezuela is to South America 97. Clock is to time as thermometer is to temperature 98. Worm is to soil as sandworm is to sand 99. California is to west coast as Florida is to east coast 100 Trowel is to gardening as a glue gun is to crafting

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30 Writing Topics: Analogy

Ideas for a Paragraph, Essay, or Speech Developed With Analogies

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• An Introduction to Punctuation
• Ph.D., Rhetoric and English, University of Georgia
• M.A., Modern English and American Literature, University of Leicester
• B.A., English, State University of New York

An analogy is a kind of comparison that explains the unknown in terms of the known, the unfamiliar in terms of the familiar.

A good analogy can help your readers understand a complicated subject or view a common experience in a new way. Analogies can be used with other methods of development to explain a process , define a concept, narrate an event, or describe a person or place.

Analogy isn't a single form of writing. Rather, it's a tool for thinking about a subject, as these brief examples demonstrate:

• "Do you ever feel that getting up in the morning is like pulling yourself out of quicksand? . . ." (Jean Betschart, In Control , 2001)
• "Sailing a ship through a storm is . . . a good analogy for the conditions inside an organization during turbulent times, since not only will there be the external turbulence to deal with, but internal turbulence as well . . ." (Peter Lorange, Leading in Turbulent Times , 2010)
• "For some people, reading a good book is like a Calgon bubble bath — it takes you away. . . ." (Kris Carr, Crazy Sexy Cancer Survivor , 2008)
• "Ants are so much like human beings as to be an embarrassment. They farm fungi, raise aphids as livestock, launch armies into wars, use chemical sprays to alarm and confuse enemies, capture slaves. . . ." (Lewis Thomas, "On Societies as Organisms," 1971)
• "To me, patching up a heart that'd had an attack was like changing out bald tires. They were worn and tired, just like an attack made the heart, but you couldn't just switch out one heart for another. . . ." (C. E. Murphy, Coyote Dreams , 2007)
• "Falling in love is like waking up with a cold — or more fittingly, like waking up with a fever. . . ." (William B. Irvine, On Desire , 2006)

British author Dorothy Sayers observed that analogous thinking is a key aspect of the writing process . A composition professor explains:

Analogy illustrates easily and to almost everyone how an "event" can become an "experience" through the adoption of what Miss [Dorothy] Sayers called an "as if" attitude. That is, by arbitrarily looking at an event in several different ways, "as if" if it were this sort of thing, a student can actually experience transformation from the inside. . . . The analogy functions both as a focus and a catalyst for "conversion" of event into experience. It also provides, in some instances not merely the To discover original analogies that can be explored in a paragraph , essay, or speech, apply the "as if" attitude to any one of the 30 topics listed below. In each case, ask yourself, "What is it like ?"

Thirty Topic Suggestions: Analogy

• Working at a fast-food restaurant
• Moving to a new neighborhood
• Starting a new job
• Quitting a job
• Watching an exciting movie
• Reading a good book
• Going into debt
• Getting out of debt
• Losing a close friend
• Leaving home for the first time
• Taking a difficult exam
• Making a speech
• Learning a new skill
• Gaining a new friend
• Responding to bad news
• Responding to good news
• Attending a new place of worship
• Dealing with success
• Dealing with failure
• Being in a car accident
• Falling in love
• Getting married
• Falling out of love
• Experiencing grief
• Experiencing joy
• Overcoming an addiction to drugs
• Watching a friend destroy himself (or herself)
• Getting up in the morning
• Resisting peer pressure
• Discovering a major in college
• 501 Topic Suggestions for Writing Essays and Speeches
• The Value of Analogies in Writing and Speech
• Classification Paragraph, Essay, Speech, or Character Study: 50 Topics
• Understanding Analogy
• 30 Writing Topics: Persuasion
• Learn How to Use Extended Definitions in Essays and Speeches
• Development in Composition: Building an Essay
• 60 Writing Topics for Extended Definitions
• Topic In Composition and Speech
• Definition and Examples of Transitional Paragraphs
• List of Topics for How-to Essays
• How to Structure an Essay
• How to Write a Narrative Essay or Speech
• The Ultimate Guide to the 5-Paragraph Essay
• Using Word Analogies
• Conclusion in Compositions

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Part Six: Evaluating Inductive Logic

Chapter Fifteen: Arguments from Analogy

Arguments that make their point by means of similarities are impostors, and, unless you are on your guard against them, will quite readily deceive you. —Plato

Analogies decide nothing, that is true, but they can make one feel more at home. —Sigmund Freud, New Introductory Lectures on Psychoanalysis

Correct Form for Arguments from Analogy

• The Total Evidence Condition (1): Relevant Similarities
• The Total Evidence Condition (2): Irrelevant Dissimilarities
• The Special Character of Arguments from Analogy

Arguments from analogy declare that because two items are the same in one respect they are the same in another. As Freud notes, they can make you feel at home—and for that reason they can be especially persuasive.

During World War I, the Socialist Party distributed leaflets to recent draftees, urging them to oppose the draft. The draft, they contended, violated the constitutional amendment against involuntary servitude. Oliver Wendell Holmes, chief justice of the Supreme Court, argued that they did not have the right to circulate the leaflets during wartime. The right to free speech, he asserted, “would not protect a man in falsely shouting fire in a theater and causing a panic.” Since in both cases “the words used . . . create a clear and present danger,” he concluded, the right to free speech did not protect the Socialists in expressing ideas that might harm the war effort. The argument begins with something familiar—of course we don’t have the right to falsely shout fire in a theater—and invites us to conclude the same about something less familiar—under certain circumstances we don’t even have the right to explain to others our interpretation of the U.S. Constitution. (Holmes is often quoted as calling it “a crowded theater.” He didn’t, though it is probably what he had in mind.)

Arguments from analogy are almost always enticing because, by their very nature, they use two of the quick-and-dirty shortcuts in reasoning described in Chapter 1. By beginning with the familiar, they exploit our dependence on the vividness shortcut; and by presenting similarities between the familiar and the unfamiliar, they take advantage of our dependence on the similarity shortcut. They are custom-made for the way our minds naturally operate. This makes us especially susceptible to them and heightens the importance of being able to evaluate them effectively.

15.1 Correct Form for Arguments from Analogy

Analogies are often used merely for rhetorical effect. Acel Moore of the Philadelphia Inquirer, for example, writes: “Writing editorials is a lot like wearing a navy blue suit and standing in a rainstorm on a cold day and wetting your pants; it may give you a warm feeling for a minute, but no one else is going to notice.” Moore doesn’t attempt to establish any conclusion based on the similarity—he simply makes note of it. Don’t jump to the conclusion that an analogy introduces an argument unless there really is—at least implicitly—a conclusion.

When there is an argument from analogy , as in the preceding free speech argument, it can typically be clarified according to the following form:

• A is F and G.

A and B, as always, are used here as name letters. They name the two analogs [1] —that is, the two things (or classes of things) that are said to be analogous. A, the basic analog , is the one that we are presumed to be more familiar with; in the free speech argument it is falsely shouting fire in a theater. B, the inferred analog , is the thing in question, the one that the argument draws a conclusion about; in the free speech argument it is expressing ideas that might harm the war effort.

We will continue to use F and G as property letters. F is the basic similarity , the property that the two analogs share, presumably without controversy. In the free speech argument, the basic similarity is that they create a clear and present danger. And G is the inferred similarity , the property that the inferred analog is purported to have on the grounds that the basic analog has it. Is not protected by the right to free speech is the inferred similarity in the free speech argument. Here is one good way to clarify the argument:

• Falsely shouting fire in a theater creates a clear and present danger and is not protected by the right to free speech.
• Expressing ideas that might harm the war effort creates a clear and present danger.
• ∴ Expressing ideas that might harm the war effort is not protected by the right to free speech..

Variations on this model are common. The basic or inferred analog, for example, will sometimes include more than one item, as in this example:

Manatees must be mammals, since whales and dolphins, like manatees, are sea creatures that give live birth, and whales and dolphins are definitely mammals.

In this case, the basic analog—the content of A —is whales and dolphins.

Likewise, either the basic similarity or the inferred similarity may include more than one property, as in this example:

Manatees must be mammals, since whales, like manatees, are sea creatures that give live birth and that nourish their young on the mother’s milk, and whales are definitely mammals.

In this example, the basic similarity—the content of F —is sea creatures that give live birth and nourish their young on the mother’s milk.

Clarifying an argument from analogy is usually a straightforward matter. It is easiest to begin by identifying the analogs—the two items that the arguer is comparing; insert the one that is not in question into the A position as the basic analog, and the one that is in question into the B position, as the inferred analog. Then insert the basic similarity—the property the two analogs uncontroversially share—into both premises as F. Finally, insert the inferred similarity into the first premise and the conclusion, as G.

Arguments from analogy are sometimes enthymemes. When there is an implicit statement, it is usually the second premise, the one that establishes the basic similarity. This is because arguers often assume, rightly, that the similarity between two analogs is so obvious that it goes without saying. Suppose I say to a friend of mine, whose son is about to enter first grade, “Since John behaves respectfully towards his parents, he will surely treat his teachers with respect.” The basic analog is John’s parents, the inferred analog is John’s teachers, and the inferred similarity is are treated with respect by John. But what is the basic similarity? We must identify a relevant trait that parents and teachers have in common, namely, that they are authority figures to John. Here is the clarified argument. (Brackets, as usual, indicate that premise 2 is implicit, but we also must supply to premise 1 the part about authority figures.)

• John’s parents are authority figures to him and are treated with respect by him.
• [John’s teachers will be authority figures to him.]
• ∴ John’s teachers will be treated with respect by him.

EXERCISES Chapter 15, set (a)

For each of these arguments from analogy, identify the basic analog, the inferred analog, the basic similarity, and the inferred similarity. Then clarify it in standard clarifying format.

Sample exercise. “Expressions of shock and sadness came from other coaches and administrators following the announcement by Tulane President Eamon Kelly that the school planned to drop its basketball program in the wake of the alleged gambling scheme and newly discovered NCAA violations. Coach Jim Killingsworth of TCU said: ‘I think they should deal with the problem, not do away with it. If they had something like that happen in the English department, would they do away with that? I feel like they should have tried to solve their problems.’” —Associated Press

Sample answer. Basic analog: English department. Inferred analog: basketball program. Basic similarity: is a college program (implicit). Inferred similarity: should not be eliminated if experiencing problems.

• The English department is a college program and should not be eliminated if it is experiencing problems.
• [The basketball program is a college program.]
• ∴ The basketball program should not be eliminated if it is experiencing problems.
• In a good marriage, partners often seek counseling to help them resolve their difficulties. You’re having trouble with your boss—why should a conflict in an employer–employee relationship be treated any differently?
• So you got tickets to the Metropolitan Opera’s production of the “Flying Dutchman”? You should try to smuggle in a flashlight and a good book. I made the mistake of going to Wagner’s “Parsifal”—that night was one of the most boring years of my life.
• Etiquette arbiter Emily Post contended that men need not remove their hats in elevators when there are women present. She reasoned that an elevator is a means of transportation, just like a streetcar, bus, subway, or train. The only difference is that an elevator travels vertically, rather than horizontally. A man is not expected to remove his hat in other vehicles, so there is no need for him to do so in an elevator.
• View expressed in a mid-20th century article by a professional sociologist: One attribute with which women are naturally and uniquely gifted is the care of children. Since the ill and infirm resemble children in many ways, being not merely physically weak and helpless but also psychologically dependent, it is fairly easy to conclude that women are also especially qualified to care for the sick.
• “Suppose you had a son, a fine writer who had brought national recognition for his college newspaper and a scholarship for himself. Suppose that, in his junior year, a big-city newspaper offered him a reporter’s job with a three-year guarantee at an unheard-of salary. Would you advise him to turn down the offer of a professional newspaper job? We know the answer. And we would not think twice before urging him, begging him, to hire on with the newspaper. After all, we’d say, the reason he was in college was to start to prepare himself for a decent career in the field of his choosing. So, why all the fulmination about a star athlete’s taking the chance to make himself a cool $5 million by doing for pay what he’s been doing for free (presumably) for three years?” —William Raspberry, Los Angeles Times
• “We feel instinctive sympathy for the defendant who pleads, ‘I tried to get a job and nobody would hire me. Only in desperation did I turn to robbery.’ Now consider the logically parallel defense: ‘I tried to seduce a woman legitimately and nobody would sleep with me. Only in desperation did I turn to rape.’ Nobody would buy that from a rapist, and nobody should buy it from a robber.” —Steven Landsburg, Forbes

15.2 The Total Evidence Condition (1): Relevant Similarities

If an argument from analogy can be loyally paraphrased in the form described above, then it satisfies the correct form condition. But for an inductive argument to be logically strong it must not only satisfy the correct form condition; it must also satisfy the total evidence condition. As with frequency arguments and inductive generalizations, there are two parts to the total evidence condition for arguments from analogy: the basic similarity must be relevant, and any dissimilarities must be irrelevant. If an argument does poorly on either one of these conditions, it should be judged no better than logically weak.

Although analogical arguments are sometimes accused of committing the fallacy of false analogy (or the fallacy of faulty analogy ), this fallacy is very much like the fallacy of hasty generalization. The existence of the named fallacy highlights the ease with which we can make mistakes in this sort of reasoning. But to accuse an argument from analogy of committing this fallacy says nothing about what has gone wrong with the argument. It is far better to explain more specifically how it is that some necessary condition for soundness has not been satisfied.

Total Evidence Condition for Arguments from Analogy

• The basic similarity must be relevant —it must count in favor of the inferred similarity.
• The dissimilarities must be irrelevant —any dissimilarity between the two analogs must not make the basic analog a better candidate for the inferred property.

The argument is logically weaker to the extent that it fails in either area.

15.2.1 The Relevance of the Basic Similarity

Begin your deliberations about the total evidence question by asking, Is the basic similarity relevant? The more relevant it is, the stronger the logic of the argument might be. When you consider this question, forget about the two analogs and simply consider to what extent the basic similarity counts in favor of the inferred similarity. A television advertising campaign by a dairy company shows old but cheerful citizens of the Republic of Georgia eating yogurt; they have eaten yogurt all their lives, we are told, and they are now well past the century mark—one woman is now 134! Eating yogurt, we are encouraged to believe, could do the same for us. The first step in evaluating how well this argument satisfies the total evidence condition is to ignore the two analogs (citizens of Georgia and us) and ask whether the basic similarity—eating yogurt—counts in favor of the inferred similarity—a long life. There is no special reason to think so, and the argument doesn’t help by providing one. So the logic of the argument is very weak.

More commonly an argument from analogy satisfies the condition at least to some degree. One large state university published the following story in its alumni magazine:

A preliminary appraisal of the results of a major assessment of faculty and graduate programs conducted by the Conference Board of Associated Research Councils placed our institution second in the nation among public research universities and in the top five overall. “It is gratifying to see our faculty receive this national recognition of their superior research and teaching,” said the Chancellor. Even though the study focused on graduate programs, he pointed out that the results could also be applied to the undergraduate program as well, since the two programs share the same faculty.

The university’s graduate program is the basic analog and its undergraduate program the inferred analog. The basic similarity is that the university’s excellent faculty staffs them. And the inferred similarity is that the academic programs are excellent. Is the basic similarity relevant? That is, does having an excellent faculty count toward the excellent academic programs? Of course it does. So this argument easily clears the first hurdle of the total evidence condition. But it is too soon to conclude that the argument is logically strong; there is still a second total evidence hurdle to clear.

15.2.2 Relevant Similarities and the Fallacy of Equivocation

Suppose I say, “Einstein was smart, and he was able to revolutionize physics. The physics teacher I had in high school is smart, too, so he should be able to revolutionize physics.” The basic similarity is relevant to the inferred similarity—smart is better than stupid when it comes to revolutionizing physics. But there is smart, and then there is smart. Surely my high school physics teacher is not as smart as Einstein. Doesn’t that weaken the argument? Let’s clarify it and see:

• Einstein was smart and was able to revolutionize physics.
• My high school physics teacher is smart.
• ∴ My high school physics teacher is able to revolutionize physics.

Smart shows up in both premises. To ask whether my high school physics teacher is as smart as Einstein is to ask, in effect, whether the word means the same thing in each case. It is a general expression. Recalling our coverage of generality in Chapter 5, this means that it is an expression that allows for degrees (examples were fine, bald, brown, living together, incompatible, wrong, and evil ). As we saw, generality is usually unproblematic. It becomes problematic, however, when the meaning of the expression shifts from one use to the next, and when the apparent success of the argument depends on that shift. In that case, the argument commits the fallacy of equivocation; the lesson from Chapter 5 is to eliminate the ambiguity.

Let’s eliminate the ambiguity by using the reasonable-premises approach in revising premise 2; in that case it is as follows:

2. My high school physics teacher is smart, though not as smart as Einstein.

While this is probably true, we now have a major problem with the logic of the argument—namely, it no longer satisfies the correct form condition, since the basic similarity, established in premise 1, is not asserted in premise 2. (The form is now something like this: 1. A is F and G; 2. B is sort of like F ; ∴ C . B is G. ) Let’s try revising it again, this time using the reasonable-logic approach. This gives us the following:

2. My high school physics teacher is just as smart as Einstein.

This nicely fixes the logical problem, but at the cost of what is pretty obviously a false premise. Either way, the argument is unsound.

The Oliver Wendell Holmes free speech argument, presented at the beginning of the chapter, provides a weightier example of the same problem. The basic similarity, creating a clear and present danger, certainly counts in favor of the inferred similarity of not being protected by the right to free speech. But is the danger caused by the wartime expression of potentially subversive ideas as clear and as present as the danger caused by the false shout of fire in a theater? If not, doesn’t this weaken the argument? Let’s take another look at Holmes’s clarified argument.

• ∴ Expressing ideas that might harm the war effort is not protected by the right to free speech.

The phrase clear and present danger, like the term smart in the Einstein example, is a general term that seems to apply to a greater degree in premise 1 than in premise 2. It is plausible to suppose that this shift contributes to the apparent success of the argument, and thus that the argument commits the fallacy of equivocation. So we should revise our paraphrase of premise 2 to eliminate the ambiguity. On the one hand, we could paraphrase it to say that those who scattered the leaflets created a clear and present danger, though less clear and present than falsely shouting fire in a theater. The premise would probably be true, but we would have created the same logical difficulty described in the Einstein argument—the basic similarity is not the same in each premise. On the other hand, we could paraphrase it to say that they created a clear and present danger that is just as clear and present as falsely shouting fire in a theater. We have now satisfied the correct form condition but probably have a false premise.

The problem is one to look for whenever you are clarifying an argument from analogy.

EXERCISES Chapter 15, set (b)

For each of the arguments in set (a), answer whether the basic similarity is relevant.

Sample exercise. See sample in set (a).

Sample answer. The basic similarity (that something is a college program) has some relevance to the inferred similarity (that it shouldn’t be eliminated if it is experiencing problems), but only to a limited extent. It is relevant only insofar as there is some weak presumption in any sort of institution that a program that has been set up was set up for a good reason.

15.3 The Total Evidence Condition (2): Irrelevant Dissimilarities

15.3.1 the irrelevance of the dissimilarities.

The second total evidence question is Are there relevant dissimilarities? Preferably they are irrelevant, for the more relevant the dissimilarities, the weaker the logic of the argument. When you consider this question, forget about the basic similarity and concentrate on the two analogs. There are always innumerable ways in which they are dissimilar, but most or all of them will be irrelevant. What matters is to what extent any dissimilarity makes the basic analog a better candidate for the inferred property.

Consider, for example, the free speech argument. There are many dissimilarities. One of the activities happens in a theater, for example, while the other could happen anywhere; but this is irrelevant, since there is no reason to think that things said in a theater are less deserving of protection by the right to free speech than things said anywhere else. Or, for example, one of them is spoken aloud, while the other could be written down; but again, this is irrelevant, for there is no general reason to think that the spoken word is more worthy of free speech protection than the written word.

Some of the dissimilarities, however, are relevant. In the theater case, what is expressed is intentionally deceptive, while in the leaflet case, what is expressed seems to have been utterly sincere. This, taken by itself, certainly makes the theater case a better candidate for exemption from free speech protection, and thus it counts as a relevant dissimilarity. Furthermore, in the theater case, the action is sure to have a harmful result; but in the leaflet case, there is no assurance that anyone will pay any attention or, if they do, that they will be influenced (in fact, it was established that no one had been persuaded by the leaflet). This, too, makes the theater case a better candidate for lack of protection by the right to free speech.

In short, even if we forget that the phrase clear and present danger may be equivocal, the argument does not score well on the second portion of the total evidence condition. Its logic can be judged, at best, as fairly weak. Brilliant jurist that he was, I should note that Oliver Wendell Holmes relied, as he should have, on a good deal more than just this argument in support of his conclusion.

Let’s now return to the academic excellence argument. Here is the clarification:

• The university’s graduate program is staffed by the university’s faculty and is academically excellent.
• The university’s undergraduate program is staffed by the university’s faculty.
• ∴ The university’s undergraduate program is academically excellent.

There are many dissimilarities between the graduate and undergraduate programs of any large state university. Graduate courses, for example, are usually assigned higher catalog numbers than are undergraduate courses. But this is irrelevant; catalog numbers are not like scores flashed by Olympic judges, with higher numbers going to better courses. Another difference is that in large state universities the graduate students tend to have much more exposure to the faculty than do the undergraduate students—their classes are much smaller and are more frequently taught by the regular faculty members. This is relevant, since student exposure to faculty can contribute powerfully to academic excellence. The conclusion may still be true. But even though this argument does well on the first condition, it performs badly on the second and so its logic must be considered weak.

EXERCISES Chapter 15, set (c)

For each of the arguments in set (a), do three things: ( i ) state an irrelevant dissimilarity, and explain, ( ii ) explain any relevant dissimilarities, and ( iii ) state your evaluation of the argument’s logic based on this and the previous exercise.

Sample answer. ( i ) The basketball program probably has a higher proportion of students on full scholarship than does the English department. This doesn’t seem relevant, since it doesn’t make English a better candidate for preservation in the face of difficulties. ( ii ) The most important dissimilarity is that the English department is not only an academic program, but also one that is central to the mission of the institution, while the basketball program is an athletic program and thus more peripheral to its mission. This means there is a far stronger impetus to work out English department difficulties before disbanding it. ( iii ) Though the argument is OK on the first part of the total evidence condition, it fails the second part and is logically very weak.

15.4 The Special Character of Arguments from Analogy

15.4.1 arguments from analogy as logical borrowers.

As you may have noticed, every example of an argument from analogy worked out in this chapter has been declared logically weak and thus unsound. This is not an aberration. Although not all arguments from analogy are unsound, they do establish their conclusions far less often than any other sort of argument. Plato, in the lead quotation for this chapter, calls them “impostors.” Analogical arguments, unlike any other arguments we look at in this book, have a built-in logical shortcoming.

Let’s take another look at the logical form of arguments from analogy:

• A (basic analog) is F (basic similarity) and G (inferred similarity).
• B (inferred analog) is F (basic similarity).
• ∴ B (inferred analog) is G (inferred similarity).

What is the source of logical strength for such an argument? Not the correct form condition; as with every other inductive argument, satisfying this condition merely qualifies the argument for any strength that might be conferred by the total evidence condition. Not the second part of the total evidence condition; the absence of relevant dissimilarities simply means there is no evidence to undermine whatever strength it has. [2]  This leaves the first part of the total evidence condition as the sole positive source of logical strength.

How does the first part of the total evidence condition provide logical strength? By virtue of the fact that the basic similarity counts in favor of the inferred similarity. But what does count in favor of mean here? The only meaning I know is a sound argument can be offered for it. So we can now see that logically strong analogical arguments derive their logical strength from another argument—the argument that can be offered from the inferred similarity to the basic similarity. We will call such an argument (an argument from F to G —see premise 1 of the form clarified above) a background argument . Stated simply: an analogical argument’s only logical strength is borrowed from a background argument.

Any other sort of argument can, in principle, lend its strength to an argument from analogy. For example, in the preceding chapter we looked briefly at the argument Every Japanese car I’ve ever owned has been well built, so that Toyota is probably well built. It could easily be clarified as an argument from analogy, clarified as follows:

• Every Japanese car I’ve ever owned has been a Japanese car and has been well built.
• [That Toyota is a Japanese car.]
• ∴ That Toyota is well built.

If the similarity is relevant in this case, it is because the background argument is a logically strong inductive generalization that goes from my experience of Japanese cars (the basic similarity) to the conclusion that Japanese cars in general are well built (the inferred similarity). The argument from analogy is logical only if this generalization works. So it borrows its logical strength from an inductive generalization.

The next passage, from Science News, provides a second example of borrowed logic in an argument from analogy.

The concept of “vintage year” took on a new meaning this week when two scientists presented the first chemical evidence that wine existed as far back as about 3500 bc. They had noticed a red stain while piecing together jars excavated from an Iranian site. They compared the stain with a similar stain in an ancient Egyptian vessel known to have contained wine. The researchers scraped the reddish residue from the jars and analyzed the samples with infrared spectroscopy. Residues from the Iranian and Egyptian jars looked alike and were full of tartaric acid, a chemical naturally abundant only in grapes. “Those crystals are a signature for wine,” says one researcher.

The argument can be clarified thus:

• The Egyptian jar had a certain red stain and contained wine.
• The Iranian jar had the same red stain.
• ∴ That Iranian jar contained wine.

In this case, if the similarity is relevant it is because the background argument is a sound explanatory argument (of a sort we will cover thoroughly in the next chapter) that establishes that the red stains (the basic similarity) have properties that are best explained as caused by wine (the inferred similarity). This argument’s logical strength is borrowed from an explanatory argument.

As a final example, arguments from analogy can even borrow their logical strength from deductive arguments. Consider the validity counterexamples of Chapter 10. In that chapter we started with an inverted—and invalid—Socrates argument:

• All men are mortal.
• Socrates is mortal.
• ∴ Socrates is a man.

We then offered as a validity counterexample this obviously invalid (because of true premises and false conclusion) Atlantic argument:

• All ponds are bodies of water.
• The Atlantic Ocean is a body of water.
• ∴ The Atlantic Ocean is a pond.

In this way we saw that the Socrates argument was invalid. Like any validity counterexample, the reasoning can be represented as an argument from analogy, clarified as follows:

• The Atlantic argument has a certain form and is invalid.
• The Socrates argument has the same form.
• ∴ The Socrates argument is invalid.

Here the relevance of the similarity depends on a deductive background argument; for the way to argue that a certain form (the basic similarity) is invalid (the inferred similarity) is by use of this valid affirming the antecedent argument, which has a self-evidently true first premise:

• If the form of an argument is such that it is possible for the premises to be true and the conclusion false, then the argument is invalid.
• This particular form is such that it is possible for the premises to be true and the conclusion false.
• ∴ The argument is invalid.

In this case, the logical strength of the analogical argument is borrowed from a sound deduction.

By its very nature, then, when an analogical argument works it works on borrowed logic. The two analogs mainly serve to get in the way by providing a basis for relevant dissimilarities. It is the background argument, which ignores the analogs and is concerned solely with the basic and inferred similarities, that serves as the argument’s motor. In the end, the background argument cannot itself be some other argument from analogy, since the background argument would depend on a background argument (and so on).

There are two practical lessons here. First, if you can see what the background argument is, bring it to the foreground when you clarify the argument, abandoning the analogical form. The Toyota argument, for example, would be much easier to evaluate properly if clarified as a complex argument composed of an inductive generalization and a frequency argument (as illustrated in Chapter 14); and the Iranian jar argument, likewise, if paraphrased as an explanatory argument. Second, if you cannot see what the background argument is, you should normally resist the temptation to judge it as logically strong until you better understand the background argument. As noted at the beginning of the chapter, analogical arguments are custom-made for the way our minds work, which makes them extraordinarily persuasive. But their inherent reliance on logical borrowing also makes them very good at concealing logical defects. When a persuasive car salesman won’t let you open the hood to inspect the motor, it may be prudent to shop elsewhere.

15.4.2 Arguments from Analogy as Psychological Lenders

From a logical point of view, analogical arguments are borrowers. But from a psychological point of view, they often put other arguments deeply into their debt. They can hint as well as hide.

Look, for example, at the Iranian jar argument. The analogy between the two stains is what suggested to the researchers that the jar had once contained wine. This set in motion a research effort in which samples scraped from both jars were examined by infrared spectroscopy, revealing crystals that were “a signature for wine.” One could perhaps say that this new evidence converts the initial analogical argument from a merely suggestive one into a logically strong one, by showing just how relevant the basic similarity (same red stain) is to the inferred similarity (that it contained wine). But it would be much clearer to simply say that the background argument displaces the argument from analogy. Analogical reasoning has lent a powerful psychological boost to the research program by producing the suggestive idea. Still, any logical strength it gains from that research program is borrowed from the background argument—that is, from the explanatory argument about crystals developed by the researchers. Clarity is increased if the initial analogy drops out of any account of the logical support for the conclusion—as long as it remains as a central feature of the history of the discovery. [3]

Analogical arguments can lend a valuable psychological boost to inquiry of every sort. Consider the free speech argument. Even if you are not persuaded by the proposed analogy between shouting fire and distributing leaflets, it is certainly suggestive. In particular, it suggests that you are wrong if you think that all expressions are protected. Further, it suggests a way of reasoning about which ones are not protected—namely, by thinking about the possible dangers caused by the speech in question. If that way of reasoning succeeds, the argument from analogy gets psychological credit for suggesting it, even if it gets no logical credit for supporting it.

Nineteenth-century philosopher John Stuart Mill aptly declared that good reasoners will consider any analogical argument as a “guidepost, pointing out the direction in which more rigorous investigations should be prosecuted.” Arguments from analogy brilliantly serve a necessary function in reasoning. We would be lost without good guideposts. But we should not confuse them with destinations.

EXERCISES Chapter 15, set (d)

Fully clarify and evaluate each of the arguments from analogy. In cases where you can see the background argument, you may clarify and evaluate either the analogical argument or the background argument.

• I’ve only seen one Hitchcock movie— Psycho. It was scary. Let’s try The Birds. I bet it will be scary too.
• To solve our drug problems, instead of outlawing drugs we must make them as safe and risk-free and—yes—as healthy as possible. It’s like sex. We recognize that people will continue to have sex for nonreproductive reasons, whatever the laws, and with that in mind we try to make sexual practices as safe as possible in order to minimize the spread of the sexually transmitted diseases.
• Question (investigator, to a university president): “Your administration will undertake reviews or investigations of members of your faculty without their being informed of the fact?”

A:  “I believe it’s very possible. I believe it happened in this case.”

Q:  “Do you consider that proper and appropriate?”

A:  “Personal opinion? Yes.”

Q: “Can you tell me why?”

A:  “I don’t know. Why not? I guess in an analogy, I don’t think J. Edgar Hoover, for example, ever advised everybody he was investigating that they were being investigated.”

Q:  “But he, J. Edgar Hoover, wasn’t running a university.”— Lingua Franca

• Breceda and lifeguards up and down the beach stressed the dangers of sleeping on the beach at night. “The people who get hurt are pretty much innocent,” Breceda said. “They take a walk on the beach at Puerto Vallarta at 3 a.m. and nothing happens, and so they assume it’s OK to do it here. But a whole different situation occurs here.” In addition to the dangers posed by muggers and rapists, people sleeping on the beach also could get run over by sweepers. — Los Angeles Times (Consider the argument attributed to the people who sleep on the beach.)
• “ Question: Surely society has a right to rid itself of a man like Ted Bundy? Answer : My main opposition to the death penalty is what it does to society. Our society kills people in cages. It is like going hunting in a zoo. In the cage they are not dangerous, but executing them is very dangerous—for us.” —I. Gray and M. Stanley, eds., A Punishment in Search of a Crime: Americans Speak Out Against the Death Penalty
• “At their August 1945 Potsdam meeting, Truman remarked to an aide, ‘Stalin is as near like Tom Pendergast as any man I know.’ Pendergast was a Missouri machine boss who helped get Truman elected to the Senate. For some superficial reason Truman concluded that, like Pendergast, Stalin was a man one could deal with, a man of his word. ‘It led Truman to believe that Stalin would hold free elections in Eastern Europe,’ says Deborah Larson, a UCLA political scientist.” — Associated Press
• Gerry Spence is serving as the pro bono defense attorney for an “environmental terrorist” who embedded metal plates in trees so that the bulldozers would be wrecked (and, potentially, the drivers injured). He is asked if “monkeywrenching” trees is ever justified. Spence’s sleight-of-hand answer reveals why he wins so many cases: “In most circumstances, breaking the law is improper. Now, suppose a tractor is about to run over a child. Is it improper to demolish the tractor? Suppose the tractor was going to run over something inanimate, a painting by Van Gogh that cost $32 million. Now, what about a tractor running down a tree? A 400-year-old original growth tree?” — Forbes
• “Thoughtful and right-minded men place their homage and consideration for woman upon an instinctive consciousness that her unmasculine qualities, whether called weaknesses, frailties, or what we will, are the sources of her characteristic and a special strength within the area of her legitimate endeavor. In actual war, it is the men who go to battle, enduring hardship and privation and suffering disease and death for the cause they follow. It is the mothers, wives, and maids betrothed, who neither following the camp nor fighting in battle, constitute at home an army of woman’s constancy and love whose yearning hearts make men brave and patriotic. So, in political warfare, it is perfectly fitting that actual strife and battle would be apportioned to men, and that the influence of woman, radiating from the homes of our land, should inspire to lofty aims and purposes those who struggle for the right.” —Grover Cleveland, Ladies Home Journal, 1905
• One philosopher, arguing that the rights of a rape victim to make decisions about her body can be more important than the right to life of a fetus, develops the following analogy: “Let me ask you to imagine this. You wake up in the morning and find yourself back to back in bed with an unconscious violinist. A famous unconscious violinist. He has been found to have a fatal kidney ailment, and the Society of Music Lovers has canvassed all the available medical records and found that you alone have the right blood type to help. They have therefore kidnapped you, and last night the violinist’s circulatory system was plugged into yours, so that your kidneys can be used to extract poisons from his blood as well as your own. The director of the hospital now tells you, ‘Look, we’re sorry the Society of Music Lovers did this to you—we would never have permitted it if we had known. But still, they did it, and the violinist now is plugged into you. To unplug you would be to kill him. But never mind, it’s only for nine months. By then he will have recovered from his ailment, and can safely be unplugged from you.’ Is it morally incumbent on you to accede to this situation?” —Judith Jarvis Thompson, Philosophy and Public Affairs
• “Look round the world. Contemplate the whole and every part of it. You will find it to be like one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines and their parts are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. From this we can see that the curious adapting of means to ends throughout all nature resembles exactly, though it much exceeds, the adapting of means to ends in the things made by human beings. Since, therefore, the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble, and that there is an Author of Nature who is somewhat similar to the mind of man, though possessed of much larger faculties, proportioned to the grandeur of the work which he has executed. Therefore we prove at once the existence of God and his similarity to human mind and intelligence.” —David Hume, Dialogues Concerning Natural Religion

15.5 Summary of Chapter Fifteen

Arguments from analogy typically contend that because two items are the same in one respect, they are the same in another respect. The basic analog is compared to the inferred analog; because they have the basic similarity in common, it is concluded that the inferred analog also has the inferred similarity.

The total evidence condition has two parts. First, the basic similarity must be relevant—that is, it must count toward the presence of the inferred similarity. Second, there must not be any dissimilarities that are relevant—that is, any dissimilarity between the two analogs must not make the basic analog a better candidate for the inferred property. The argument is logically weaker to the extent that it fails in either of these two areas.

Their only positive logical strength comes from the background argument that establishes that the inferred similarity follows from the basic similarity; thus, whatever logical success analogical arguments have is borrowed. This makes it especially important to pay close attention to the first part of the total evidence condition. On the other hand, analogical arguments play an important psychological role in suggesting lines of reasoning, and so should be cultivated for that purpose.

15.6 Guidelines for Chapter Fifteen

• Structure arguments from analogy, when it would be loyal to do so, by identifying four things—the basic and inferred analogs and the basic and inferred similarities—then inserting each into its proper place in the form. Remember that the second premise, which declares the basic similarity, is often implicit.
• In considering whether an argument from analogy has satisfied the total evidence condition, first ask, Is the basic similarity relevant? To answer this question, look at the extent to which the basic similarity counts in favor of the inferred similarity.
• When the basic similarity is described by a general term, consider whether its meaning shifts from one use to the next. If it shifts enough to affect the soundness of the argument, revise your clarification to eliminate the ambiguity.
• In considering whether an argument from analogy has satisfied the total evidence condition, ask next, Are any of the dissimilarities relevant? To answer this question, look at the extent to which any dissimilarity makes the basic analog a better candidate than the inferred analog for the inferred property.
• When you can clearly see the background argument, clarify it rather than the argument from analogy. When you cannot see the background argument, you should normally reserve final judgment about the strength of the argument’s logic.

15.7 Glossary for Chapter Fifteen

Analogs —the two things (or classes of things) that are said to be similar in an argument from analogy.

Argument from analogy —an argument that asserts that because two items are the same in one respect, they are the same in another respect. They can be represented by this form:

Background argument —an argument that shows that the inferred similarity (of an analogical argument) follows from the basic similarity—that is, an argument that shows that the basic similarity is relevant.

Basic analog —in an argument from analogy, the item that we are presumably more familiar with, which is presumably known to have both the basic and the inferred similarities.

Basic similarity —in an argument from analogy, the property that the two analogs share, presumably without controversy.

Fallacy of false analogy —the mistake of using an argument from analogy in which the basic similarity is not relevant or in which there are relevant dissimilarities between the basic and inferred analogs. Because this term says nothing about what precisely has gone wrong with the argument, it is better to explain more specifically how it is that some necessary condition for soundness has not been satisfied. Also called the fallacy of faulty analogy.

Inferred analog —in an argument from analogy, the item in question, about which the argument is drawing its conclusion.

Inferred similarity —in an argument from analogy, the property that the inferred analog is alleged to have because the basic analog has it.

• The British usually spell it analogue . Historically, the term was analogon . ↵
• The second part of the total evidence condition for frequency arguments operates the same way. ↵
• To use terminology mentioned elsewhere in the text, it is important in the context of discovery, but not in the context of justification. ↵

An argument that asserts that because two items are the same in one respect, they are the same in another respect. They can be represented by this form:

1. A is F and G. 2. B is F. ∴ C . B is G.

The two things (or classes of things) that are said to be similar in an argument from analogy.

In an argument from analogy, the item that we are presumably more familiar with, which is presumably known to have both the basic and the inferred similarities.

In an argument from analogy, the item in question, about which the argument is drawing its conclusion.

In an argument from analogy, the property that the two analogs share, presumably without controversy.

In an argument from analogy, the property that the inferred analog is alleged to have because the basic analog has it.

The mistake of using an argument from analogy in which the basic similarity is not relevant or in which there are relevant dissimilarities between the basic and inferred analogs. Because this term says nothing about what precisely has gone wrong with the argument, it is better to explain more specifically how it is that some necessary condition for soundness has not been satisfied. Also called the fallacy of faulty analogy.

An argument that shows that the inferred similarity (of an analogical argument) follows from the basic similarity—that is, an argument that shows that the basic similarity is relevant.

A Guide to Good Reasoning: Cultivating Intellectual Virtues Copyright © 2020 by David Carl Wilson is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Analogy and Analogical Reasoning

An analogy is a comparison between two objects, or systems of objects, that highlights respects in which they are thought to be similar. Analogical reasoning is any type of thinking that relies upon an analogy. An analogical argument is an explicit representation of a form of analogical reasoning that cites accepted similarities between two systems to support the conclusion that some further similarity exists. In general (but not always), such arguments belong in the category of ampliative reasoning, since their conclusions do not follow with certainty but are only supported with varying degrees of strength. However, the proper characterization of analogical arguments is subject to debate (see §2.2 ).

Analogical reasoning is fundamental to human thought and, arguably, to some nonhuman animals as well. Historically, analogical reasoning has played an important, but sometimes mysterious, role in a wide range of problem-solving contexts. The explicit use of analogical arguments, since antiquity, has been a distinctive feature of scientific, philosophical and legal reasoning. This article focuses primarily on the nature, evaluation and justification of analogical arguments. Related topics include metaphor , models in science , and precedent and analogy in legal reasoning .

1. Introduction: the many roles of analogy

2.1 examples, 2.2 characterization, 2.3 plausibility, 2.4 analogical inference rules, 3.1 commonsense guidelines, 3.2 aristotle’s theory, 3.3 material criteria: hesse’s theory, 3.4 formal criteria: the structure-mapping theory, 3.5 other theories, 3.6 practice-based approaches, 4.1 deductive justification, 4.2 inductive justification, 4.3 a priori justification, 4.4 pragmatic justification, 5.1 analogy and confirmation, 5.2 conceptual change and theory development, online manuscript, related entries.

Analogies are widely recognized as playing an important heuristic role, as aids to discovery. They have been employed, in a wide variety of settings and with considerable success, to generate insight and to formulate possible solutions to problems. According to Joseph Priestley, a pioneer in chemistry and electricity,

analogy is our best guide in all philosophical investigations; and all discoveries, which were not made by mere accident, have been made by the help of it. (1769/1966: 14)

Priestley may be over-stating the case, but there is no doubt that analogies have suggested fruitful lines of inquiry in many fields. Because of their heuristic value, analogies and analogical reasoning have been a particular focus of AI research. Hájek (2018) examines analogy as a heuristic tool in philosophy.

Example 1 . Hydrodynamic analogies exploit mathematical similarities between the equations governing ideal fluid flow and torsional problems. To predict stresses in a planned structure, one can construct a fluid model, i.e., a system of pipes through which water passes (Timoshenko and Goodier 1970). Within the limits of idealization, such analogies allow us to make demonstrative inferences, for example, from a measured quantity in the fluid model to the analogous value in the torsional problem. In practice, there are numerous complications (Sterrett 2006).

At the other extreme, an analogical argument may provide very weak support for its conclusion, establishing no more than minimal plausibility. Consider:

Example 2 . Thomas Reid’s (1785) argument for the existence of life on other planets (Stebbing 1933; Mill 1843/1930; Robinson 1930; Copi 1961). Reid notes a number of similarities between Earth and the other planets in our solar system: all orbit and are illuminated by the sun; several have moons; all revolve on an axis. In consequence, he concludes, it is “not unreasonable to think, that those planets may, like our earth, be the habitation of various orders of living creatures” (1785: 24).

Such modesty is not uncommon. Often the point of an analogical argument is just to persuade people to take an idea seriously. For instance:

Example 3 . Darwin takes himself to be using an analogy between artificial and natural selection to argue for the plausibility of the latter:

Why may I not invent the hypothesis of Natural Selection (which from the analogy of domestic productions, and from what we know of the struggle of existence and of the variability of organic beings, is, in some very slight degree, in itself probable) and try whether this hypothesis of Natural Selection does not explain (as I think it does) a large number of facts…. ( Letter to Henslow , May 1860 in Darwin 1903)

Here it appears, by Darwin’s own admission, that his analogy is employed to show that the hypothesis is probable to some “slight degree” and thus merits further investigation. Some, however, reject this characterization of Darwin’s reasoning (Richards 1997; Gildenhuys 2004).

Sometimes analogical reasoning is the only available form of justification for a hypothesis. The method of ethnographic analogy is used to interpret

the nonobservable behaviour of the ancient inhabitants of an archaeological site (or ancient culture) based on the similarity of their artifacts to those used by living peoples. (Hunter and Whitten 1976: 147)

For example:

Example 4 . Shelley (1999, 2003) describes how ethnographic analogy was used to determine the probable significance of odd markings on the necks of Moche clay pots found in the Peruvian Andes. Contemporary potters in Peru use these marks (called sígnales ) to indicate ownership; the marks enable them to reclaim their work when several potters share a kiln or storage facility. Analogical reasoning may be the only avenue of inference to the past in such cases, though this point is subject to dispute (Gould and Watson 1982; Wylie 1982, 1985). Analogical reasoning may have similar significance for cosmological phenomena that are inaccessible due to limits on observation (Dardashti et al. 2017). See §5.1 for further discussion.

As philosophers and historians such as Kuhn (1996) have repeatedly pointed out, there is not always a clear separation between the two roles that we have identified, discovery and justification. Indeed, the two functions are blended in what we might call the programmatic (or paradigmatic ) role of analogy: over a period of time, an analogy can shape the development of a program of research. For example:

Example 5 . An ‘acoustical analogy’ was employed for many years by certain nineteenth-century physicists investigating spectral lines. Discrete spectra were thought to be

completely analogous to the acoustical situation, with atoms (and/or molecules) serving as oscillators originating or absorbing the vibrations in the manner of resonant tuning forks. (Maier 1981: 51)

Guided by this analogy, physicists looked for groups of spectral lines that exhibited frequency patterns characteristic of a harmonic oscillator. This analogy served not only to underwrite the plausibility of conjectures, but also to guide and limit discovery by pointing scientists in certain directions.

More generally, analogies can play an important programmatic role by guiding conceptual development (see §5.2 ). In some cases, a programmatic analogy culminates in the theoretical unification of two different areas of inquiry.

Example 6 . Descartes’s (1637/1954) correlation between geometry and algebra provided methods for systematically handling geometrical problems that had long been recognized as analogous. A very different relationship between analogy and discovery exists when a programmatic analogy breaks down, as was the ultimate fate of the acoustical analogy. That atomic spectra have an entirely different explanation became clear with the advent of quantum theory. In this case, novel discoveries emerged against background expectations shaped by the guiding analogy. There is a third possibility: an unproductive or misleading programmatic analogy may simply become entrenched and self-perpetuating as it leads us to “construct… data that conform to it” (Stepan 1996: 133). Arguably, the danger of this third possibility provides strong motivation for developing a critical account of analogical reasoning and analogical arguments.

Analogical cognition , which embraces all cognitive processes involved in discovering, constructing and using analogies, is broader than analogical reasoning (Hofstadter 2001; Hofstadter and Sander 2013). Understanding these processes is an important objective of current cognitive science research, and an objective that generates many questions. How do humans identify analogies? Do nonhuman animals use analogies in ways similar to humans? How do analogies and metaphors influence concept formation?

This entry, however, concentrates specifically on analogical arguments. Specifically, it focuses on three central epistemological questions:

• What criteria should we use to evaluate analogical arguments?
• What philosophical justification can be provided for analogical inferences?
• How do analogical arguments fit into a broader inferential context (i.e., how do we combine them with other forms of inference), especially theoretical confirmation?

Following a preliminary discussion of the basic structure of analogical arguments, the entry reviews selected attempts to provide answers to these three questions. To find such answers would constitute an important first step towards understanding the nature of analogical reasoning. To isolate these questions, however, is to make the non-trivial assumption that there can be a theory of analogical arguments —an assumption which, as we shall see, is attacked in different ways by both philosophers and cognitive scientists.

2. Analogical arguments

Analogical arguments vary greatly in subject matter, strength and logical structure. In order to appreciate this variety, it is helpful to increase our stock of examples. First, a geometric example:

Example 7 (Rectangles and boxes). Suppose that you have established that of all rectangles with a fixed perimeter, the square has maximum area. By analogy, you conjecture that of all boxes with a fixed surface area, the cube has maximum volume.

Two examples from the history of science:

Example 8 (Morphine and meperidine). In 1934, the pharmacologist Schaumann was testing synthetic compounds for their anti-spasmodic effect. These drugs had a chemical structure similar to morphine. He observed that one of the compounds— meperidine , also known as Demerol —had a physical effect on mice that was previously observed only with morphine: it induced an S-shaped tail curvature. By analogy, he conjectured that the drug might also share morphine’s narcotic effects. Testing on rats, rabbits, dogs and eventually humans showed that meperidine, like morphine, was an effective pain-killer (Lembeck 1989: 11; Reynolds and Randall 1975: 273).

Example 9 (Priestley on electrostatic force). In 1769, Priestley suggested that the absence of electrical influence inside a hollow charged spherical shell was evidence that charges attract and repel with an inverse square force. He supported his hypothesis by appealing to the analogous situation of zero gravitational force inside a hollow shell of uniform density.

Finally, an example from legal reasoning:

Example 10 (Duty of reasonable care). In a much-cited case ( Donoghue v. Stevenson 1932 AC 562), the United Kingdom House of Lords found the manufacturer of a bottle of ginger beer liable for damages to a consumer who became ill as a result of a dead snail in the bottle. The court argued that the manufacturer had a duty to take “reasonable care” in creating a product that could foreseeably result in harm to the consumer in the absence of such care, and where the consumer had no possibility of intermediate examination. The principle articulated in this famous case was extended, by analogy, to allow recovery for harm against an engineering firm whose negligent repair work caused the collapse of a lift ( Haseldine v. CA Daw & Son Ltd. 1941 2 KB 343). By contrast, the principle was not applicable to a case where a workman was injured by a defective crane, since the workman had opportunity to examine the crane and was even aware of the defects ( Farr v. Butters Brothers & Co. 1932 2 KB 606).

What, if anything, do all of these examples have in common? We begin with a simple, quasi-formal characterization. Similar formulations are found in elementary critical thinking texts (e.g., Copi and Cohen 2005) and in the literature on argumentation theory (e.g., Govier 1999, Guarini 2004, Walton and Hyra 2018). An analogical argument has the following form:

• \(S\) is similar to \(T\) in certain (known) respects.
• \(S\) has some further feature \(Q\).
• Therefore, \(T\) also has the feature \(Q\), or some feature \(Q^*\) similar to \(Q\).

(1) and (2) are premises. (3) is the conclusion of the argument. The argument form is ampliative ; the conclusion is not guaranteed to follow from the premises.

\(S\) and \(T\) are referred to as the source domain and target domain , respectively. A domain is a set of objects, properties, relations and functions, together with a set of accepted statements about those objects, properties, relations and functions. More formally, a domain consists of a set of objects and an interpreted set of statements about them. The statements need not belong to a first-order language, but to keep things simple, any formalizations employed here will be first-order. We use unstarred symbols \((a, P, R, f)\) to refer to items in the source domain and starred symbols \((a^*, P^*, R^*, f^*)\) to refer to corresponding items in the target domain. In Example 9 , the source domain items pertain to gravitation; the target items pertain to electrostatic attraction.

Formally, an analogy between \(S\) and \(T\) is a one-to-one mapping between objects, properties, relations and functions in \(S\) and those in \(T\). Not all of the items in \(S\) and \(T\) need to be placed in correspondence. Commonly, the analogy only identifies correspondences between a select set of items. In practice, we specify an analogy simply by indicating the most significant similarities (and sometimes differences).

We can improve on this preliminary characterization of the argument from analogy by introducing the tabular representation found in Hesse (1966). We place corresponding objects, properties, relations and propositions side-by-side in a table of two columns, one for each domain. For instance, Reid’s argument ( Example 2 ) can be represented as follows (using \(\Rightarrow\) for the analogical inference):

Hesse introduced useful terminology based on this tabular representation. The horizontal relations in an analogy are the relations of similarity (and difference) in the mapping between domains, while the vertical relations are those between the objects, relations and properties within each domain. The correspondence (similarity) between earth’s having a moon and Mars’ having moons is a horizontal relation; the causal relation between having a moon and supporting life is a vertical relation within the source domain (with the possibility of a distinct such relation existing in the target as well).

In an earlier discussion of analogy, Keynes (1921) introduced some terminology that is also helpful.

Positive analogy . Let \(P\) stand for a list of accepted propositions \(P_1 , \ldots ,P_n\) about the source domain \(S\). Suppose that the corresponding propositions \(P^*_1 , \ldots ,P^*_n\), abbreviated as \(P^*\), are all accepted as holding for the target domain \(T\), so that \(P\) and \(P^*\) represent accepted (or known) similarities. Then we refer to \(P\) as the positive analogy .

Negative analogy . Let \(A\) stand for a list of propositions \(A_1 , \ldots ,A_r\) accepted as holding in \(S\), and \(B^*\) for a list \(B_1^*, \ldots ,B_s^*\) of propositions holding in \(T\). Suppose that the analogous propositions \(A^* = A_1^*, \ldots ,A_r^*\) fail to hold in \(T\), and similarly the propositions \(B = B_1 , \ldots ,B_s\) fail to hold in \(S\), so that \(A, {\sim}A^*\) and \({\sim}B, B^*\) represent accepted (or known) differences. Then we refer to \(A\) and \(B\) as the negative analogy .

Neutral analogy . The neutral analogy consists of accepted propositions about \(S\) for which it is not known whether an analogue holds in \(T\).

Finally we have:

Hypothetical analogy . The hypothetical analogy is simply the proposition \(Q\) in the neutral analogy that is the focus of our attention.

These concepts allow us to provide a characterization for an individual analogical argument that is somewhat richer than the original one.

An analogical argument may thus be summarized:

It is plausible that \(Q^*\) holds in the target, because of certain known (or accepted) similarities with the source domain, despite certain known (or accepted) differences.

In order for this characterization to be meaningful, we need to say something about the meaning of ‘plausibly.’ To ensure broad applicability over analogical arguments that vary greatly in strength, we interpret plausibility rather liberally as meaning ‘with some degree of support’. In general, judgments of plausibility are made after a claim has been formulated, but prior to rigorous testing or proof. The next sub-section provides further discussion.

Note that this characterization is incomplete in a number of ways. The manner in which we list similarities and differences, the nature of the correspondences between domains: these things are left unspecified. Nor does this characterization accommodate reasoning with multiple analogies (i.e., multiple source domains), which is ubiquitous in legal reasoning and common elsewhere. To characterize the argument form more fully, however, is not possible without either taking a step towards a substantive theory of analogical reasoning or restricting attention to certain classes of analogical arguments.

Arguments by analogy are extensively discussed within argumentation theory. There is considerable debate about whether they constitute a species of deductive inference (Govier 1999; Waller 2001; Guarini 2004; Kraus 2015). Argumentation theorists also make use of tools such as speech act theory (Bermejo-Luque 2012), argumentation schemes and dialogue types (Macagno et al. 2017; Walton and Hyra 2018) to distinguish different types of analogical argument.

Arguments by analogy are also discussed in the vast literature on scientific models and model-based reasoning, following the lead of Hesse (1966). Bailer-Jones (2002) draws a helpful distinction between analogies and models. While “many models have their roots in an analogy” (2002: 113) and analogy “can act as a catalyst to aid modeling,” Bailer-Jones observes that “the aim of modeling has nothing intrinsically to do with analogy.” In brief, models are tools for prediction and explanation, whereas analogical arguments aim at establishing plausibility. An analogy is evaluated in terms of source-target similarity, while a model is evaluated on how successfully it “provides access to a phenomenon in that it interprets the available empirical data about the phenomenon.” If we broaden our perspective beyond analogical arguments , however, the connection between models and analogies is restored. Nersessian (2009), for instance, stresses the role of analog models in concept-formation and other cognitive processes.

To say that a hypothesis is plausible is to convey that it has epistemic support: we have some reason to believe it, even prior to testing. An assertion of plausibility within the context of an inquiry typically has pragmatic connotations as well: to say that a hypothesis is plausible suggests that we have some reason to investigate it further. For example, a mathematician working on a proof regards a conjecture as plausible if it “has some chances of success” (Polya 1954 (v. 2): 148). On both points, there is ambiguity as to whether an assertion of plausibility is categorical or a matter of degree. These observations point to the existence of two distinct conceptions of plausibility, probabilistic and modal , either of which may reflect the intended conclusion of an analogical argument.

On the probabilistic conception, plausibility is naturally identified with rational credence (rational subjective degree of belief) and is typically represented as a probability. A classic expression may be found in Mill’s analysis of the argument from analogy in A System of Logic :

There can be no doubt that every resemblance [not known to be irrelevant] affords some degree of probability, beyond what would otherwise exist, in favour of the conclusion. (Mill 1843/1930: 333)

In the terminology introduced in §2.2, Mill’s idea is that each element of the positive analogy boosts the probability of the conclusion. Contemporary ‘structure-mapping’ theories ( §3.4 ) employ a restricted version: each structural similarity between two domains contributes to the overall measure of similarity, and hence to the strength of the analogical argument.

On the alternative modal conception, ‘it is plausible that \(p\)’ is not a matter of degree. The meaning, roughly speaking, is that there are sufficient initial grounds for taking \(p\) seriously, i.e., for further investigation (subject to feasibility and interest). Informally: \(p\) passes an initial screening procedure. There is no assertion of degree. Instead, ‘It is plausible that’ may be regarded as an epistemic modal operator that aims to capture a notion, prima facie plausibility, that is somewhat stronger than ordinary epistemic possibility. The intent is to single out \(p\) from an undifferentiated mass of ideas that remain bare epistemic possibilities. To illustrate: in 1769, Priestley’s argument ( Example 9 ), if successful, would establish the prima facie plausibility of an inverse square law for electrostatic attraction. The set of epistemic possibilities—hypotheses about electrostatic attraction compatible with knowledge of the day—was much larger. Individual analogical arguments in mathematics (such as Example 7 ) are almost invariably directed towards prima facie plausibility.

The modal conception figures importantly in some discussions of analogical reasoning. The physicist N. R. Campbell (1957) writes:

But in order that a theory may be valuable it must … display an analogy. The propositions of the hypothesis must be analogous to some known laws…. (1957: 129)

Commenting on the role of analogy in Fourier’s theory of heat conduction, Campbell writes:

Some analogy is essential to it; for it is only this analogy which distinguishes the theory from the multitude of others… which might also be proposed to explain the same laws. (1957: 142)

The interesting notion here is that of a “valuable” theory. We may not agree with Campbell that the existence of analogy is “essential” for a novel theory to be “valuable.” But consider the weaker thesis that an acceptable analogy is sufficient to establish that a theory is “valuable”, or (to qualify still further) that an acceptable analogy provides defeasible grounds for taking the theory seriously. (Possible defeaters might include internal inconsistency, inconsistency with accepted theory, or the existence of a (clearly superior) rival analogical argument.) The point is that Campbell, following the lead of 19 th century philosopher-scientists such as Herschel and Whewell, thinks that analogies can establish this sort of prima facie plausibility. Snyder (2006) provides a detailed discussion of the latter two thinkers and their ideas about the role of analogies in science.

In general, analogical arguments may be directed at establishing either sort of plausibility for their conclusions; they can have a probabilistic use or a modal use. Examples 7 through 9 are best interpreted as supporting modal conclusions. In those arguments, an analogy is used to show that a conjecture is worth taking seriously. To insist on putting the conclusion in probabilistic terms distracts attention from the point of the argument. The conclusion might be modeled (by a Bayesian) as having a certain probability value because it is deemed prima facie plausible, but not vice versa. Example 2 , perhaps, might be regarded as directed primarily towards a probabilistic conclusion.

There should be connections between the two conceptions. Indeed, we might think that the same analogical argument can establish both prima facie plausibility and a degree of probability for a hypothesis. But it is difficult to translate between epistemic modal concepts and probabilities (Cohen 1980; Douven and Williamson 2006; Huber 2009; Spohn 2009, 2012). We cannot simply take the probabilistic notion as the primitive one. It seems wise to keep the two conceptions of plausibility separate.

Schema (4) is a template that represents all analogical arguments, good and bad. It is not an inference rule. Despite the confidence with which particular analogical arguments are advanced, nobody has ever formulated an acceptable rule, or set of rules, for valid analogical inferences. There is not even a plausible candidate. This situation is in marked contrast not only with deductive reasoning, but also with elementary forms of inductive reasoning, such as induction by enumeration.

Of course, it is difficult to show that no successful analogical inference rule will ever be proposed. But consider the following candidate, formulated using the concepts of schema (4) and taking us only a short step beyond that basic characterization.

Rule (5) is modeled on the straight rule for enumerative induction and inspired by Mill’s view of analogical inference, as described in §2.3. We use the generic phrase ‘degree of support’ in place of probability, since other factors besides the analogical argument may influence our probability assignment for \(Q^*\).

It is pretty clear that (5) is a non-starter. The main problem is that the rule justifies too much. The only substantive requirement introduced by (5) is that there be a nonempty positive analogy. Plainly, there are analogical arguments that satisfy this condition but establish no prima facie plausibility and no measure of support for their conclusions.

Here is a simple illustration. Achinstein (1964: 328) observes that there is a formal analogy between swans and line segments if we take the relation ‘has the same color as’ to correspond to ‘is congruent with’. Both relations are reflexive, symmetric, and transitive. Yet it would be absurd to find positive support from this analogy for the idea that we are likely to find congruent lines clustered in groups of two or more, just because swans of the same color are commonly found in groups. The positive analogy is antecedently known to be irrelevant to the hypothetical analogy. In such a case, the analogical inference should be utterly rejected. Yet rule (5) would wrongly assign non-zero degree of support.

To generalize the difficulty: not every similarity increases the probability of the conclusion and not every difference decreases it. Some similarities and differences are known to be (or accepted as being) utterly irrelevant and should have no influence whatsoever on our probability judgments. To be viable, rule (5) would need to be supplemented with considerations of relevance , which depend upon the subject matter, historical context and logical details particular to each analogical argument. To search for a simple rule of analogical inference thus appears futile.

Carnap and his followers (Carnap 1980; Kuipers 1988; Niiniluoto 1988; Maher 2000; Romeijn 2006) have formulated principles of analogy for inductive logic, using Carnapian \(\lambda \gamma\) rules. Generally, this body of work relates to “analogy by similarity”, rather than the type of analogical reasoning discussed here. Romeijn (2006) maintains that there is a relation between Carnap’s concept of analogy and analogical prediction. His approach is a hybrid of Carnap-style inductive rules and a Bayesian model. Such an approach would need to be generalized to handle the kinds of arguments described in §2.1 . It remains unclear that the Carnapian approach can provide a general rule for analogical inference.

Norton (2010, and 2018—see Other Internet Resources) has argued that the project of formalizing inductive reasoning in terms of one or more simple formal schemata is doomed. His criticisms seem especially apt when applied to analogical reasoning. He writes:

If analogical reasoning is required to conform only to a simple formal schema, the restriction is too permissive. Inferences are authorized that clearly should not pass muster… The natural response has been to develop more elaborate formal templates… The familiar difficulty is that these embellished schema never seem to be quite embellished enough; there always seems to be some part of the analysis that must be handled intuitively without guidance from strict formal rules. (2018: 1)

Norton takes the point one step further, in keeping with his “material theory” of inductive inference. He argues that there is no universal logical principle that “powers” analogical inference “by asserting that things that share some properties must share others.” Rather, each analogical inference is warranted by some local constellation of facts about the target system that he terms “the fact of analogy”. These local facts are to be determined and investigated on a case by case basis.

To embrace a purely formal approach to analogy and to abjure formalization entirely are two extremes in a spectrum of strategies. There are intermediate positions. Most recent analyses (both philosophical and computational) have been directed towards elucidating criteria and procedures, rather than formal rules, for reasoning by analogy. So long as these are not intended to provide a universal ‘logic’ of analogy, there is room for such criteria even if one accepts Norton’s basic point. The next section discusses some of these criteria and procedures.

3. Criteria for evaluating analogical arguments

Logicians and philosophers of science have identified ‘textbook-style’ general guidelines for evaluating analogical arguments (Mill 1843/1930; Keynes 1921; Robinson 1930; Stebbing 1933; Copi and Cohen 2005; Moore and Parker 1998; Woods, Irvine, and Walton 2004). Here are some of the most important ones:

These principles can be helpful, but are frequently too vague to provide much insight. How do we count similarities and differences in applying (G1) and (G2)? Why are the structural and causal analogies mentioned in (G5) and (G6) especially important, and which structural and causal features merit attention? More generally, in connection with the all-important (G7): how do we determine which similarities and differences are relevant to the conclusion? Furthermore, what are we to say about similarities and differences that have been omitted from an analogical argument but might still be relevant?

An additional problem is that the criteria can pull in different directions. To illustrate, consider Reid’s argument for life on other planets ( Example 2 ). Stebbing (1933) finds Reid’s argument “suggestive” and “not unplausible” because the conclusion is weak (G4), while Mill (1843/1930) appears to reject the argument on account of our vast ignorance of properties that might be relevant (G3).

There is a further problem that relates to the distinction just made (in §2.3 ) between two kinds of plausibility. Each of the above criteria apart from (G7) is expressed in terms of the strength of the argument, i.e., the degree of support for the conclusion. The criteria thus appear to presuppose the probabilistic interpretation of plausibility. The problem is that a great many analogical arguments aim to establish prima facie plausibility rather than any degree of probability. Most of the guidelines are not directly applicable to such arguments.

Aristotle sets the stage for all later theories of analogical reasoning. In his theoretical reflections on analogy and in his most judicious examples, we find a sober account that lays the foundation both for the commonsense guidelines noted above and for more sophisticated analyses.

Although Aristotle employs the term analogy ( analogia ) and discusses analogical predication , he never talks about analogical reasoning or analogical arguments per se . He does, however, identify two argument forms, the argument from example ( paradeigma ) and the argument from likeness ( homoiotes ), both closely related to what would we now recognize as an analogical argument.

The argument from example ( paradeigma ) is described in the Rhetoric and the Prior Analytics :

Enthymemes based upon example are those which proceed from one or more similar cases, arrive at a general proposition, and then argue deductively to a particular inference. ( Rhetoric 1402b15) Let \(A\) be evil, \(B\) making war against neighbours, \(C\) Athenians against Thebans, \(D\) Thebans against Phocians. If then we wish to prove that to fight with the Thebans is an evil, we must assume that to fight against neighbours is an evil. Conviction of this is obtained from similar cases, e.g., that the war against the Phocians was an evil to the Thebans. Since then to fight against neighbours is an evil, and to fight against the Thebans is to fight against neighbours, it is clear that to fight against the Thebans is an evil. ( Pr. An. 69a1)

Aristotle notes two differences between this argument form and induction (69a15ff.): it “does not draw its proof from all the particular cases” (i.e., it is not a “complete” induction), and it requires an additional (deductively valid) syllogism as the final step. The argument from example thus amounts to single-case induction followed by deductive inference. It has the following structure (using \(\supset\) for the conditional):

In the terminology of §2.2, \(P\) is the positive analogy and \(Q\) is the hypothetical analogy. In Aristotle’s example, \(S\) (the source) is war between Phocians and Thebans, \(T\) (the target) is war between Athenians and Thebans, \(P\) is war between neighbours, and \(Q\) is evil. The first inference (dashed arrow) is inductive; the second and third (solid arrows) are deductively valid.

The paradeigma has an interesting feature: it is amenable to an alternative analysis as a purely deductive argument form. Let us concentrate on Aristotle’s assertion, “we must assume that to fight against neighbours is an evil,” represented as \(\forall x(P(x) \supset Q(x))\). Instead of regarding this intermediate step as something reached by induction from a single case, we might instead regard it as a hidden presupposition. This transforms the paradeigma into a syllogistic argument with a missing or enthymematic premise, and our attention shifts to possible means for establishing that premise (with single-case induction as one such means). Construed in this way, Aristotle’s paradeigma argument foreshadows deductive analyses of analogical reasoning (see §4.1 ).

The argument from likeness ( homoiotes ) seems to be closer than the paradeigma to our contemporary understanding of analogical arguments. This argument form receives considerable attention in Topics I, 17 and 18 and again in VIII, 1. The most important passage is the following.

Try to secure admissions by means of likeness; for such admissions are plausible, and the universal involved is less patent; e.g. that as knowledge and ignorance of contraries is the same, so too perception of contraries is the same; or vice versa, that since the perception is the same, so is the knowledge also. This argument resembles induction, but is not the same thing; for in induction it is the universal whose admission is secured from the particulars, whereas in arguments from likeness, what is secured is not the universal under which all the like cases fall. ( Topics 156b10–17)

This passage occurs in a work that offers advice for framing dialectical arguments when confronting a somewhat skeptical interlocutor. In such situations, it is best not to make one’s argument depend upon securing agreement about any universal proposition. The argument from likeness is thus clearly distinct from the paradeigma , where the universal proposition plays an essential role as an intermediate step in the argument. The argument from likeness, though logically less straightforward than the paradeigma , is exactly the sort of analogical reasoning we want when we are unsure about underlying generalizations.

In Topics I 17, Aristotle states that any shared attribute contributes some degree of likeness. It is natural to ask when the degree of likeness between two things is sufficiently great to warrant inferring a further likeness. In other words, when does the argument from likeness succeed? Aristotle does not answer explicitly, but a clue is provided by the way he justifies particular arguments from likeness. As Lloyd (1966) has observed, Aristotle typically justifies such arguments by articulating a (sometimes vague) causal principle which governs the two phenomena being compared. For example, Aristotle explains the saltiness of the sea, by analogy with the saltiness of sweat, as a kind of residual earthy stuff exuded in natural processes such as heating. The common principle is this:

Everything that grows and is naturally generated always leaves a residue, like that of things burnt, consisting in this sort of earth. ( Mete 358a17)

From this method of justification, we might conjecture that Aristotle believes that the important similarities are those that enter into such general causal principles.

Summarizing, Aristotle’s theory provides us with four important and influential criteria for the evaluation of analogical arguments:

• The strength of an analogy depends upon the number of similarities.
• Similarity reduces to identical properties and relations.
• Good analogies derive from underlying common causes or general laws.
• A good analogical argument need not pre-suppose acquaintance with the underlying universal (generalization).

These four principles form the core of a common-sense model for evaluating analogical arguments (which is not to say that they are correct; indeed, the first three will shortly be called into question). The first, as we have seen, appears regularly in textbook discussions of analogy. The second is largely taken for granted, with important exceptions in computational models of analogy ( §3.4 ). Versions of the third are found in most sophisticated theories. The final point, which distinguishes the argument from likeness and the argument from example, is endorsed in many discussions of analogy (e.g., Quine and Ullian 1970).

A slight generalization of Aristotle’s first principle helps to prepare the way for discussion of later developments. As that principle suggests, Aristotle, in common with just about everyone else who has written about analogical reasoning, organizes his analysis of the argument form around overall similarity. In the terminology of section 2.2, horizontal relationships drive the reasoning: the greater the overall similarity of the two domains, the stronger the analogical argument . Hume makes the same point, though stated negatively, in his Dialogues Concerning Natural Religion :

Wherever you depart, in the least, from the similarity of the cases, you diminish proportionably the evidence; and may at last bring it to a very weak analogy, which is confessedly liable to error and uncertainty. (1779/1947: 144)

Most theories of analogy agree with Aristotle and Hume on this general point. Disagreement relates to the appropriate way of measuring overall similarity. Some theories assign greatest weight to material analogy , which refers to shared, and typically observable, features. Others give prominence to formal analogy , emphasizing high-level structural correspondence. The next two sub-sections discuss representative accounts that illustrate these two approaches.

Hesse (1966) offers a sharpened version of Aristotle’s theory, specifically focused on analogical arguments in the sciences. She formulates three requirements that an analogical argument must satisfy in order to be acceptable:

• Requirement of material analogy . The horizontal relations must include similarities between observable properties.
• Causal condition . The vertical relations must be causal relations “in some acceptable scientific sense” (1966: 87).
• No-essential-difference condition . The essential properties and causal relations of the source domain must not have been shown to be part of the negative analogy.

3.3.1 Requirement of material analogy

For Hesse, an acceptable analogical argument must include “observable similarities” between domains, which she refers to as material analogy . Material analogy is contrasted with formal analogy . Two domains are formally analogous if both are “interpretations of the same formal theory” (1966: 68). Nomic isomorphism (Hempel 1965) is a special case in which the physical laws governing two systems have identical mathematical form. Heat and fluid flow exhibit nomic isomorphism. A second example is the analogy between the flow of electric current in a wire and fluid in a pipe. Ohm’s law

states that voltage difference along a wire equals current times a constant resistance. This has the same mathematical form as Poiseuille’s law (for ideal fluids):

which states that the pressure difference along a pipe equals the volumetric flow rate times a constant. Both of these systems can be represented by a common equation. While formal analogy is linked to common mathematical structure, it should not be limited to nomic isomorphism (Bartha 2010: 209). The idea of formal analogy generalizes to cases where there is a common mathematical structure between models for two systems. Bartha offers an even more liberal definition (2010: 195): “Two features are formally similar if they occupy corresponding positions in formally analogous theories. For example, pitch in the theory of sound corresponds to color in the theory of light.”

By contrast, material analogy consists of what Hesse calls “observable” or “pre-theoretic” similarities. These are horizontal relationships of similarity between properties of objects in the source and the target. Similarities between echoes (sound) and reflection (light), for instance, were recognized long before we had any detailed theories about these phenomena. Hesse (1966, 1988) regards such similarities as metaphorical relationships between the two domains and labels them “pre-theoretic” because they draw on personal and cultural experience. We have both material and formal analogies between sound and light, and it is significant for Hesse that the former are independent of the latter.

There are good reasons not to accept Hesse’s requirement of material analogy, construed in this narrow way. First, it is apparent that formal analogies are the starting point in many important inferences. That is certainly the case in mathematics, a field in which material analogy, in Hesse’s sense, plays no role at all. Analogical arguments based on formal analogy have also been extremely influential in physics (Steiner 1989, 1998).

In Norton’s broad sense, however, ‘material analogy’ simply refers to similarities rooted in factual knowledge of the source and target domains. With reference to this broader meaning, Hesse proposes two additional material criteria.

3.3.2 Causal condition

Hesse requires that the hypothetical analogy, the feature transferred to the target domain, be causally related to the positive analogy. In her words, the essential requirement for a good argument from analogy is “a tendency to co-occurrence”, i.e., a causal relationship. She states the requirement as follows:

The vertical relations in the model [source] are causal relations in some acceptable scientific sense, where there are no compelling a priori reasons for denying that causal relations of the same kind may hold between terms of the explanandum [target]. (1966: 87)

The causal condition rules out analogical arguments where there is no causal knowledge of the source domain. It derives support from the observation that many analogies do appear to involve a transfer of causal knowledge.

The causal condition is on the right track, but is arguably too restrictive. For example, it rules out analogical arguments in mathematics. Even if we limit attention to the empirical sciences, persuasive analogical arguments may be founded upon strong statistical correlation in the absence of any known causal connection. Consider ( Example 11 ) Benjamin Franklin’s prediction, in 1749, that pointed metal rods would attract lightning, by analogy with the way they attracted the “electrical fluid” in the laboratory:

Electrical fluid agrees with lightning in these particulars: 1. Giving light. 2. Colour of the light. 3. Crooked direction. 4. Swift motion. 5. Being conducted by metals. 6. Crack or noise in exploding. 7. Subsisting in water or ice. 8. Rending bodies it passes through. 9. Destroying animals. 10. Melting metals. 11. Firing inflammable substances. 12. Sulphureous smell.—The electrical fluid is attracted by points.—We do not know whether this property is in lightning.—But since they agree in all the particulars wherein we can already compare them, is it not probable they agree likewise in this? Let the experiment be made. ( Benjamin Franklin’s Experiments , 334)

Franklin’s hypothesis was based on a long list of properties common to the target (lightning) and source (electrical fluid in the laboratory). There was no known causal connection between the twelve “particulars” and the thirteenth property, but there was a strong correlation. Analogical arguments may be plausible even where there are no known causal relations.

3.3.3 No-essential-difference condition

Hesse’s final requirement is that the “essential properties and causal relations of the [source] have not been shown to be part of the negative analogy” (1966: 91). Hesse does not provide a definition of “essential,” but suggests that a property or relation is essential if it is “causally closely related to the known positive analogy.” For instance, an analogy with fluid flow was extremely influential in developing the theory of heat conduction. Once it was discovered that heat was not conserved, however, the analogy became unacceptable (according to Hesse) because conservation was so central to the theory of fluid flow.

This requirement, though once again on the right track, seems too restrictive. It can lead to the rejection of a good analogical argument. Consider the analogy between a two-dimensional rectangle and a three-dimensional box ( Example 7 ). Broadening Hesse’s notion, it seems that there are many ‘essential’ differences between rectangles and boxes. This does not mean that we should reject every analogy between rectangles and boxes out of hand. The problem derives from the fact that Hesse’s condition is applied to the analogy relation independently of the use to which that relation is put. What counts as essential should vary with the analogical argument. Absent an inferential context, it is impossible to evaluate the importance or ‘essentiality’ of similarities and differences.

Despite these weaknesses, Hesse’s ‘material’ criteria constitute a significant advance in our understanding of analogical reasoning. The causal condition and the no-essential-difference condition incorporate local factors, as urged by Norton, into the assessment of analogical arguments. These conditions, singly or taken together, imply that an analogical argument can fail to generate any support for its conclusion, even when there is a non-empty positive analogy. Hesse offers no theory about the ‘degree’ of analogical support. That makes her account one of the few that is oriented towards the modal, rather than probabilistic, use of analogical arguments ( §2.3 ).

Many people take the concept of model-theoretic isomorphism to set the standard for thinking about similarity and its role in analogical reasoning. They propose formal criteria for evaluating analogies, based on overall structural or syntactical similarity. Let us refer to theories oriented around such criteria as structuralist .

A number of leading computational models of analogy are structuralist. They are implemented in computer programs that begin with (or sometimes build) representations of the source and target domains, and then construct possible analogy mappings. Analogical inferences emerge as a consequence of identifying the ‘best mapping.’ In terms of criteria for analogical reasoning, there are two main ideas. First, the goodness of an analogical argument is based on the goodness of the associated analogy mapping . Second, the goodness of the analogy mapping is given by a metric that indicates how closely it approximates isomorphism.

The most influential structuralist theory has been Gentner’s structure-mapping theory, implemented in a program called the structure-mapping engine (SME). In its original form (Gentner 1983), the theory assesses analogies on purely structural grounds. Gentner asserts:

Analogies are about relations, rather than simple features. No matter what kind of knowledge (causal models, plans, stories, etc.), it is the structural properties (i.e., the interrelationships between the facts) that determine the content of an analogy. (Falkenhainer, Forbus, and Gentner 1989/90: 3)

In order to clarify this thesis, Gentner introduces a distinction between properties , or monadic predicates, and relations , which have multiple arguments. She further distinguishes among different orders of relations and functions, defined inductively (in terms of the order of the relata or arguments). The best mapping is determined by systematicity : the extent to which it places higher-order relations, and items that are nested in higher-order relations, in correspondence. Gentner’s Systematicity Principle states:

A predicate that belongs to a mappable system of mutually interconnecting relationships is more likely to be imported into the target than is an isolated predicate. (1983: 163)

A systematic analogy (one that places high-order relations and their components in correspondence) is better than a less systematic analogy. Hence, an analogical inference has a degree of plausibility that increases monotonically with the degree of systematicity of the associated analogy mapping. Gentner’s fundamental criterion for evaluating candidate analogies (and analogical inferences) thus depends solely upon the syntax of the given representations and not at all upon their content.

Later versions of the structure-mapping theory incorporate refinements (Forbus, Ferguson, and Gentner 1994; Forbus 2001; Forbus et al. 2007; Forbus et al. 2008; Forbus et al 2017). For example, the earliest version of the theory is vulnerable to worries about hand-coded representations of source and target domains. Gentner and her colleagues have attempted to solve this problem in later work that generates LISP representations from natural language text (see Turney 2008 for a different approach).

The most important challenges for the structure-mapping approach relate to the Systematicity Principle itself. Does the value of an analogy derive entirely, or even chiefly, from systematicity? There appear to be two main difficulties with this view. First: it is not always appropriate to give priority to systematic, high-level relational matches. Material criteria, and notably what Gentner refers to as “superficial feature matches,” can be extremely important in some types of analogical reasoning, such as ethnographic analogies which are based, to a considerable degree, on surface resemblances between artifacts. Second and more significantly: systematicity seems to be at best a fallible marker for good analogies rather than the essence of good analogical reasoning.

Greater systematicity is neither necessary nor sufficient for a more plausible analogical inference. It is obvious that increased systematicity is not sufficient for increased plausibility. An implausible analogy can be represented in a form that exhibits a high degree of structural parallelism. High-order relations can come cheap, as we saw with Achinstein’s “swan” example ( §2.4 ).

More pointedly, increased systematicity is not necessary for greater plausibility. Indeed, in causal analogies, it may even weaken the inference. That is because systematicity takes no account of the type of causal relevance, positive or negative. (McKay 1993) notes that microbes have been found in frozen lakes in Antarctica; by analogy, simple life forms might exist on Mars. Freezing temperatures are preventive or counteracting causes; they are negatively relevant to the existence of life. The climate of Mars was probably more favorable to life 3.5 billion years ago than it is today, because temperatures were warmer. Yet the analogy between Antarctica and present-day Mars is more systematic than the analogy between Antarctica and ancient Mars. According to the Systematicity Principle , the analogy with Antarctica provides stronger support for life on Mars today than it does for life on ancient Mars.

The point of this example is that increased systematicity does not always increase plausibility, and reduced systematicity does not always decrease it (see Lee and Holyoak 2008). The more general point is that systematicity can be misleading, unless we take into account the nature of the relationships between various factors and the hypothetical analogy. Systematicity does not magically produce or explain the plausibility of an analogical argument. When we reason by analogy, we must determine which features of both domains are relevant and how they relate to the analogical conclusion. There is no short-cut via syntax.

Schlimm (2008) offers an entirely different critique of the structure-mapping theory from the perspective of analogical reasoning in mathematics—a domain where one might expect a formal approach such as structure mapping to perform well. Schlimm introduces a simple distinction: a domain is object-rich if the number of objects is greater than the number of relations (and properties), and relation-rich otherwise. Proponents of the structure-mapping theory typically focus on relation-rich examples (such as the analogy between the solar system and the atom). By contrast, analogies in mathematics typically involve domains with an enormous number of objects (like the real numbers), but relatively few relations and functions (addition, multiplication, less-than).

Schlimm provides an example of an analogical reasoning problem in group theory that involves a single relation in each domain. In this case, attaining maximal systematicity is trivial. The difficulty is that, compatible with maximal systematicity, there are different ways in which the objects might be placed in correspondence. The structure-mapping theory appears to yield the wrong inference. We might put the general point as follows: in object-rich domains, systematicity ceases to be a reliable guide to plausible analogical inference.

3.5.1 Connectionist models

During the past thirty-five years, cognitive scientists have conducted extensive research on analogy. Gentner’s SME is just one of many computational theories, implemented in programs that construct and use analogies. Three helpful anthologies that span this period are Helman 1988; Gentner, Holyoak, and Kokinov 2001; and Kokinov, Holyoak, and Gentner 2009.

One predominant objective of this research has been to model the cognitive processes involved in using analogies. Early models tended to be oriented towards “understanding the basic constraints that govern human analogical thinking” (Hummel and Holyoak 1997: 458). Recent connectionist models have been directed towards uncovering the psychological mechanisms that come into play when we use analogies: retrieval of a relevant source domain, analogical mapping across domains, and transfer of information and learning of new categories or schemas.

In some cases, such as the structure-mapping theory (§3.4), this research overlaps directly with the normative questions that are the focus of this entry; indeed, Gentner’s Systematicity Principle may be interpreted normatively. In other cases, we might view the projects as displacing those traditional normative questions with up-to-date, computational forms of naturalized epistemology . Two approaches are singled out here because both raise important challenges to the very idea of finding sharp answers to those questions, and both suggest that connectionist models offer a more fruitful approach to understanding analogical reasoning.

The first is the constraint-satisfaction model (also known as the multiconstraint theory ), developed by Holyoak and Thagard (1989, 1995). Like Gentner, Holyoak and Thagard regard the heart of analogical reasoning as analogy mapping , and they stress the importance of systematicity, which they refer to as a structural constraint. Unlike Gentner, they acknowledge two additional types of constraints. Pragmatic constraints take into account the goals and purposes of the agent, recognizing that “the purpose will guide selection” of relevant similarities. Semantic constraints represent estimates of the degree to which people regard source and target items as being alike, rather like Hesse’s “pre-theoretic” similarities.

The novelty of the multiconstraint theory is that these structural , semantic and pragmatic constraints are implemented not as rigid rules, but rather as ‘pressures’ supporting or inhibiting potential pairwise correspondences. The theory is implemented in a connectionist program called ACME (Analogical Constraint Mapping Engine), which assigns an initial activation value to each possible pairing between elements in the source and target domains (based on semantic and pragmatic constraints), and then runs through cycles that update the activation values based on overall coherence (structural constraints). The best global analogy mapping emerges under the pressure of these constraints. Subsequent connectionist models, such as Hummel and Holyoak’s LISA program (1997, 2003), have made significant advances and hold promise for offering a more complete theory of analogical reasoning.

The second example is Hofstadter and Mitchell’s Copycat program (Hofstadter 1995; Mitchell 1993). The program is “designed to discover insightful analogies, and to do so in a psychologically realistic way” (Hofstadter 1995: 205). Copycat operates in the domain of letter-strings. The program handles the following type of problem:

Suppose the letter-string abc were changed to abd ; how would you change the letter-string ijk in “the same way”?

Most people would answer ijl , since it is natural to think that abc was changed to abd by the “transformation rule”: replace the rightmost letter with its successor. Alternative answers are possible, but do not agree with most people’s sense of what counts as the natural analogy.

Hofstadter and Mitchell believe that analogy-making is in large part about the perception of novel patterns, and that such perception requires concepts with “fluid” boundaries. Genuine analogy-making involves “slippage” of concepts. The Copycat program combines a set of core concepts pertaining to letter-sequences ( successor , leftmost and so forth) with probabilistic “halos” that link distinct concepts dynamically. Orderly structures emerge out of random low-level processes and the program produces plausible solutions. Copycat thus shows that analogy-making can be modeled as a process akin to perception, even if the program employs mechanisms distinct from those in human perception.

The multiconstraint theory and Copycat share the idea that analogical cognition involves cognitive processes that operate below the level of abstract reasoning. Both computational models—to the extent that they are capable of performing successful analogical reasoning—challenge the idea that a successful model of analogical reasoning must take the form of a set of quasi-logical criteria. Efforts to develop a quasi-logical theory of analogical reasoning, it might be argued, have failed. In place of faulty inference schemes such as those described earlier ( §2.2 , §2.4 ), computational models substitute procedures that can be judged on their performance rather than on traditional philosophical standards.

In response to this argument, we should recognize the value of the connectionist models while acknowledging that we still need a theory that offers normative principles for evaluating analogical arguments. In the first place, even if the construction and recognition of analogies are largely a matter of perception, this does not eliminate the need for subsequent critical evaluation of analogical inferences. Second and more importantly, we need to look not just at the construction of analogy mappings but at the ways in which individual analogical arguments are debated in fields such as mathematics, physics, philosophy and the law. These high-level debates require reasoning that bears little resemblance to the computational processes of ACME or Copycat. (Ashley’s HYPO (Ashley 1990) is one example of a non-connectionist program that focuses on this aspect of analogical reasoning.) There is, accordingly, room for both computational and traditional philosophical models of analogical reasoning.

3.5.2 Articulation model

Most prominent theories of analogy, philosophical and computational, are based on overall similarity between source and target domains—defined in terms of some favoured subset of Hesse’s horizontal relations (see §2.2 ). Aristotle and Mill, whose approach is echoed in textbook discussions, suggest counting similarities. Hesse’s theory ( §3.3 ) favours “pre-theoretic” correspondences. The structure-mapping theory and its successors ( §3.4 ) look to systematicity, i.e., to correspondences involving complex, high-level networks of relations. In each of these approaches, the problem is twofold: overall similarity is not a reliable guide to plausibility, and it fails to explain the plausibility of any analogical argument.

Bartha’s articulation model (2010) proposes a different approach, beginning not with horizontal relations, but rather with a classification of analogical arguments on the basis of the vertical relations within each domain. The fundamental idea is that a good analogical argument must satisfy two conditions:

Prior Association . There must be a clear connection, in the source domain, between the known similarities (the positive analogy) and the further similarity that is projected to hold in the target domain (the hypothetical analogy). This relationship determines which features of the source are critical to the analogical inference.

Potential for Generalization . There must be reason to think that the same kind of connection could obtain in the target domain. More pointedly: there must be no critical disanalogy between the domains.

The first order of business is to make the prior association explicit. The standards of explicitness vary depending on the nature of this association (causal relation, mathematical proof, functional relationship, and so forth). The two general principles are fleshed out via a set of subordinate models that allow us to identify critical features and hence critical disanalogies.

To see how this works, consider Example 7 (Rectangles and boxes). In this analogical argument, the source domain is two-dimensional geometry: we know that of all rectangles with a fixed perimeter, the square has maximum area. The target domain is three-dimensional geometry: by analogy, we conjecture that of all boxes with a fixed surface area, the cube has maximum volume. This argument should be evaluated not by counting similarities, looking to pre-theoretic resemblances between rectangles and boxes, or constructing connectionist representations of the domains and computing a systematicity score for possible mappings. Instead, we should begin with a precise articulation of the prior association in the source domain, which amounts to a specific proof for the result about rectangles. We should then identify, relative to that proof, the critical features of the source domain: namely, the concepts and assumptions used in the proof. Finally, we should assess the potential for generalization: whether, in the three-dimensional setting, those critical features are known to lack analogues in the target domain. The articulation model is meant to reflect the conversations that can and do take place between an advocate and a critic of an analogical argument.

3.6.1 Norton’s material theory of analogy

As noted in §2.4 , Norton rejects analogical inference rules. But even if we agree with Norton on this point, we might still be interested in having an account that gives us guidelines for evaluating analogical arguments. How does Norton’s approach fare on this score?

According to Norton, each analogical argument is warranted by local facts that must be investigated and justified empirically. First, there is “the fact of the analogy”: in practice, a low-level uniformity that embraces both the source and target systems. Second, there are additional factual properties of the target system which, when taken together with the uniformity, warrant the analogical inference. Consider Galileo’s famous inference ( Example 12 ) that there are mountains on the moon (Galileo 1610). Through his newly invented telescope, Galileo observed points of light on the moon ahead of the advancing edge of sunlight. Noting that the same thing happens on earth when sunlight strikes the mountains, he concluded that there must be mountains on the moon and even provided a reasonable estimate of their height. In this example, Norton tells us, the the fact of the analogy is that shadows and other optical phenomena are generated in the same way on the earth and on the moon; the additional fact about the target is the existence of points of light ahead of the advancing edge of sunlight on the moon.

What are the implications of Norton’s material theory when it comes to evaluating analogical arguments? The fact of the analogy is a local uniformity that powers the inference. Norton’s theory works well when such a uniformity is patent or naturally inferred. It doesn’t work well when the uniformity is itself the target (rather than the driver ) of the inference. That happens with explanatory analogies such as Example 5 (the Acoustical Analogy ), and mathematical analogies such as Example 7 ( Rectangles and Boxes ). Similarly, the theory doesn’t work well when the underlying uniformity is unclear, as in Example 2 ( Life on other Planets ), Example 4 ( Clay Pots ), and many other cases. In short, if Norton’s theory is accepted, then for most analogical arguments there are no useful evaluation criteria.

3.6.2 Field-specific criteria

For those who sympathize with Norton’s skepticism about universal inductive schemes and theories of analogical reasoning, yet recognize that his approach may be too local, an appealing strategy is to move up one level. We can aim for field-specific “working logics” (Toulmin 1958; Wylie and Chapman 2016; Reiss 2015). This approach has been adopted by philosophers of archaeology, evolutionary biology and other historical sciences (Wylie and Chapman 2016; Currie 2013; Currie 2016; Currie 2018). In place of schemas, we find ‘toolkits’, i.e., lists of criteria for evaluating analogical reasoning.

For example, Currie (2016) explores in detail the use of ethnographic analogy ( Example 13 ) between shamanistic motifs used by the contemporary San people and similar motifs in ancient rock art, found both among ancestors of the San (direct historical analogy) and in European rock art (indirect historical analogy). Analogical arguments support the hypothesis that in each of these cultures, rock art symbolizes hallucinogenic experiences. Currie examines criteria that focus on assumptions about stability of cultural traits and environment-culture relationships. Currie (2016, 2018) and Wylie (Wylie and Chapman 2016) also stress the importance of robustness reasoning that combines analogical arguments of moderate strength with other forms of evidence to yield strong conclusions.

Practice-based approaches can thus yield specific guidelines unlikely to be matched by any general theory of analogical reasoning. One caveat is worth mentioning. Field-specific criteria for ethnographic analogy are elicited against a background of decades of methodological controversy (Wylie and Chapman 2016). Critics and defenders of ethnographic analogy have appealed to general models of scientific method (e.g., hypothetico-deductive method or Bayesian confirmation). To advance the methodological debate, practice-based approaches must either make connections to these general models or explain why the lack of any such connection is unproblematic.

3.6.3 Formal analogies in physics

Close attention to analogical arguments in practice can also provide valuable challenges to general ideas about analogical inference. In an interesting discussion, Steiner (1989, 1998) suggests that many of the analogies that played a major role in early twentieth-century physics count as “Pythagorean.” The term is meant to connote mathematical mysticism: a “Pythagorean” analogy is a purely formal analogy, one founded on mathematical similarities that have no known physical basis at the time it is proposed. One example is Schrödinger’s use of analogy ( Example 14 ) to “guess” the form of the relativistic wave equation. In Steiner’s view, Schrödinger’s reasoning relies upon manipulations and substitutions based on purely mathematical analogies. Steiner argues that the success, and even the plausibility, of such analogies “evokes, or should evoke, puzzlement” (1989: 454). Both Hesse (1966) and Bartha (2010) reject the idea that a purely formal analogy, with no physical significance, can support a plausible analogical inference in physics. Thus, Steiner’s arguments provide a serious challenge.

Bartha (2010) suggests a response: we can decompose Steiner’s examples into two or more steps, and then establish that at least one step does, in fact, have a physical basis. Fraser (forthcoming), however, offers a counterexample that supports Steiner’s position. Complex analogies between classical statistical mechanics (CSM) and quantum field theory (QFT) have played a crucial role in the development and application of renormalization group (RG) methods in both theories ( Example 15 ). Fraser notes substantial physical disanalogies between CSM and QFT, and concludes that the reasoning is based entirely on formal analogies.

4. Philosophical foundations for analogical reasoning

What philosophical basis can be provided for reasoning by analogy? What justification can be given for the claim that analogical arguments deliver plausible conclusions? There have been several ideas for answering this question. One natural strategy assimilates analogical reasoning to some other well-understood argument pattern, a form of deductive or inductive reasoning ( §4.1 , §4.2 ). A few philosophers have explored the possibility of a priori justification ( §4.3 ). A pragmatic justification may be available for practical applications of analogy, notably in legal reasoning ( §4.4 ).

Any attempt to provide a general justification for analogical reasoning faces a basic dilemma. The demands of generality require a high-level formulation of the problem and hence an abstract characterization of analogical arguments, such as schema (4). On the other hand, as noted previously, many analogical arguments that conform to schema (4) are bad arguments. So a general justification of analogical reasoning cannot provide support for all arguments that conform to (4), on pain of proving too much. Instead, it must first specify a subset of putatively ‘good’ analogical arguments, and link the general justification to this specified subset. The problem of justification is linked to the problem of characterizing good analogical arguments . This difficulty afflicts some of the strategies described in this section.

Analogical reasoning may be cast in a deductive mold. If successful, this strategy neatly solves the problem of justification. A valid deductive argument is as good as it gets.

An early version of the deductivist approach is exemplified by Aristotle’s treatment of the argument from example ( §3.2 ), the paradeigma . On this analysis, an analogical argument between source domain \(S\) and target \(T\) begins with the assumption of positive analogy \(P(S)\) and \(P(T)\), as well as the additional information \(Q(S)\). It proceeds via the generalization \(\forall x(P(x) \supset Q(x))\) to the conclusion: \(Q(T)\). Provided we can treat that intermediate generalization as an independent premise, we have a deductively valid argument. Notice, though, that the existence of the generalization renders the analogy irrelevant. We can derive \(Q(T)\) from the generalization and \(P(T)\), without any knowledge of the source domain. The literature on analogy in argumentation theory ( §2.2 ) offers further perspectives on this type of analysis, and on the question of whether analogical arguments are properly characterized as deductive.

Some recent analyses follow Aristotle in treating analogical arguments as reliant upon extra (sometimes tacit) premises, typically drawn from background knowledge, that convert the inference into a deductively valid argument––but without making the source domain irrelevant. Davies and Russell introduce a version that relies upon what they call determination rules (Russell 1986; Davies and Russell 1987; Davies 1988). Suppose that \(Q\) and \(P_1 , \ldots ,P_m\) are variables, and we have background knowledge that the value of \(Q\) is determined by the values of \(P_1 , \ldots ,P_m\). In the simplest case, where \(m = 1\) and both \(P\) and \(Q\) are binary Boolean variables, this reduces to

i.e., whether or not \(P\) holds determines whether or not \(Q\) holds. More generally, the form of a determination rule is

i.e., \(Q\) is a function of \(P_1,\ldots\), \(P_m\). If we assume such a rule as part of our background knowledge, then an analogical argument with conclusion \(Q(T)\) is deductively valid. More precisely, and allowing for the case where \(Q\) is not a binary variable: if we have such a rule, and also premises stating that the source \(S\) agrees with the target \(T\) on all of the values \(P_i\), then we may validly infer that \(Q(T) = Q(S)\).

The “determination rule” analysis provides a clear and simple justification for analogical reasoning. Note that, in contrast to the Aristotelian analysis via the generalization \(\forall x(P(x) \supset Q(x))\), a determination rule does not trivialize the analogical argument. Only by combining the rule with information about the source domain can we derive the value of \(Q(T)\). To illustrate by adapting one of the examples given by Russell and Davies ( Example 16 ), let’s suppose that the value \((Q)\) of a used car (relative to a particular buyer) is determined by its year, make, mileage, condition, color and accident history (the variables \(P_i)\). It doesn’t matter if one or more of these factors are redundant or irrelevant. Provided two cars are indistinguishable on each of these points, they will have the same value. Knowledge of the source domain is necessary; we can’t derive the value of the second car from the determination rule alone. Weitzenfeld (1984) proposes a variant of this approach, advancing the slightly more general thesis that analogical arguments are deductive arguments with a missing (enthymematic) premise that amounts to a determination rule.

Do determination rules give us a solution to the problem of providing a justification for analogical arguments? In general: no. Analogies are commonly applied to problems such as Example 8 ( morphine and meperidine ), where we are not even aware of all relevant factors, let alone in possession of a determination rule. Medical researchers conduct drug tests on animals without knowing all attributes that might be relevant to the effects of the drug. Indeed, one of the main objectives of such testing is to guard against reactions unanticipated by theory. On the “determination rule” analysis, we must either limit the scope of such arguments to cases where we have a well-supported determination rule, or focus attention on formulating and justifying an appropriate determination rule. For cases such as animal testing, neither option seems realistic.

Recasting analogy as a deductive argument may help to bring out background assumptions, but it makes little headway with the problem of justification. That problem re-appears as the need to state and establish the plausibility of a determination rule, and that is at least as difficult as justifying the original analogical argument.

Some philosophers have attempted to portray, and justify, analogical reasoning in terms of some well-understood inductive argument pattern. There have been three moderately popular versions of this strategy. The first treats analogical reasoning as generalization from a single case. The second treats it as a kind of sampling argument. The third recognizes the argument from analogy as a distinctive form, but treats past successes as evidence for future success.

4.2.1 Single-case induction

Let’s reconsider Aristotle’s argument from example or paradeigma ( §3.2 ), but this time regard the generalization as justified via induction from a single case (the source domain). Can such a simple analysis of analogical arguments succeed? In general: no.

A single instance can sometimes lead to a justified generalization. Cartwright (1992) argues that we can sometimes generalize from a single careful experiment, “where we have sufficient control of the materials and our knowledge of the requisite background assumptions is secure” (51). Cartwright thinks that we can do this, for example, in experiments with compounds that have stable “Aristotelian natures.” In a similar spirit, Quine (1969) maintains that we can have instantial confirmation when dealing with natural kinds.

Even if we accept that there are such cases, the objection to understanding all analogical arguments as single-case induction is obvious: the view is simply too restrictive. Most analogical arguments will not meet the requisite conditions. We may not know that we are dealing with a natural kind or Aristotelian nature when we make the analogical argument. We may not know which properties are essential. An insistence on the ‘single-case induction’ analysis of analogical reasoning is likely to lead to skepticism (Agassi 1964, 1988).

Interpreting the argument from analogy as single-case induction is also counter-productive in another way. The simplistic analysis does nothing to advance the search for criteria that help us to distinguish between relevant and irrelevant similarities, and hence between good and bad analogical arguments.

4.2.2 Sampling arguments

On the sampling conception of analogical arguments, acknowledged similarities between two domains are treated as statistically relevant evidence for further similarities. The simplest version of the sampling argument is due to Mill (1843/1930). An argument from analogy, he writes, is “a competition between the known points of agreement and the known points of difference.” Agreement of \(A\) and \(B\) in 9 out of 10 properties implies a probability of 0.9 that \(B\) will possess any other property of \(A\): “we can reasonably expect resemblance in the same proportion” (367). His only restriction has to do with sample size: we must be relatively knowledgeable about both \(A\) and \(B\). Mill saw no difficulty in using analogical reasoning to infer characteristics of newly discovered species of plants or animals, given our extensive knowledge of botany and zoology. But if the extent of unascertained properties of \(A\) and \(B\) is large, similarity in a small sample would not be a reliable guide; hence, Mill’s dismissal of Reid’s argument about life on other planets ( Example 2 ).

The sampling argument is presented in more explicit mathematical form by Harrod (1956). The key idea is that the known properties of \(S\) (the source domain) may be considered a random sample of all \(S\)’s properties—random, that is, with respect to the attribute of also belonging to \(T\) (the target domain). If the majority of known properties that belong to \(S\) also belong to \(T\), then we should expect most other properties of \(S\) to belong to \(T\), for it is unlikely that we would have come to know just the common properties. In effect, Harrod proposes a binomial distribution, modeling ‘random selection’ of properties on random selection of balls from an urn.

There are grave difficulties with Harrod’s and Mill’s analyses. One obvious difficulty is the counting problem : the ‘population’ of properties is poorly defined. How are we to count similarities and differences? The ratio of shared to total known properties varies dramatically according to how we do this. A second serious difficulty is the problem of bias : we cannot justify the assumption that the sample of known features is random. In the case of the urn, the selection process is arranged so that the result of each choice is not influenced by the agent’s intentions or purposes, or by prior choices. By contrast, the presentation of an analogical argument is always partisan. Bias enters into the initial representation of similarities and differences: an advocate of the argument will highlight similarities, while a critic will play up differences. The paradigm of repeated selection from an urn seems totally inappropriate. Additional variations of the sampling approach have been developed (e.g., Russell 1988), but ultimately these versions also fail to solve either the counting problem or the problem of bias.

4.2.3 Argument from past success

Section 3.6 discussed Steiner’s view that appeal to ‘Pythagorean’ analogies in physics “evokes, or should evoke, puzzlement” (1989: 454). Liston (2000) offers a possible response: physicists are entitled to use Pythagorean analogies on the basis of induction from their past success:

[The scientist] can admit that no one knows how [Pythagorean] reasoning works and argue that the very fact that similar strategies have worked well in the past is already reason enough to continue pursuing them hoping for success in the present instance. (200)

Setting aside familiar worries about arguments from success, the real problem here is to determine what counts as a similar strategy. In essence, that amounts to isolating the features of successful Pythagorean analogies. As we have seen (§2.4), nobody has yet provided a satisfactory scheme that characterizes successful analogical arguments, let alone successful Pythagorean analogical arguments.

An a priori approach traces the validity of a pattern of analogical reasoning, or of a particular analogical argument, to some broad and fundamental principle. Three such approaches will be outlined here.

The first is due to Keynes (1921). Keynes appeals to his famous Principle of the Limitation of Independent Variety, which he articulates as follows:

Armed with this Principle and some additional assumptions, Keynes is able to show that in cases where there is no negative analogy , knowledge of the positive analogy increases the (logical) probability of the conclusion. If there is a non-trivial negative analogy, however, then the probability of the conclusion remains unchanged, as was pointed out by Hesse (1966). Those familiar with Carnap’s theory of logical probability will recognize that in setting up his framework, Keynes settled on a measure that permits no learning from experience.

Hesse offers a refinement of Keynes’s strategy, once again along Carnapian lines. In her (1974), she proposes what she calls the Clustering Postulate : the assumption that our epistemic probability function has a built-in bias towards generalization. The objections to such postulates of uniformity are well-known (see Salmon 1967), but even if we waive them, her argument fails. The main objection here—which also applies to Keynes—is that a purely syntactic axiom such as the Clustering Postulate fails to discriminate between analogical arguments that are good and those that are clearly without value (according to Hesse’s own material criteria, for example).

A different a priori strategy, proposed by Bartha (2010), limits the scope of justification to analogical arguments that satisfy tentative criteria for ‘good’ analogical reasoning. The criteria are those specified by the articulation model ( §3.5 ). In simplified form, they require the existence of non-trivial positive analogy and no known critical disanalogy. The scope of Bartha’s argument is also limited to analogical arguments directed at establishing prima facie plausibility, rather than degree of probability.

Bartha’s argument rests on a principle of symmetry reasoning articulated by van Fraassen (1989: 236): “problems which are essentially the same must receive essentially the same solution.” A modal extension of this principle runs roughly as follows: if problems might be essentially the same, then they might have essentially the same solution. There are two modalities here. Bartha argues that satisfaction of the criteria of the articulation model is sufficient to establish the modality in the antecedent, i.e., that the source and target domains ‘might be essentially the same’ in relevant respects. He further suggests that prima facie plausibility provides a reasonable reading of the modality in the consequent, i.e., that the problems in the two domains ‘might have essentially the same solution.’ To call a hypothesis prima facie plausible is to elevate it to the point where it merits investigation, since it might be correct.

The argument is vulnerable to two sorts of concerns. First, there are questions about the interpretation of the symmetry principle. Second, there is a residual worry that this justification, like all the others, proves too much. The articulation model may be too vague or too permissive.

Arguably, the most promising available defense of analogical reasoning may be found in its application to case law (see Precedent and Analogy in Legal Reasoning ). Judicial decisions are based on the verdicts and reasoning that have governed relevantly similar cases, according to the doctrine of stare decisis (Levi 1949; Llewellyn 1960; Cross and Harris 1991; Sunstein 1993). Individual decisions by a court are binding on that court and lower courts; judges are obligated to decide future cases ‘in the same way.’ That is, the reasoning applied in an individual decision, referred to as the ratio decidendi , must be applied to similar future cases (see Example 10 ). In practice, of course, the situation is extremely complex. No two cases are identical. The ratio must be understood in the context of the facts of the original case, and there is considerable room for debate about its generality and its applicability to future cases. If a consensus emerges that a past case was wrongly decided, later judgments will distinguish it from new cases, effectively restricting the scope of the ratio to the original case.

The practice of following precedent can be justified by two main practical considerations. First, and above all, the practice is conservative : it provides a relatively stable basis for replicable decisions. People need to be able to predict the actions of the courts and formulate plans accordingly. Stare decisis serves as a check against arbitrary judicial decisions. Second, the practice is still reasonably progressive : it allows for the gradual evolution of the law. Careful judges distinguish bad decisions; new values and a new consensus can emerge in a series of decisions over time.

In theory, then, stare decisis strikes a healthy balance between conservative and progressive social values. This justification is pragmatic. It pre-supposes a common set of social values, and links the use of analogical reasoning to optimal promotion of those values. Notice also that justification occurs at the level of the practice in general; individual analogical arguments sometimes go astray. A full examination of the nature and foundations for stare decisis is beyond the scope of this entry, but it is worth asking the question: might it be possible to generalize the justification for stare decisis ? Is a parallel pragmatic justification available for analogical arguments in general?

Bartha (2010) offers a preliminary attempt to provide such a justification by shifting from social values to epistemic values. The general idea is that reasoning by analogy is especially well suited to the attainment of a common set of epistemic goals or values. In simple terms, analogical reasoning—when it conforms to certain criteria—achieves an excellent (perhaps optimal) balance between the competing demands of stability and innovation. It supports both conservative epistemic values, such as simplicity and coherence with existing belief, and progressive epistemic values, such as fruitfulness and theoretical unification (McMullin (1993) provides a classic list).

5. Beyond analogical arguments

As emphasized earlier, analogical reasoning takes in a great deal more than analogical arguments. In this section, we examine two broad contexts in which analogical reasoning is important.

The first, still closely linked to analogical arguments, is the confirmation of scientific hypotheses. Confirmation is the process by which a scientific hypothesis receives inductive support on the basis of evidence (see evidence , confirmation , and Bayes’ Theorem ). Confirmation may also signify the logical relationship of inductive support that obtains between a hypothesis \(H\) and a proposition \(E\) that expresses the relevant evidence. Can analogical arguments play a role, either in the process or in the logical relationship? Arguably yes (to both), but this role has to be delineated carefully, and several obstacles remain in the way of a clear account.

The second context is conceptual and theoretical development in cutting-edge scientific research. Analogies are used to suggest possible extensions of theoretical concepts and ideas. The reasoning is linked to considerations of plausibility, but there is no straightforward analysis in terms of analogical arguments.

How is analogical reasoning related to the confirmation of scientific hypotheses? The examples and philosophical discussion from earlier sections suggest that a good analogical argument can indeed provide support for a hypothesis. But there are good reasons to doubt the claim that analogies provide actual confirmation.

In the first place, there is a logical difficulty. To appreciate this, let us concentrate on confirmation as a relationship between propositions. Christensen (1999: 441) offers a helpful general characterization:

Some propositions seem to help make it rational to believe other propositions. When our current confidence in \(E\) helps make rational our current confidence in \(H\), we say that \(E\) confirms \(H\).

In the Bayesian model, ‘confidence’ is represented in terms of subjective probability. A Bayesian agent starts with an assignment of subjective probabilities to a class of propositions. Confirmation is understood as a three-place relation:

\(E\) represents a proposition about accepted evidence, \(H\) stands for a hypothesis, \(K\) for background knowledge and \(Pr\) for the agent’s subjective probability function. To confirm \(H\) is to raise its conditional probability, relative to \(K\). The shift from prior probability \(Pr(H \mid K)\) to posterior probability \(Pr(H \mid E \cdot K)\) is referred to as conditionalization on \(E\). The relation between these two probabilities is typically given by Bayes’ Theorem (setting aside more complex forms of conditionalization):

For Bayesians, here is the logical difficulty: it seems that an analogical argument cannot provide confirmation. In the first place, it is not clear that we can encapsulate the information contained in an analogical argument in a single proposition, \(E\). Second, even if we can formulate a proposition \(E\) that expresses that information, it is typically not appropriate to treat it as evidence because the information contained in \(E\) is already part of the background, \(K\). This means that \(E \cdot K\) is equivalent to \(K\), and hence \(Pr(H \mid E \cdot K) = Pr(H \mid K)\). According to the Bayesian definition, we don’t have confirmation. (This is a version of the problem of old evidence; see confirmation .) Third, and perhaps most important, analogical arguments are often applied to novel hypotheses \(H\) for which the prior probability \(Pr(H \mid K)\) is not even defined. Again, the definition of confirmation in terms of Bayesian conditionalization seems inapplicable.

If analogies don’t provide inductive support via ordinary conditionalization, is there an alternative? Here we face a second difficulty, once again most easily stated within a Bayesian framework. Van Fraassen (1989) has a well-known objection to any belief-updating rule other than conditionalization. This objection applies to any rule that allows us to boost credences when there is no new evidence. The criticism, made vivid by the tale of Bayesian Peter, is that these ‘ampliative’ rules are vulnerable to a Dutch Book . Adopting any such rule would lead us to acknowledge as fair a system of bets that foreseeably leads to certain loss. Any rule of this type for analogical reasoning appears to be vulnerable to van Fraassen’s objection.

There appear to be at least three routes to avoiding these difficulties and finding a role for analogical arguments within Bayesian epistemology. First, there is what we might call minimal Bayesianism . Within the Bayesian framework, some writers (Jeffreys 1973; Salmon 1967, 1990; Shimony 1970) have argued that a ‘seriously proposed’ hypothesis must have a sufficiently high prior probability to allow it to become preferred as the result of observation. Salmon has suggested that analogical reasoning is one of the most important means of showing that a hypothesis is ‘serious’ in this sense. If analogical reasoning is directed primarily towards prior probability assignments, it can provide inductive support while remaining formally distinct from confirmation, avoiding the logical difficulties noted above. This approach is minimally Bayesian because it provides nothing more than an entry point into the Bayesian apparatus, and it only applies to novel hypotheses. An orthodox Bayesian, such as de Finetti (de Finetti and Savage 1972, de Finetti 1974), might have no problem in allowing that analogies play this role.

The second approach is liberal Bayesianism : we can change our prior probabilities in a non-rule-based fashion . Something along these lines is needed if analogical arguments are supposed to shift opinion about an already existing hypothesis without any new evidence. This is common in fields such as archaeology, as part of a strategy that Wylie refers to as “mobilizing old data as new evidence” (Wylie and Chapman 2016: 95). As Hawthorne (2012) notes, some Bayesians simply accept that both initial assignments and ongoing revision of prior probabilities (based on plausibility arguments) can be rational, but

the logic of Bayesian induction (as described here) has nothing to say about what values the prior plausibility assessments for hypotheses should have; and it places no restrictions on how they might change.

In other words, by not stating any rules for this type of probability revision, we avoid the difficulties noted by van Fraassen. This approach admits analogical reasoning into the Bayesian tent, but acknowledges a dark corner of the tent in which rationality operates without any clear rules.

Recently, a third approach has attracted interest: analogue confirmation or confirmation via analogue simulation . As described in (Dardashti et al. 2017), the idea is as follows:

Our key idea is that, in certain circumstances, predictions concerning inaccessible phenomena can be confirmed via an analogue simulation in a different system. (57)

Dardashti and his co-authors concentrate on a particular example ( Example 17 ): ‘dumb holes’ and other analogues to gravitational black holes (Unruh 1981; Unruh 2008). Unlike real black holes, some of these analogues can be (and indeed have been) implemented and studied in the lab. Given the exact formal analogy between our models for these systems and our models of black holes, and certain important additional assumptions, Dardashti et al. make the controversial claim that observations made about the analogues provide evidence about actual black holes. For instance, the observation of phenomena analogous to Hawking radiation in the analogue systems would provide confirmation for the existence of Hawking radiation in black holes. In a second paper (Dardashti et al. 2018, Other Internet Resources), the case for confirmation is developed within a Bayesian framework.

The appeal of a clearly articulated mechanism for analogue confirmation is obvious. It would provide a tool for exploring confirmation of inaccessible phenomena not just in cosmology, but also in historical sciences such as archaeology and evolutionary biology, and in areas of medical science where ethical constraints rule out experiments on human subjects. Furthermore, as noted by Dardashti et al., analogue confirmation relies on new evidence obtained from the analogue system, and is therefore not vulnerable to the logical difficulties noted above.

Although the concept of analogue confirmation is not entirely new (think of animal testing, as in Example 8 ), the claims of (Dardashti et al. 2017, 2018 [Other Internet Resources]) require evaluation. One immediate difficulty for the black hole example: if we think in terms of ordinary analogical arguments, there is no positive analogy because, to put it simply, we have no basis of known similarities between a ‘dumb hole’ and a black hole. As Crowther et al. (2018, Other Internet Resources) argue, “it is not known if the particular modelling framework used in the derivation of Hawking radiation actually describes black holes in the first place. ” This may not concern Dardashti et al., since they claim that analogue confirmation is distinct from ordinary analogical arguments. It may turn out that analogue confirmation is different for cases such as animal testing, where we have a basis of known similarities, and for cases where our only access to the target domain is via a theoretical model.

In §3.6 , we saw that practice-based studies of analogy provide insight into the criteria for evaluating analogical arguments. Such studies also point to dynamical or programmatic roles for analogies, which appear to require evaluative frameworks that go beyond those developed for analogical arguments.

Knuttila and Loettgers (2014) examine the role of analogical reasoning in synthetic biology, an interdisciplinary field that draws on physics, chemistry, biology, engineering and computational science. The main role for analogies in this field is not the construction of individual analogical arguments but rather the development of concepts such as “noise” and “feedback loops”. Such concepts undergo constant refinement, guided by both positive and negative analogies to their analogues in engineered and physical systems. Analogical reasoning here is “transient, heterogeneous, and programmatic” (87). Negative analogies, seen as problematic obstacles for individual analogical arguments, take on a prominent and constructive role when the focus is theoretical construction and concept refinement.

Similar observations apply to analogical reasoning in its application to another cutting-edge field: emergent gravity. In this area of physics, distinct theoretical approaches portray gravity as emerging from different microstructures (Linneman and Visser 2018). “Novel and robust” features not present at the micro-level emerge in the gravitational theory. Analogies with other emergent phenomena, such as hydrodynamics and thermodynamics, are exploited to shape these proposals. As with synthetic biology, analogical reasoning is not directed primarily towards the formulation and assessment of individual arguments. Rather, its role is to develop different theoretical models of gravity.

These studies explore fluid and creative applications of analogy to shape concepts on the front lines of scientific research. An adequate analysis would certainly take us beyond the analysis of individual analogical arguments, which have been the focus of our attention. Knuttila and Loettgers (2014) are led to reject the idea that the individual analogical argument is the “primary unit” in analogical reasoning, but this is a debatable conclusion. Linneman and Visser (2018), for instance, explicitly affirm the importance of assessing the case for different gravitational models through “exemplary analogical arguments”:

We have taken up the challenge of making explicit arguments in favour of an emergent gravity paradigm… That arguments can only be plausibility arguments at the heuristic level does not mean that they are immune to scrutiny and critical assessment tout court. The philosopher of physics’ job in the process of discovery of quantum gravity… should amount to providing exactly this kind of assessments. (Linneman and Visser 2018: 12)

Accordingly, Linneman and Visser formulate explicit analogical arguments for each model of emergent gravity, and assess them using familiar criteria for evaluating individual analogical arguments. Arguably, even the most ambitious heuristic objectives still depend upon considerations of plausibility that benefit by being expressed, and examined, in terms of analogical arguments.

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Other Internet Resources

• Crowther, K., N. Linnemann, and C. Wüthrich, 2018, “ What we cannot learn from analogue experiments ,” online at arXiv.org.
• Dardashti, R., S. Hartmann, K. Thébault, and E. Winsberg, 2018, “ Hawking Radiation and Analogue Experiments: A Bayesian Analysis ,” online at PhilSci Archive.
• Norton, J., 2018. “ Analogy ”, unpublished draft, University of Pittsburgh.
• Resources for Research on Analogy: a Multi-Disciplinary Guide (University of Windsor)
• UCLA Reasoning Lab (UCLA)
• Dedre Gentner’s publications (Northwestern University)
• The Center for Research on Concepts and Cognition (Indiana University)

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Writing An Analogy

TIP Sheet WRITING AN ANALOGY

An analogy is an extended comparison between two things usually thought of as unlike. Analogies illustrate and explain by moving from the familiar to the unfamiliar, comparing several points, each of which has a counterpoint. For example, here is an analogy in which an engineering student explains something relatively unknown (loading a tanker) by using her knowledge of something known (filling pop bottles):

A tank truck usually holds between 4,000 and 6,000 gallons of gasoline. Depending on the tanker, three to six individual compartments hold 600 to 900 gallons of gasoline apiece. The tank that contains the compartments is elliptically shaped to distribute the pressure equally and to allow a more complete flow of air when the gasoline is delivered.

Until recently the only way to load a tanker was to climb up on top, where the openings to the compartments are located. You can easily picture this by visualizing six pop bottles lined up in single file on a table. A man wants to fill up bottle three, so he takes the cap off. He then inserts a small hose into the neck of the bottle and turns on a faucet which is connected to the hose.

A gasoline tanker is loaded in a similar way, but on a much larger scale. A man climbs on top of the tanker and opens a particular compartment by removing the cap. He then takes a hose with a four-foot metal pipe down into the "bottle" (the compartment hole), which measures four inches in diameter. A pump is then turned on, allowing the gasoline to flow into the compartment.

Know your audience In the (admittedly unlikely) event her readers had no prior knowledge of pop bottles, however, this analogy might not be particularly informative. The writer chose this analogy based on the likely knowledge of her audience. When you construct an analogy, be certain that the familiar or known side of the analogy is really familiar and known to your reader. It is useless to explain a mineral's crystal-lattice structure by reference to analytic geometry if your reader knows nothing about analytic geometry.

All of us know many things that we can use to help a reader understand an idea better. Here a geology major shows how the oil seismograph works by comparing it to shouting at a cliff wall:

The oil seismograph is a small portable electronic instrument that detects and measures artificial earthquakes. The purpose of the instrument is to find geological structures that may contain oil. The oil seismograph instrument is not mysterious because it can be compared to shouting at a cliff wall.

Imagine yourself standing near the base of a large cliff. If you shout at the cliff face, you will get an echo because the sound waves bounce back from the "interface" where air meets rock. The sound waves travel at 1,100 feet per second. You can find out how far you are standing from the cliff by measuring the time it takes for your shout to travel from you to the cliff and back again, and then by solving a simple formula for distance.

The function of the oil seismograph is to find out how far down in the earth the horizontal layers of rock are. To discover this distance, the oil seismologist digs a deep hole (usually 100-200 feet). At the bottom of the hole, he explodes a heavy charge of dynamite. Ground waves travel from the explosion down to the layers of rock. At each major interface between the layers, the waves bounce back to the surface. The explosion is similar to shouting at the cliff. Just as sound travels through the air at a certain speed, ground waves travel through the earth, although much faster. Ground waves bounce from rock interfaces as sound waves bounce from a cliff face. And the seismologist can determine distance just as you can determine the distance between you and the cliff.

Know your limits It is said that all analogies limp, that is, they are useful for illustration only as far as they remain reasonable. Therefore, do not try to stretch an analogy too far. Like the fabled camel who first put his nose in the man's tent, then his head and finally his whole body, pushing the man out of the tent, analogies can get out of control unless you know when to stop. Cut out or explain any points that cannot be logically compared.

For example, it might be a fair analogy to say that some professional athletes are treated like kings, that they receive special homage from the public and exemption from some rules, that they are more an expense and a pampered group than an asset to the community. But, except for comic effect, it would be overstatement to compare the equestrian charge of a king at an enemy with a football lineman's charge from the line of scrimmage. Likewise, it would be ridiculous to claim that modern athletes believe themselves divinely ordained to lead their country, or that professional athlete-ship is handed down from father to son by divine right. Just because certain similarities between athletes and kings exist, it doesn't follow that every kingly attribute manifests in modern-day athletes. Do not overconnect the subjects being compared.

Good analogies are vivid and logical, and while they cannot prove an argument, they can offer a picture that is very persuasive.

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The simile, the metaphor, and the analogy are some of the most common literary devices , giving writers the tools to compare different ideas, concepts, and experiences. Yet, because these three devices are all comparisons, it can be difficult to keep track of which device means which. What is a simile vs. metaphor vs. analogy?

Whether you write poetry, fiction, or nonfiction, your writing will drastically improve with the use of these literary devices. Understanding the conundrum of simile vs. metaphor will sharpen the impact of your words, while developing a proper analogy will help you develop a much stronger argument.

This article aims to give you mastery over these essential literary devices, with definitions, examples, and writing exercises for each device. With a deep understanding of simile vs. metaphor vs. analogy, your writing will take on new depth and clarity. Let’s dive in!

Simile vs Metaphor vs Analogy: Contents

Simile Examples

Simile writing exercises, metaphor examples, wielding metaphor effectively.

• Simile Vs Metaphor Examples

The Extended Metaphor

Metaphor writing exercises, analogy examples, analogy writing exercises, side by side: simile vs. metaphor vs. analogy, simile definition: the indirect comparison.

The words “simile” and “similar” come from the same root, and that’s exactly what a simile is: a comparison of similar things.

Specifically, a simile compares two or more items using “like,” “as,” or another comparative preposition. Also known as an “indirect comparison,” the simile allows writers to explore the many facets of complex ideas.

A simile compares two or more items using “like,” “as,” or another comparative preposition.

Take these three simile examples:

• My cat is as loud as Yankee Stadium .
• My cat is soft and fluffy, like a teddy bear .
• My cat destroys furniture the way bulldozers destroy buildings .

These similes offer very different descriptions, yet coexist quite peacefully in my cat—who is, in fact, loud and soft and destructive.

Here are some more simile examples, all of which come from published works of literature.

•  “In the eastern sky there was a yellow patch like a rug laid for the feet of the coming sun” — The Red Badge of Courage , by Stephen Crane

By portraying the color of the horizon like a rug, this simile makes the sun seem regal and majestic. This is also a great example of “show, don’t tell” writing , because we know the sun is rising without being told it’s dawn.

• “The world will burst like an intestine in the sun” — “ Passengers ” by Denis Johnson

What an uncomfortable image! Would you believe this simile is the first line of a sonnet? Comparing the world to a “burst intestine” adds a visceral quality to the poem, as it treats the world as a living organism in peril. Additionally, the words “burst” and “intestine” have a slimy sound to them, making this simile both disturbing and intriguing.

• “You lived your life like a candle in the wind” — “Candle in the Wind” by Elton John (lyrics by Bernie Taupin)

This simile is deceptively simple because it paints a complex image. How does a candle react to the wind? Sometimes it flickers, sometimes it stands even taller, and sometimes it wanes to an ember, waiting for the weather to pass.

Bernie Taupin, Elton John’s co-songwriter, wrote the lyrics for “Candle in the Wind” to commemorate the life of Marilyn Monroe, but although the song is specific to one person, the simile could apply to anyone, demonstrating the simple power of this literary device.

It’s your turn to write some similes! A simile should be concise yet expressive, stimulating the reader’s mind without “spoon feeding” a certain interpretation. As you work through these exercises, keep your simile examples descriptive, yet open-ended.

1. Simile Comparison Lists

On a blank piece of paper, create two lists, with each list containing 6 items.

In one list, jot down six different abstract nouns. An abstract noun is something that doesn’t have a physical presence: words like “love,” “justice,” “anger,” and “envy” are all abstract. Words that end in -ism are usually abstract, too, like “solipsism,” “capitalism,” and “antidisestablishmentarianism.”

In the other list, jot down six different concrete nouns. These are nouns that you can touch or observe—so, even though you can’t touch the planet Neptune, it’s still concrete and observable. Try to use nouns that are in most peoples’ vocabularies: the reader is much more likely to know what a basketball is than what a chatelaine is.

For reference, your list might look like this:

Now, connect each abstract noun to a random concrete noun. Try not to be too intentional about which nouns you connect: the point is to compare two different items at random.

Once you’ve connected your two lists, it’s time to write! You’re going to write six similes, one for each pair of nouns. Your similes will use the concrete noun to describe the abstract noun, offering a deeper understanding of that abstract noun.

For example, I might connect the words “anger” and “pencil sharpener.” The goal is to offer a deeper understanding of “anger” through visual description, so I might write the following simile:

• “Anger, like a pencil sharpener , made my words precise while grinding me to dust.”

Write a simile for every noun pair in your list, and see what you come up with! This exercise might spark an idea for a poem, give you a powerful line for a short story, or simply juice your creativity.

2. Simile Poetry

Something wonderful about similes is their versatility. The same object can be described through a series of similes, each simile building off of each other to build a full and complex image.

There’s even such a thing as simile poetry, which is exactly what it sounds like: a poem consisting of similes. Read the poem Surety by Jane Huffman , which abounds with great simile examples.

The goal of this exercise is to write your own simile poem. We’ll follow a simple four step process to do this.

First, select an object or concept that you want to write about. You have free range here: select something as trivial as a spoon, as complicated as time travel, or as abstract as godhood.

Second, generate a list of nouns. Set a timer for 2 minutes and write down as many nouns as you can think of. Try to stick to concrete nouns, as abstract nouns will prove harder to write with.

Third, write some similes! Compare the topic of your poem to each of the nouns you just listed. You don’t have to use every noun, as there might be nouns in your list that have nothing in common with your topic. The goal is to create strong, impactful similes, each of which demonstrate a different facet of the complex idea you’re writing about.

Fourth, assemble your poem. You can write a poem entirely out of similes the way Jane Huffman did, or you can use these similes strategically, like how Kyle Dargan uses the simile to write his ghazal Points of Contact .

Metaphor Definition: The Direct Comparison

The word “metaphor” comes directly from the Greek word metaphora , “a transfer.” That’s exactly what metaphors do: they transfer identities, altering the reader’s understanding of the nature of something.

A metaphor is a statement in which two items, often unrelated, are treated as the same thing. Also known as a “direct comparison,” metaphors can create powerful imagery and description, deepening the meaning of objects and ideas.

A metaphor is a statement in which two things, often unrelated, are treated as the same thing.

Rather than using “like” or “as” like similes do, metaphors are statements of being, often using words like “is,” “are,” and “became” to make a comparison. Metaphors can also make a comparison without using “being verbs” or other comparison words. Take these three metaphor examples, each of which draw a portrait without using excessive language:

• The grandfather clock is king of the family room furniture .
• The grandfather clock became a death knell for her childhood .
• The grandfather clock had the face of an estranged lover. 

Let’s address what each of these metaphors accomplish. The first metaphor shows us the clock’s size and importance; the second metaphor shows us the clock’s ominous presence, focusing on its sound; the third metaphor treats the clock as forlorn and solitary.

In other words, each of these metaphors express the relevance of the grandfather clock without stating it explicitly. Such is the beauty of metaphors: the ability to tell a story through proximity.

Before we offer some more metaphor examples, we need to discuss two important facets of metaphor writing, especially as they relate to simile vs. metaphor.

First, metaphors rely on the suspension of disbelief—in other words, the reader knows they’re being lied to, but accepts it anyway. Obviously, a clock cannot be a king, nor can it be a death knell or a lover… it’s a clock, after all. Nonetheless, the reader accepts what is being told to them because they trust that the metaphor, and what it conveys, is relevant to the text . Metaphors can be imaginative—magical, even!—but they must be relevant.

The metaphor is more “complete” than the simile.

Second, the metaphor is much more “complete” than the simile. If I was actually writing about a grandfather clock, I would only choose one metaphor and stick with it. Multiple metaphors will contradict each other because they’re creating different statements of being . The reader will inevitably wonder if the clock is actually a king, a death knell, or neither, and this thought process will end up disrupting the reader’s suspension of disbelief. This type of writing is known as a mixed metaphor.

Now, let’s see some more metaphor examples!

The following metaphor examples all come from published works of literature.

• “Whatever causes night in our souls may leave stars.” — Ninety-Three by Victor Hugo

Sometimes, the simplest metaphors carry the most complex meanings. The premise of this direct comparison is easy to understand: the things that trouble us now may strengthen us later. At the very least, those stars are twinkles of wisdom that we gain from life experience, illuminating our paths forward, if dimly.

Yet, the operative word in this metaphor is “may.” The things that trouble us might strengthen us, but they might also create an eternal dusk. And, even with starshine, our souls can very much be blanketed by night.

What emerges from this metaphor is a bittersweet rumination on life and its many perils. Accruing wisdom is always a choice, but faith in the light is vital for anyone to push forward.

• But, look, the morn, in russet mantle clad, Walks o’er the dew of yon high eastern hill. — Hamlet by William Shakespeare

This metaphor is a form of personification, a literary device in which nonhuman objects are given humanlike qualities. Specifically, Shakespeare is comparing the sunrise to that of a person, dressed in “russet” red, walking up a hill.

It’s a simple and beautiful comparison. Instead of saying “the sunrise is red,” Shakespeare personifies the dawn itself, showing us its russet color, its slow ascent, and the morning dew that flecks each blade of grass.

• “I’d like to start a bonfire in my heart but today there’s just a stone; last night, a whirlwind; before, a broken mirror.” —” Hope Poems ” by Jill Robbins

The metaphor  here accomplishes several things, but first, we should note that there are several different metaphors here. Every metaphor has two components: the subject, and the thing that subject is being compared to. (These are known as the “tenor” and the “vehicle,” which we’ll explain in the next section.)

So, the subject (tenor) of this metaphor is the speaker’s heart, and the comparisons (vehicles) are a bonfire, a stone, a whirlwind, and a broken mirror.

Each of these objects describe something different about the speaker’s heart. She would like her heart to be a bonfire—a symbol of passion and livelihood. Instead, her heart is a series of objects that cannot catch fire, with each object symbolic of something else. A stone might symbolize heavy and immovable emotions; a whirlwind might represent the speaker’s capricious feelings; a broken mirror might reflect the speaker’s fragmented sense of self.

“But wait! Isn’t that a mixed metaphor?” Yes—but it’s a mixed metaphor that works . The series of incongruent symbols gives the reader a window into the speaker’s heart. By comparing each symbol to the speaker’s desired “bonfire heart,” the reader recognizes the many emotions preserved in each image.

Aristotle said:

“The greatest thing by far is to be a master of metaphor. It is the one thing that cannot be learned from others; it is also a sign of genius, since a good metaphor implies an eye for resemblance.” (“De Poetica,” 322 B.C.)

So how can you be a genius?

In a metaphor, one thing is likened to another. Vivid metaphors are considered a mark of good writing. Since a metaphor disregards logic—an object cannot be something else and be itself at the same time—some consider it “superior” to the simile (though there are plenty of superior similes out there).

“Bear in mind That death is a drum Beating for ever Till the last worms come To answer its call.” From “ Drum ” by Langston Hughes

“No man is an island.” John Donne

“Her face is common property.” From “The Bloody Chamber” by Angela Carter

Good metaphors can become, if they grow to be well known, clichés . (Clichés are “dead metaphors.”) Clichés dull your writing. They become almost invisible to the reader. How do you know your metaphor is a cliché? Other than being well read, you can acquaint yourself with lists from a number of books or check Web sites like Cliché Finder .

Another “bad” metaphor is one that is “mixed.” In a mixed metaphor, the parts of the comparison don’t match. They can be funny, but you don’t want them popping up in your serious writing. Examples of mixed metaphors include:

“It’s deja vu all over again.” “The flood of students flew out the doors.” “The insult cut her like a knife; it froze her in mid-sentence.”

There’s also a danger in using metaphor badly and not even realizing we are using metaphors. Jack Lynch, in his “Guide to Grammar and Style” cites this “more or less realistic example of business writing”:

We were swamped with a shocking barrage of work, and the extra burden had a clear impact on our workflow.

“Let’s count the metaphors,” writes Lynch, “we have images of a marsh (swamped), electrocution or striking (shocking), a military assault (barrage), weight (burden), translucency (clear), a physical impression (impact), and a river (flow), all in a mere twenty words. If you can summon up a coherent mental image including all these elements, your imagination’s far superior to mine.”

Lynch then gives a real example from “The New York Times” (11 June 2001):

Over all, many experts conclude, advanced climate research in the United States is fragmented among an alphabet soup of agencies, strained by inadequate computing power and starved for the basic measurements of real-world conditions that are needed to improve simulations.

Lynch: “Let’s see: research is fragmented among soup (among?); it is strained (you can strain soup, I suppose, but I’m unsure how to strain research); and it is starved — not enough soup, I suppose. Or maybe the soup has been strained too thoroughly, leaving people hungry. I dunno.

The moral of the story: pay attention to the literal meaning of figures of speech and your writing will come alive.”

Using metaphors is much more than writing “something is something else.” Using a sustained metaphor that is neither over-extended nor mixed can be effective: We dived into the debate, sank our serrated teeth into their arguments, tore their ideas into bloody shreds, and then swam away to digest our prey

Use metaphors:

• As verbs: The song ignited his lust but snuffed out her interest.
• As adjectives and adverbs: Her carnivorous brush ate up the canvas.
• As prepositional phrases: The old man considered the scene with a blue-white vulture’s eye.
• As appositives or modifiers: On the stairs he stood, a gawking scarecrow.

Simile vs. Metaphor Examples

What is the difference between a simile and a metaphor? There are a few key traits that separate simile vs. metaphor, and understanding them will help you decide which device to use in your work.

Let’s look at the key differences between simile vs. metaphor, and how these differences affect the meaning of each device.

Simile vs. Metaphor: Comparison Words

A simile will always use a comparison word. The most common of these comparison words are “like” and “as,” but there are other ways of denoting comparison, too. The following statements mean virtually the same thing, but use slightly different terms of comparison:

• The elephant sat still, like a statue.
• The elephant sat as still as a statue.
• The elephant sat still the way statues do.

Metaphors, on the other hand, rely on various forms of the verb “to be”—if they use a comparison word at all. Metaphors can also be implied through punctuation and word choice. All of the following are proper constructions for the metaphor:

• The elephant was a statue amongst the trees.
• The elephant had petrified at the sight of the tiger; a statue of instinct.
• The elephant: a marble statue.

You could even make the noun “marble” a verb, though some traditionalist writers dislike the grammar behind this. Nonetheless, “the elephant was marbled at the sight of the tiger” offers a unique image.

Simile vs. Metaphor: Differences of Intensity

When a simile compares two or more items, each item retains their individual meanings. For example, if I said “this pancake is as thick as a Dostoevsky novel,” you can visualize the thickness of both items while still imagining two different objects, the pancake and the book. The simile is humorous while still being descriptive.

With metaphors, the object of comparison takes on a different image. If I said “this pancake is a Dostoevsky novel,” you would envision a pancake about 1,000 pages thick. Sounds delicious!

Here’s a metaphor and a simile side-by-side. Take note of how your mental image differs between these two sentences.

• The little boy clings to his mother like ivy clings to a tree.
• He was an ivy growing up his mother’s legs.

Simile vs. Metaphor: Degree of Magic

Yes, magic! Because metaphors are statements of being (whereas similes are statements of likeness), a metaphor can rely on visual descriptions that aren’t bound by the laws of logic. An elephant can be marble, a boy can be ivy, and my cat is (and always will be) a bulldozer.

Similes, by contrast, cannot make statements quite as “magical” in nature. While you might make comparisons to mystical items with a simile—“she waved her flag like a magic wand”—there are still two distinct objects at the end of the sentence, not one magically combined idea.

As we’ve discussed, it is much harder to describe one thing using multiple metaphors. This will inevitably result in a mixed metaphor, which, unless very tactfully written, will confuse the reader instead of enlighten them.

However, another device you can put in your literary toolbox is the extended metaphor. Sometimes synonymous with the literary device conceit , the extended metaphor allows you to explore the implications of the metaphor you just wrote.

The extended metaphor allows you to explore the implications of the metaphor you just wrote.

Let’s start with a simple metaphor:

• Her heart splashed on the asphalt alongside the rain.

The comparison here is easy to understand, and in fact, this metaphor could stand on its own quite easily. But it can also be expanded to say more about the life cycle of a broken heart.

Extended metaphors exist in both prose and poetry . For now, let’s use prose.

• Her heart splashed on the asphalt alongside the rain. Imagine: a torrent you just can’t quench, eddies of water and heartache iridescing towards the drain pipes. When does the feeling quit gushing through sewage systems and underground rivers? When does the water simply calm down? The heart, it sublimates; the heart, it fizzles and gas-ifies and clouds. Whoever said love is eternal was lying: love is a rain cycle. Our hearts, unstudied weather patterns—precipitating.

For examples of extended metaphor in literature, take a look at these poems.

• Hope is the thing with feathers by Emily Dickinson
• Landscape with Fruit Rot and Millipede by Richard Siken
• Habitation by Margaret Atwood

Ready to try your hand at the metaphor? These two exercises will help you write sharp, polished direct comparisons.

1. Very-Extended Metaphors

To begin this writing exercise, simply come up with two concrete nouns. You will compare one noun to the other, so try to keep your nouns unrelated to each other, so that you come up with more striking language. For example, don’t use “apples and oranges”, but “elephants and statues” will be perfectly different from each other.

Once you have two concrete nouns, set a timer for 10 minutes.

When the timer starts, write down all of the ways that Noun 1 can be Noun 2. Just jot your ideas down; don’t try to write anything “polished.” For example, an elephant is a statue because elephants can stand perfectly still, some are creamy white, both elephants and statues pose, etc.

When the timer stops, go over everything you wrote down. Examine the different reasons that Noun 1 is Noun 2, and start weaving sentences together to build an extended metaphor. Let each comparison have its own sentence, building an argument through metaphor. Be visual with your description: show the reader how Noun 1 is the same thing as Noun 2. When you’ve woven these ideas together, you’ll have an extended metaphor, which could become part of a poem or prose piece.

2. Opposites Attract, Metaphorically

For this metaphor exercise, think of two concrete nouns that are either opposites or near-opposites.

For example, “trees” and “factories” can be considered near-opposites. One is natural and produces oxygen, the other is man-made and produces carbon dioxide.

How can a tree be a factory? How can a factory be a tree? These questions are best answered in metaphor.

Write a metaphor using the two opposing nouns you chose, and explain why Noun 1 is Noun 2. The goal is to surprise the reader with a comparison they didn’t expect. This type of writing, when a metaphor joins two unalike or unexpected things, is known as a “conceit.”

Analogy Definition: The Argumentative Comparison

The word “analogy” comes from the Greek, roughly translated to mean “proportional.” Analogies argue that two seemingly different items are “proportional” and, in doing so, build an argument about a larger issue. An analogy might not be the central device of your writing, but analogies can contribute much-needed perspective to an argument, appealing to the reader’s sense of logic.

Analogies argue that two seemingly different items are “proportional” and, in doing so, build an argument about a larger issue.

An analogy has two purposes:

• The identification of a shared relationship, and/or
• The use of something familiar to describe something unfamiliar.

This will make sense with some analogy examples. Let’s start with a simple one:

• Finding a new species of fish is like finding a needle in a haystack.

This analogy identifies a shared relationship between two things: namely, that finding both objects is difficult. Additionally, it uses a familiar phrase—“like a needle in a haystack”—to describe something that the reader might not know about.

Additionally, this sentence structure “A is to B” is common for analogies. You might also see the construction “A is to B as C is to D.”

An analogy can take the form of a simile or metaphor.

Finally, you might be wondering: Isn’t that analogy also a simile? And the answer is: Yes! An analogy can take the form of a simile or metaphor, which is why identifying one from the other can be a bit tricky. In a bit, we’ll discuss the differences between simile vs. metaphor vs. analogy. But first, let’s look at more analogy examples.

All of these analogy examples come from published works of literature. In our analysis, we’ll examine what makes each of these analogies distinct from similes and metaphors.

• “That which we call a rose / By any other name would smell as sweet” — Romeo and Juliet by William Shakespeare

Shakespeare is negating the idea of nominative determinism—the idea that the name of something changes its essential characteristics. The idea of a “sweet smelling rose” is familiar to the reader, and by modifying this idea to call the rose a nameless flower, Shakespeare suggests that the name “rose” has no effect on the rose’s smell.

In Romeo and Juliet , Juliet says this line as part of a larger argument: that her status as a Capulet does not change his love for her, even though he is a Montague. This rejection of family history for the sake of love is central to the play’s tragedy.

• An author who expects results from a first novel is in a position similar to that of a man who drops a rose petal down the Grand Canyon of Arizona and listens for the echo. — Cocktail Time by P. G. Wodehouse

Although his advice is a bit pessimistic, P. G. Wodehouse illustrates his point with a strong analogy. A rose petal will never create an echo, and even if it could, the Grand Canyon is far too deep for anyone to hear it.

Similarly, an author’s first novel probably won’t find resounding success, and even if it does, it will not change the literary landscape on its own. An author needs to put out consequent novels to have a much larger impact—to throw a boulder down the Grand Canyon and hear its echo, metaphorically.

In this analogy, the familiar idea is an echoless rose petal, and the new idea is an author publishing their first book. This analogy could be rewritten in the following way: “a rose petal echoes the way an author’s first book impacts the literary world.”

• As cold water is to a thirsty soul, So is good news from a far country. —Proverbs 25:25

The analogy here is clear and simple: water quenches a parched throat the way good news quenches the soul. The reader is naturally familiar with the feeling of a quenched thirst, making it much easier to understand the sense of relief begat by good news—especially if you’re worried about bad news.

This analogy has a sentence structure common to analogies: “A is to B as C is to D.”

Ready to write your own analogy examples? These two exercises will jumpstart your creativity.

1. Start With a Simile

As you’ve seen in the above analogy examples, many analogies can also be characterized as similes. For this exercise, we’re going to start with similes.

Just as we did in the first simile writing exercise, we’re going to create two lists: a list of concrete nouns, and a list of abstract nouns.

Follow the instructions from our first writing exercise for similes, and when you’ve generated a list of similes, we’re going to turn them into analogies.

How do you turn a simile into an analogy? An analogy has two parts: information that’s familiar to the reader, and information that’s new to the reader.

Let’s say you wrote down the line “his car horn sounds like an electric goose.” The electric goose is familiar to the reader: they can imagine that sound in their head. “His car horn” is not familiar, because the reader hasn’t heard this particular car horn before.

The best way to create an analogy from a simile is to use parallel structure , which means both parts of the analogy are constructed the same. Both the horn and the goose “honks,” which makes “honking” the piece of information most familiar to the reader. If we use parallel structure and rely on common information, we can turn the simile into the following analogy:

“He honks his horn like a goose honks at strangers.”

It’s that simple! Of course, whatever analogies you write, you may decide to expand on them more. Analogies can be arguments on their own, and they can also tie into a larger thesis or idea. However, an analogy should be self-explanatory: the reader should not need additional information to understand it.

2. A is to B as C is to D

All you need for this writing exercise is five words: one verb and two pairs of concrete nouns.

Come up with these words however you like. Use a word generator, create a list, flip to a random page in the dictionary, etc. The only requirement is that two of your four nouns can do the verb. (A dolphin can swim, but it can’t type on a keyboard, for example.)

Your list might look like this:

• Verb: Coddle
• Noun Pairs: mother and son, artist and easel

Once you have these words selected, you have everything you need to write an analogy. Your next step is to put them in the sentence structure “A is to B as C is to D.”

So, for the words I randomly selected, my analogy could read like this: “a mother coddles her son the way an insecure artist coddles his easel.”

And there, I have an analogy! If I wanted to, I could write more about how an artist should let go of micromanaging the canvas, allowing art to develop naturally through the artistic process. However, my analogy makes this argument on its own, which a proper analogy should do.

What do similes, metaphors, and analogies have in common, and how do they differ? We’ve summarized this at the following Venn Diagram comparing simile vs. metaphor vs. analogy.

Simile vs. Metaphor vs. Analogy Venn Diagram

Explore More Literary Devices at Writers.com!

Want to sharpen your language with interesting similes, metaphors, and analogies? The resources at Writers.com can help! Our online writing courses can help you learn the tools of writing and finish your works-in-progress. You can also follow our Instagram and join our Facebook group for weekly writing tips and our one-of-a-kind writing community. We hope to see you there!

Sean Glatch

Thanks, Sean. I’m sure this will be helpful for many writers. I’m sharing on Facebook… and on Twitter.

Thank you so much, Kathy!

Sean, This section was very informative.Could you clarify my doubt?.In the poem Amanda by Robin Klein.. (I am an orphan, roaming the street.

I pattern soft dust with my hushed, bare feet.

The silence is golden, the freedom is sweet.) I am an orphan is stated as a metaphor. A comparison is made between her and an orphan. From what I’ve understood it’s not one as orphan is not an inanimate object.PLease clarify my doubt. Thanks Regards Sanzie

Thanks for your question! Yes, “I am an orphan” is absolutely a metaphor here. Our article mostly sticks to inanimate objects because metaphors with human identities can be tricky to navigate. That said, anything that is a noun can be used in a metaphor. Saying “the grandfather clock is king of the furniture” is also a metaphor using a human identity.

I hope this adds some clarity!

Elton John didn’t write ‘Candle in the Wind’ – that was lyricist Bernie Taupin’s work.

Thank you for this correction! I’ve updated the article accordingly.

Warmest, Sean

This was super helpful! The most descriptive explanation I have found. Thank you!

Thanks, this is helpful Well explained even to my understanding Great impact!

This article is refreshing, like a tall cold lemonade on a scorchingly hot day.

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How To Write An Analogy Essay

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• Author Sandra W.

What Is An Analogy Essay?

An analogy compares two unlike things to illustrate common elements of both. An analogy essay is an extended analogy, which explains one thing in considerable depth by comparing it to another. Analogy essays discuss nearly anything, as long as the writer can find a comparison that fits.

Click Here To Download Analogy Essay Samples

How to use analogies:

• As introductions for papers where you want to show how two ideas are parallel.
• To explain unknown/abstract concepts in terms familiar to or easily understood by your reader. For example when explaining the storage pattern for a Macintosh computer, you might liken the hard drive icon to a large filing cabinet.

Steps For Writing An Analogy Essay

1. Come up with an analogy

 One-half of the analogy is the subject of explanation, while the other half is the explainer. For example, if you said growing up is like learning to ride a bike, you would be explaining something complex and subtle (growing up) in terms of something simple that your audience will be familiar with (riding a bike.)

2. Draw a vertical line down the middle of a piece of paper to divide it in half .

 On one half, write characteristics of the explainer, and on the other half, the explained. Try to match up the characteristics. For example, training wheels might be similar to having to have lots of supervision when you are young.

3. Write a paragraph discussing the explainer .

 Start with a statement like "Growing up is like learning to ride a bike." Then explain the stages of learning to ride a bike.

4. Write a paragraph discussing the explained .

Start with a statement that gives an overview of what the two shares. In the example above, you might say something like "Growing up also involves getting greater and greater freedoms as you become more confident”. Then explain the steps of the explained in a way that parallels the explainer.

5. Discuss the differences .

Sometimes there is a very important aspect of the explained that does not match up with the explainer. For example, in the above essay, you eventually completely learn to ride a bike, but you never stop growing up and learning new things. You may want to draw attention to this important distinction.

6. Review your choice of words for denotation and connotation .

The allure of analogies is such that they can lend themselves to exaggeration. Fight this tendency, as it will only jeopardize your credibility.

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Situation Essay

Situation essay generator.

Have you ever written an essay that involves topics that may not be as common as people perceive them to be? We know for a fact that the most common essay topics are friendship, love and success. However, there are also essays wherein the topics may not be the kind you would think some readers would enjoy. These essays can either touch the hearts of many, or can bring tears to those who read them. In literature and prose, they are called situation essays. What are situation essays and why are they important to learn and understand? Take a look at these examples of a situation essay, which topics like pandemic, ethics and family can be written.

10+ Situation Essay Examples

1. rhetorical situation essay.

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2. Pandemic Situation Essay

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3. Dangerous Situation Essay

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4. Covid 19 Situation Essay

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5. Family Situation Essay

6. situation ethics essay.

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7. Situational Essay on Crime Prevention

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8. Situation Essay on Leadership

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9. Situation Essay On Awareness

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10. Situation Essay on Poverty

11. Sample Situation Essay

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What Is a Situation Essay?

A situation essay is a kind of writing style that you use in order to adapt to what your essay topic is about. You often see this in any kind of essay you will write about. From informative essays , reflective essays , analytical essays , welcome speeches , This kind of writing style helps you adapt or understand the nature of your topic without having to go off topic or having to find a better way to write or address it. Situation essays can be used in just about any form of writing. Just like in emails, speeches, essays, and letters. The main purpose of the situation essay is to provide you the means to appeal to the person or people reading your writing.

How to Write a Situation Essay

Getting an idea on how to write a situation essay should not be that difficult or complicated. All you need to do is to follow simple steps to get there. The important thing to remember is you provide the means to appeal to your audience. Here’s how to do it.

Step 1: Your Introduction Must Catch Their Curiosity

Just like in writing any story, or an email, or even a speech, the most important thing you can do is to make an introduction that catches the reader’s attention and curiosity. Make your introduction something catchy but not too catchy they may lose interest after the introduction. In a way, give them a little taste of what they are going to expect. 

Step 2: Add Something That Relates to the Topic

This is the second part or the second paragraph if you are writing a letter, an email, or even a speech. Think of something that relates to your topic. Not only does this continue to grab your audience’s attention, but it also shows you are able to correlate your introductory topic to your main topic.

Step 3: Be Clear and Concise with Your Writing

Since you are going to be writing about a topic for your essay, there are times that you may forget that you are writing for your audience to appeal to what you are saying. This however does not mean that you should forget to be clear and concise with your topic and your writing. Make sure that you stick to making it clear all the way.

Step 4: Review Your Essay

Before you hand it over to the respective audience, always be sure that every single detail is present in your essay. The topic, the introduction, the statement or purpose of your essay and the conclusion. In addition, part of your review should also be about the grammatical errors, spelling and punctuations.

What is a situation essay?

A situation essay is a kind of writing style that you use in order to adapt to what your essay topic is about. You often see this in any kind of essay you will write about.

What are other kinds of essays or works you can use for this writing style?

The other essays you can use for this writing style are:

• Reflective essay
• Narrative essay
• Formal essays
• Case studies

What are some common topics for a situation essay?

Any topic can be used for a situation essay. You can write about family, friends, romance, personal, business, etc.

Have you ever written an essay that involves topics that may not be as common as people perceive them to be? Situation essays are the type of writing format that gives your readers the opportunity to put themselves in the shoes of the person or character they are reading. This is often used in writing stories, essays or speeches.

Text prompt

• Instructive
• Professional

Situation Essay on the impact of climate change on small island nations

Situation Essay on the ethical considerations of genetic engineering

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The Perils of the Fed’s Vast Bond Holdings

The Federal Reserve is shedding assets at a glacial pace, exposing the financial system to continuing risks, our columnist says.

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By Jeff Sommer

Jeff Sommer writes Strategies , a weekly column on markets, finance and the economy.

The Federal Reserve is engaged in a colossal transformation of the financial economy. Yet scarcely anyone is noticing.

What it’s doing is like walking a herd of elephants through Midtown Manhattan without attracting much attention. That used to happen in New York in the wee hours — when the circus came to town and elephants walked over the city’s bridges and through its tunnels to Madison Square Garden.

I’m not talking about the Fed’s decisions on short-term interest rates, which get the headlines when the central bank meets, as it did on Wednesday. The Fed kept those rates steady — and fairly high — at about 5.33 percent, in a frustrating battle to subdue inflation.

I’m talking about a remarkably ambitious and poorly understood Fed project known as quantitative tightening — Q.T. for short. That refers to the Fed’s reduction of the Treasury bonds and mortgage-backed securities on its mammoth balance sheet.

The central bank said on Wednesday that it would start slowing the pace of this asset paring in June, to $60 billion a month from a maximum reduction of $95 billion a month. It’s not selling securities, just quietly eliminating some as they mature, without reinvesting the proceeds.

These may look like big numbers. Yet on a comparative basis, they are piddling.

Consider that the central bank’s assets peaked two years ago at almost $9 trillion. That sum is roughly one-third of all the goods and services — the gross domestic product — produced in the United States in one year. Now, after much careful effort, the Fed has cut that total to about $7.4 trillion.

Yes, it has removed about $1.6 trillion from its coffers. But even after two years of quantitative tightening, the amount of bonds and securities that the Fed still retains is stupendous.

This is mind-boggling stuff, but a basic understanding of quantitative tightening is important for several reasons:

The policy is affecting financial markets now and making living conditions harder for millions of people — putting upward pressure on the Treasury and mortgage markets and a host of related interest rates, effectively supplementing the monetary tightening that the Fed put in place by raising the short-term federal funds rate.

Quantitative tightening is a perilous operation. Earlier attempts — notably, in 2019 — disrupted financial markets. That could happen again if the Fed is too hasty.

If the Fed acts as slowly as current plans project, it will own trillions in securities for years to come. An experiment begun in the 2008 financial crisis is becoming permanent, endowing the Fed — and whoever controls it — with vast expanded powers.

The slow pace of quantitative tightening is partly responsible for the Fed’s inability to contribute to the national budget.

That’s because the Fed has also raised interest rates, which move in the opposite direction of bond prices. With its own policies, the Fed has reduced the value of its asset holdings. And by now it has inflicted more than $133.3 billion of losses on itself.

Unlike Silicon Valley Bank , which became insolvent last year, the Fed can survive paper losses — but it can’t help the U.S. government reduce staggering deficits.

Quantitative Easing

Q.T. is the inverse of an unorthodox approach to monetary policy known as quantitative easing, adopted by the Fed when Ben S. Bernanke was chair. After the collapse of Lehman Brothers in September 2008, the economy and the markets crashed. Trying urgently to give the economy a stimulative jolt, the Fed lowered interest rates to nearly zero, but that wasn’t enough.

Those were desperate times, and the Fed improvised. Expanding on a program that the Bank of Japan started in 2001, the Fed began large-scale buying of Treasury bonds and mortgage-backed securities.

The idea, as Mr. Bernanke said in his book “ 21st Century Monetary Policy ,” was “to influence private-sector decisions, which don’t usually depend directly on Treasury yields.” The Fed, he added, “expected that lower yields in the Treasury market would result in lower yields elsewhere — for example, on residential and commercial mortgages and corporate bonds.”

In addition, Fed policymakers expected that “lower long-term, private-sector interest rates should stimulate business investment and consumer spending on new cars and houses,” Mr. Bernanke said. “Lower long-term interest rates would also increase the prices of other financial assets, such as stocks, and weaken the dollar, easing financial conditions more broadly.”

All of those things happened.

But what started as a temporary expedient evolved into a regular part of the Fed’s toolbox, one that the Fed has used too frequently, some economists say.

“The analogy is a terrible one, but what the Fed has done is engender an addiction,” Raghuram Rajan, a finance professor at the University of Chicago, said in an interview.

Mr. Rajan, who is a former governor of the Reserve Bank of India and chief economist of the International Monetary Fund, said that U.S. banks had become “addicted to the easy liquidity” associated with the Fed’s expansionary policies, and that weaning them off this flood of money had proved excruciatingly difficult.

It’s revealing to look back at early official Fed commentary. In February 2010, in a statement before the House Committee on Financial Services , Mr. Bernanke said, “The Federal Reserve anticipates that it will eventually return to an operating framework with much lower reserve balances than at present.” His statement was labeled “Federal Reserve’s exit strategy.”

But the Fed never exited its quantitative easing strategy. In fact, Fed records show that when Mr. Bernanke testified in 2010 about an eventual end to quantitative easing, the central bank’s balance sheet contained less than $2.3 trillion in assets. Fourteen years later, the Fed holds more than three times that total, even after its most ambitious “tightening” round to date.

Why Tightening Is Tough

Crises happened, the economy faltered and the Fed engaged in multiple rounds of quantitative easing under Mr. Bernanke and his successors, Janet L. Yellen and Jerome H. Powell , the current Fed chair.

All tried quantitative tightening — which, in early Fed planning, appeared to mean a reversal of the Fed’s active intervention in the bond and mortgage markets, a radical reduction in its holdings and a return to pre-crisis operations. In his 2010 testimony, for example, Mr. Bernanke said the Fed could eventually sell the assets it purchased.

But all these years later, it has not done so. When it is not in emergency-response mode and is trying to return to something resembling “normal,” it has allowed maturing bonds and other securities to slowly “run off” or “roll off,” instead of reinvesting the proceeds, which would maintain the size of its asset stash.

It’s moving at an excruciating pace. A report in April by a group within the New York Federal Reserve Bank projected that even with continued quantitative tightening, the assets on the overall Fed balance sheet will fall no lower than $6 trillion in the next few years — and then begin rising again.

In the past, when the Fed even hinted that it might swiftly shed assets, financial markets buckled. In a news conference on Wednesday, Mr. Powell alluded to the 2019 quantitative tightening effort that led to chaos in the money markets — and an about-face by the central bank. The Fed is now slowing the already stately pace of balance sheet roll-off precisely “so that it doesn’t lead to financial turmoil as it did the last time,” he said.

Simply put, the Fed’s balance sheet has assets on one side and liabilities on the other — and they must balance. When it buys assets, it creates bank reserves out of thin air, and it has been paying banks to keep those reserves deposited at the Fed. The reserves are available for emergencies as well as for routine operations. In periods of quantitative tightening, like this one, both the assets and the reserves shrink — and that has periodically caused major dislocations.

So far in this round, the Fed has been managing the process deftly. Scarcely anyone has noticed it drain more than a trillion dollars from the financial system. Yet by concentrating so much financial firepower in its own hands, the Fed may be assuring that the potential for major flare-ups, and even worse, will always loom.

Jeff Sommer writes Strategies , a weekly column on markets, finance and the economy. More about Jeff Sommer