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 (79 votes)

Submitted by nurserin on Wed, 24/04/2024 - 23:22


Hello, I didn't understand 2 examples of on the website.

First example is " a member to buy a ticket. It's open to everyone."

In this sentense why didn't we use "can"?

Second example is "The hostel is totally vegetarian. You...cook or eat meat there."

In this example why didn't we use "don't have to"?

Hi nurserin,

Thanks for your questions!

First, I want to clarify the meaning of "don't have to". It means "it is not necessary", or "it is optional". For example, I can say "I don't have to wear a suit at work", which means I can wear a suit if I want, but there is no obligation to wear a suit. Don't confuse it with "can't", which means "it is not OK" or "it is not allowed".

In the first example, it says "It's open to everyone". So, the main point is that it is not for members only, but also non-members. That's why "don't have to" is the best answer ("You don't have to be a member" = "It is not necessary to be a member" or "There is no obligation to be a member"). 

Since everyone can buy a ticket, it's true to say "You can be a member to buy a ticket". However, the main point is that everyone can buy a ticket, not just members but non-members too. 

In the second example, "don't have to" isn't right because "don't have to" means "it is not necessary". It would be strange for cooking/eating meat in the hostel to be "necessary". Instead, the point is that it's not OK or not allowed to cook/eat meat there (because it's a vegetarian hostel). It's not OK to do that, even if you want to. So, the answer is "can't", which shows something is not allowed or not OK.

Does that make sense?


LearnEnglish team

Submitted by zeynepkaya on Mon, 18/12/2023 - 20:10


Hi, I am confused about using used to and must not. So as far as I understood we can both use must not and cannot for prohibitions. Can you check these examples.

It is not permitted to enter the construction site without a hard hat.
→ You ......... enter the construction site without a hard hat.
It is not allowed to take pictures inside the concert hall.
→ You ........... take pictures inside the concert hall.
It is prohibited to bring outside food into the theme park.
→ You ......... bring outside food into the theme park.

I couldn't decide if they are can't or musn't. Can you explain please?

Hello zeynepkaya,

It is possible to use both 'can't' and 'mustn't' in this sentences. But since they seem to be sentences spoken by someone who is telling another person about the restrictions, it would be more natural to use 'can't'.

In other words, we tend to use 'can't' when we are reporting about restrictions. But on signs or when an authority figure (e.g. an usher in the concert hall or a theme park employee) is speaking, we often use 'mustn't'.

Best wishes,
LearnEnglish team

Submitted by anya1 on Sat, 18/11/2023 - 23:18


Could you please explain the difference between 'may' and 'might'?

Hello anya1,

Both may and might can be used to talk about things we are not sure of in the present and the future. Only may can be used for requests and permission. For example:

John's been working all day so he might/may be tired. [speculation - both are possible]

May I see your ID card, please? [a request - only may is used here]

You can read more on this page:



The LearnEnglish Team

Submitted by hudamaher on Mon, 09/10/2023 - 22:31


I need to know that is there a difference between can't and mustn't?
Thanks in advance.

Hello hudamaher,

There are differences but these are modal verbs which can mean different things in different contexts.

Can't generally means that something is not possible, while mustn't describes rules or choices.

If I say 'You mustn't go in there' then it suggests that it is physically possible for you to enter but it is against the rules, dangerous etc. If I say 'You can't go in there' then it could describe a rule in a similar way but it could also mean that, for example, the door is locked. It depends on the context.

If you have a particular context in mind then we'll be happy to comment.



The LearnEnglish Team

Submitted by smartalex on Tue, 20/06/2023 - 13:24


Why is 'must' the right answer here although it is not an internal obligation? 'Liquids _____ be in 100ml containers and in a closed plastic bag.'

Hello smartalex,

In the explanation for 'must' you can see this sentence:

It [must] often shows us that the obligation comes from the speaker (or the authority that wrote the sentence

In your example 'must' is used because the obligation comes from the authority that wrote the sentence - i.e. whoever sets the rules for air travel. Must is very common in these kinds of rules regarding behaviour in different places (airports, libraries etc).



The LearnEnglish Team