you must do your homework now

English Grammar: Modals of Obligation

When we talk about obligation in English, we can use “must”, “have to”, “need to” and “can’t”.

To say something is necessary

We use “must” to talk about obligations. Often, when we use “must”, the authority for the obligation comes from the person who is speaking.

“You must do your homework every night.” (Because I say you must!)

“I must stop smoking!” (Because I think it’s a good idea to stop.)

Remember that “must” is a modal auxiliary verb. This means that it doesn’t change its ending ( I must , he must , etc) and that it’s followed by the infinitive without ‘to’. (“You must phone me” not “You must to phone me”.)

For more information on modal auxiliary verbs, see our page on ability .

We can also use “have to” to talk about rules and regulations. The authority for the obligation doesn’t come from the person who is speaking. Perhaps the rule is a general law or obligation.

“In England you have to pay tax.” “We have to check everyone’s ID.”

“Have to” is a normal verb. Use “do” or “does” to make a question, and “don’t” or “doesn’t” to make a negative.

“Do you have to vote in an election?” “He doesn’t have to wear a uniform to school.”

Have got to

“Have got to” is common in British English and is stronger than “have to”.

“I have got to fill in this form. The deadline is tomorrow.” “She has got to study hard to pass the exam.”

To make the question and negative form, use “have”, “has”, “haven’t” and “hasn’t”:

“Have you got to leave early tomorrow?”

We use “need to” to talk about what is necessary.

“You need to go to the hairdresser’s. Your hair is very long.” “She needs to go to the doctor. She gets headaches every day.”

“Need to” is like “have to”: use do / does to make questions:

“Do you need to pass an exam to get into university?” “Does she need to get a job?”

To say something isn’t an obligation

To say there is no obligation, use “don’t / doesn’t have to” or “don’t / doesn’t need to”.

“You don’t have to bring food on the trip.” “She doesn’t have to work in the evening.”

“I don’t need to pay now. I can pay later.” “They don’t need to speak English in their job.”

Typical grammar mistake! Be careful when you use “don’t have to”. It does not mean the same as “mustn’t” – see below.

To say something is forbidden

To say that there is an obligation not to do something, use “mustn’t”.

“You mustn’t play here – it’s dangerous!” “He mustn’t eat peanuts. He’s allergic to nuts.”

We can also use “can’t”:

“You can’t go out tonight. You’ve got homework.”

Other expressions

be allowed to

“We’re allowed to take an hour for lunch.” “We aren’t allowed to leave early.” “Are you allowed to use the internet at work?

Should is a weak obligation, and we use it to give advice.

“You should study hard so you can pass the exam.” “He should see a doctor.”

The negative form is “shouldn’t”:

“You shouldn’t smoke. It’s bad for your health.”

Modals of Obligation

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Modals - 'must' and 'mustn't'

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Modals – 'must' and 'mustn't'

We can use must and mustn't to talk about rules and obligations.

I must do my homework. We must wear our school uniform. You mustn't be late for class. We mustn't speak when the teacher's speaking.

How to use them

Must means 'Do it!' If you don't do it, you will be in trouble.

You must listen to the teacher.

Mustn't means 'Don't do it!' If you do it, you will be in trouble.

We mustn't forget our books.

Use the infinitive without to after must and mustn't .

Children must respect their parents. Parents must take care of their children. You mustn't shout in the library.

Mustn't mean do not do and must mean you have to do. I'll give you some examples. You must listen to the teacher because if you don't, you don't know what to do. You must wear the correct school uniform. You mustn't be rude to your friends. You mustn't shout in someone's ear.

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Difference Between Should and Must

• Categorized under Grammar | Difference Between Should and Must

Should vs Must

The words “should” and “must” are modal auxiliary verbs or simply modals. They provide information about the function of the main verb following it. Both “should” and “must” are similar in meaning except that “must” is a much stronger word as compared to “should.”

“Should” is the past tense of “shall.”  “Should” is used to denote recommendations, advice, or to talk about what is generally right or wrong within the permissible limits of society. For instance:

• You should chew your food properly.
• We should respect our parents.
• You should stop smoking.
• You must clean our car regularly.

In all these statements, there is a probability or recommendation of some kind.

“Must” is used to talk about an obligation or a necessity. It is used when people are compelled to do something. For instance:

• You must clean the house as your mom is not well.

Here, it is imperative that you clean the house or else the house won’t be cleaned and remain untidy.

• We must obey the law.

This statement compels us to abide by the law or we will have to face the punishment enforced by the law.

• You must hurry if you have to catch the train.

In this statement, it is emphasized that you certainly have to move quickly as you are running late. If you do not hurry up, you will miss the train. This sentence is an example of a compellation for achieving a certain aim.

• One must keep his word.

Here again the sentence directs that people are required to or are compelled to do something (here it is keeping one’s word) by the use of threat or force.

The main difference between the two words “should” and “must” is that “must” is a stronger word, as mentioned before. The probability of “must” is much more than that of “should.” For instance:

• You must do your homework now. (It is already late, and if you do not start doing your work now, you will not be able to finish your work on time. This will lead to punishment or a penalty.)

You should do your homework now. (It is the right time that you start doing your work.)

• You must rest. (You are not well, and if you continue working, your health is going to get worse.)

You should take a rest. (You are tired, and if you do not take a rest, you are going to get sick.)

The synonyms of “should” include: ought, allow, feel, leave, become, suffer, sustain, allow, etc. The synonyms for “must” are: condition, demand, necessity, requirement, requisite, obligation, etc.

• “Must” represents more of an obligation while “should” represents a probability or recommendation.
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Cite APA 7 Kaushik, N. (2016, June 8). Difference Between Should and Must. Difference Between Similar Terms and Objects. https://www.differencebetween.net/language/grammar-language/difference-between-should-and-must/. MLA 8 Kaushik, Nimisha. "Difference Between Should and Must." Difference Between Similar Terms and Objects, 8 June, 2016, https://www.differencebetween.net/language/grammar-language/difference-between-should-and-must/.

15 Comments

awsome explanation good!!!!! . . . . . . . . . 🙂

. . . . . . . . . . . . . . . . <3

thnks 4 telling me the difference……

Well thanks for helping me I was in such a problem doing these type of Qs

Well thanks for helping me

I have such a problem doing these Qs ❤️

Can i write You must take a rest instead of you must rest? Plzzz reply

Yes, you can. You can either write, you must take a rest or you must rest. there is no any difference.

Amazing explanation, I’m delighted for the wonderful explanation done.

Thank you , if we use” should ” in future simple, ‘should’ is stronger than must

can you tell me about should

Very good explanation. Thank you.

Is it right to say an attorney must work to the interest of his clients

should i write one must wearbharonjg tagalog during the independence day or one should wear

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Written by : Nimisha Kaushik. and updated on 2016, June 8 Articles on DifferenceBetween.net are general information, and are not intended to substitute for professional advice. The information is "AS IS", "WITH ALL FAULTS". User assumes all risk of use, damage, or injury. You agree that we have no liability for any damages.

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