Modals – permission and obligation

Do you know how to use modal verbs to talk about permission and obligation?

Look at these examples to see how can, can't, must, mustn't, have to and don’t have to are used.

You can put your shoes and coat over there.
You can't leave your bike there.
I must call the electrician and get that light fixed.
You mustn't worry about me. I'll be fine.
You have to have a licence to drive a car.
You don't have to have a licence to cycle on the roads.

Try this exercise to test your grammar.

Grammar test 1

Modals – permission and obligation: Grammar test 1

Read the explanation to learn more.

Grammar explanation

We often use verbs with modal meanings to talk about permission and obligation.



We often use can to ask for and give permission.

Can I sit here?
You can use my car if you like.
Can I make a suggestion?


We also use could to ask for permission (but not to give it). Could is more formal and polite than can.

Could I ask you something?
Could I interrupt?
Could I borrow your pen for a moment, please?


May is the most formal way to ask for and give permission.

May I see your passport, please?
Customers may request a refund within a period of 30 days.
These pages may be photocopied for classroom use.


We use can't and mustn't to show that something is prohibited – it is not allowed.


We use can't to talk about something that is against the rules, particularly when we didn't make the rules.

What does this sign say? Oh, we can't park here.
You can't take photos in the museum. They're really strict about it.
Sorry, we can't sell knives to under-18s.

must not/mustn't

We use must not to talk about what is not permitted. It is common on public signs and notices informing people of rules and laws.

Visitors must not park in the staff car park.
Baggage must not be left unattended.
Guests must not make noise after 10 p.m.

We use mustn't particularly when the prohibition comes from the speaker.

(Parent to child) You mustn't say things like that to your sister.
(Teacher to student) You mustn't be late to class.
I mustn't let that happen again.


We use have to and must to express obligation. There is a slight difference between the way we use them.

have to

Have to shows us that the obligation comes from outside the speaker. 

We have to wear a uniform when we're working in reception.
(Student to teacher) When do we have to hand in our homework?
Al has to work tomorrow so he can't come.

We sometimes call this 'external obligation'.


Must expresses a strong obligation or necessity. It often shows us that the obligation comes from the speaker (or the authority that wrote the sentence). 

I must phone my dad. It's his birthday today.
(Teacher to student) You must hand in your homework on Tuesday or you will lose ten per cent of your mark.
(Sign on a plane) Seat belts must be worn by all passengers.

Note that we don't use must to express obligation in the past. We use have to instead.

I had to pay £85 to renew my passport last week.

No obligation

don't have to

We use don’t have to to show that there is no obligation. You can do something if you want to but it's not compulsory.

You don't have to wear a tie in our office but some people like to dress more formally.
You don't have to go to the bank to do a transfer. You can do it online.
You don't have to come with me, honestly. I'll be fine!

Do this exercise to test your grammar again.

Grammar test 2

Modals – permission and obligation: Grammar test 2

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Language level

B1 English level (intermediate)
Profile picture for user Ahmed Imam

Submitted by Ahmed Imam on Fri, 31/12/2021 - 17:48


Hello team. Could you please help me? What is the mistake in the following sentence? I think it's correct, right?
- You mustn't water the garden; it's still damp.
Some colleagues say that "mustn't" must be replaced with "needn't".
Thank you.

Hi Ahmed Imam,

Both words are correct, but they mean different things. With "mustn't", the sentence means watering the garden is prohibited or not allowed (e.g. because more water may damage the plants). With "needn't", it means watering the garden is not necessary, and we understand "it's still damp" to mean that there is already enough water there.

The LearnEnglish Team

Profile picture for user Ahmed Imam

Submitted by Ahmed Imam on Mon, 20/12/2021 - 15:39


Hello Team. Could you please help me choose the correct answer? Why?
I am confused if it's an order, law, or external factor, ........
- Employees (must - have to) be on time for work.
Thank you.

Hi Ahmed Imam,

It could be either option. It depends on a couple of things: who is the speaker of this sentence? And on what authority does the speaker assert this?

For example, I would choose "must" if this sentence is written in a handbook for employees (the obligation comes from the handbook writer - the company).

I would choose "have to" if employees say this to each other to remind them to be on time (the employees did not make this rule. They are just repeating it).

If a manager says this to employees, I think either would be acceptable. Using 'have to' means the manager makes the obligation on the basis of the authority of the company's rules. Using 'must' makes the obligation on the basis of his/her own authority as a manager. In practical terms, these are likely to have the same result - to strongly oblige employees to be on time.

I hope that helps.

The LearnEnglish Team

Submitted by BobMux on Mon, 16/08/2021 - 12:59

Hello The LearnEnglish Team, Would you please help me with the sentence below? All drivers must have adequate insurance: it is the law. So, this must be an external obligation and why is the pattern with have + to + verb not used instead of must?

Hello BobMux,

There are several things to remember here.


First, while it's true that we distinguish between external and internal obligation, the correlation of must/internal and have to/external represents a tendency rather than a fixed grammatical rule. In other words, it's not incorrect to use must for external and have to for internal; it's simply less common.


Second, the information on the page describes the use of must as follows: "[Must] often shows us that the obligation comes from the speaker (or the authority that wrote the sentence". In your example, it may be that the sentence was written by/comes from the authority which regulates road use such as the Ministry of Transport, in which case the use of must would be quite normal.

Third, we often try to avoid using have to when the main verb is have, so we tend towards must have rather than have to have. This is a stylistic preference and is again a tendency rather than a rule.



The LearnEnglish Team

Submitted by Sokhom on Wed, 04/08/2021 - 12:53

Hi, sir! e.g. Maybe I'll study in Paris next semester. I submitted my application at the Overseas Studies Office yesterday. They have to / might tell me before May so I can buy my ticket. Personally, I think either 'have to' expressing rules in the organisation or 'might' talking about the possibility is possible in the sentence. Could you please tell me if I am right? I really appreciate it! Best Wish!
Profile picture for user Jonathan R

Submitted by Jonathan R on Wed, 04/08/2021 - 15:33

In reply to by Sokhom


Hi Sokhom,

Yes, I agree that both are grammatically possible in this sentence. However, I guess that have to is more likely to be used. It seems like the speaker is describing the Office's policy or procedure.

If the answer is might (indicating something that's possible but uncertain - i.e., there's a reasonable chance that it will not happen), we must wonder: what will happen if the Office doesn't tell him/her before May? Will he/she be unable to buy a ticket? In a real situation, the speaker would probably go on to comment a bit more about that.

I hope that helps :)


The LearnEnglish Team

Submitted by LitteBlueGreat on Fri, 07/05/2021 - 05:44

Hello sir. Sorry for taking your time but I've recently come across an interesting sentence, here it is "They must not have been found a guilty of criminal offense" yet It makes me puzzling. first of all, I've pondered that to be "Must-- obligation/necessity" but as far i know, there is no grammar construction like the above for "Must--Obligation" except for "Must---Deduction" in which Must + Have + 3rd " is basic of construction... Thus Is that considered as either grammatically error or another usage form? Please help me, Many thanks from me
Profile picture for user Jonathan R

Submitted by Jonathan R on Fri, 07/05/2021 - 11:41

In reply to by LitteBlueGreat


Hi LitteBlueGreat,

No worries :)

Yes, it could be must for deduction. That would mean that, based on some kind of evidence, I have arrived at a conclusion that they have no criminal record (without knowing this 100% for certain).

It could also be must for obligation - or in this case, the negative form, must not for prohibition. For example, it is not allowed for people who have been found guilty of an offense to hold certain jobs, and the sentence may be describing this prohibition. The structure is must (not) + verb, and in this case the verb is a perfect passive (have been) since it refers to an already-completed action of 'being found guilty'. 

To know which of these meanings is intended, we would need to look at the rest of the text where this sentence is used.

Note that the article should be before the noun phrase: ... found guilty of a criminal offense.

I hope that helps.


The LearnEnglish Team

Submitted by Danish ahmedd on Sat, 13/03/2021 - 21:24

Could we use might/may have + verb 3rd form for past possiblity instead of could have +verb 3rd form ? And my second question is that could we use must have +verb 3rd form instead of should have +verb form?

Hello Danish ahmedd,

Yes, 'could have' + past participle and 'may/might have' + past participle can be used to make guesses about the past.

I'm afraid I can't give a simple answer to your second question. All modal verbs have multiple uses. Some of these uses overlap, and so without knowing exactly what you want to say and the situation you intend to say something, I can't really answer your question. What I can say is that 'must have done' and 'should have done' have different meanings. 'must have done', for example, is often used to make deductions about the past, and 'should have done' can be used to speak about something that didn't happen (e.g. 'He should have gone to school' implies that he didn't go to school).

Hope this helps. You're welcome to ask further questions, but please give us specific examples with an explanation of the situation.

All the best,


The LearnEnglish Team

Submitted by Stellaaa on Thu, 24/12/2020 - 11:37

How about "should"? I think should is also mild obligation.Pls explain me

Hello Stellaaa,

We usually speak about 'should' as a way of giving a suggestion rather than communicating an obligation (which is stronger than a suggestion), but it's true that both are similar in that we're telling someone what we think they should do.

All the best,


The LearnEnglish Team

Submitted by Hamdy Ali on Fri, 20/11/2020 - 18:41

You (should-can)read this short story .It is recommended. I think both are correct.What is your opinion?

Hi Hamdy Ali,

Yes! If you want to recommend this short story, both options work. But, should is clearer, as its primary meaning is to show what you think is the right or correct thing to do. (The primary meanings of can are to show ability or possibility.)

Best wishes,


The LearnEnglish Team

Submitted by sindhallb on Thu, 03/09/2020 - 19:15

Hellow , still I need some clarification about using have twice in a sentence

Hello sindhallb,

I'm afraid you'll need to be a bit more specific than that! Can you provide an example sentence which confuses you? We'll be happy to comment.



The LearnEnglish Team

Profile picture for user CHÉKYTAN

Submitted by CHÉKYTAN on Sun, 09/08/2020 - 08:23

I'd love to come to the cinema but I _____ hand in this assignment tomorrow. Why answer is 'have to', not 'must', even though obligation comes from the speaker?

Hi Chekytan,

This sentence would usually be understood as an external obligation – from the lesson, course, school or teacher.

But it is possible that a speaker might feel an obligation from him/herself to hand in an assignment. For example: I must hand in this assignment tomorrow. Otherwise, I won't have time for my other assignments. In this example, the obligation is self-imposed. But without information to suggest that, the obligation in the sentence you mentioned would normally be seen as an external one.

Best wishes,


The LearnEnglish Team

Submitted by Saamongo on Fri, 31/07/2020 - 12:38

We often use can to ask for and give permission. We use could to ask for permission (but not to give it) but what can you tell me about this sentence: "I didn't know you were the headmaster in that office, you could allow me to speak to you then?" Explain me more about the use of could in this sentence and If the sentence is grammatically correct or not. What can COULD express here ?

Hello Saamongo,

I'd say that 'could' in this sentence expresses ability more than permission. You could hear such a sentence in speaking, but in theory the correct word order is 'could you allow me' and in writing it would need to be separated into two sentences.

All the best,


The LearnEnglish Team

Submitted by Inci Ozturk on Thu, 23/07/2020 - 03:23

Airport notice is a kind of obligation announced by legal authority. Then why don't we say "Liquids have to be in 100 ml containers."

Hello Inci Ozturk,

Have to is used to describe regulations, as you say, but it has a factual sense. When giving instructions or commands, must is generally more authoritative and conveys a stronger sense of obligation



The LearnEnglish Team

Submitted by patph0510 on Thu, 16/07/2020 - 15:15

Hi teachers, I read a grammar textbook on the use of "must", and it says that "must" is not used for predictions about the future and “will” should be used instead. However, I saw the following sentence online: I thought the eclipse was today, but it must be happening tomorrow. I would like to ask whether the above sentence is grammatically correct. Thanks!

Heloo patph0510,

The sentence is grammatically correct. We describe this as a deduction rather than a prediction. The speaker is drawing a conclusion about the future on the basis of something they can see in the present.


You can read more about modal verbs used for deduction on these pages:



The LearnEnglish Team

Profile picture for user Karan Narang

Submitted by Karan Narang on Sat, 11/07/2020 - 04:50

People must get up early morning to keep fit their body although we have to do everyday but many of reasons can't be happened by lazy fellow.

Submitted by yoshiyuki on Sat, 23/05/2020 - 04:29

Grammar test2-1 __ go to the party? I'm really tired. Why is the answer 'Can't we' wrong in this question?

Hello yoshiyuki,

The answer is not grammatically wrong but does not fit the context.


Can't we is used when a person wants to do something. For example, a child might ask Can't we have some ice-cream? Please?

In this example, the speaker says that they are really tired, so they would not want to go to the party and would ask if it is really necessary to go. Do we have to... is therefore the correct choice.



The LearnEnglish Team

Submitted by SakshiJulka123 on Sun, 10/05/2020 - 04:19

Hi ! Is the following sentence correct? "She must have realized that people would ultimately come to know that the man had not killed anyone." Thank you. Sakshi
Profile picture for user Kirk

Submitted by Kirk on Mon, 11/05/2020 - 07:59

In reply to by SakshiJulka123


Hello Sakshi

Yes, that is grammatically correct.

All the best


The LearnEnglish Team

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Submitted by OlaIELTS on Thu, 07/05/2020 - 03:11

It's really helpful.