Modals: permission and obligation

Modals: permission and obligation

Do you know how to use modal verbs to talk about permission and obligation? Test what you know with interactive exercises and read the explanation to help you.

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

Language level

Average: 4.1 (86 votes)

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