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)

Submitted by Zuzanna12 on Wed, 28/09/2022 - 10:17


Dear Sir,

Could you please tell me whether after the verb 'need' used as a modal verb may I put the noun? For example, may I say: She need a break or He need resting? Or am I supposed to use only infinitive after 'need' used as a modal?

Thank you in advance.

Hi Zuzanna12,

No, if "need" is a modal verb then it must be followed by another verb. It's usually used in negatives or questions, e.g. "Need she work until late?" or "He needn't work until late".

I hope that helps.


The LearnEnglish Team

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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!