modal verbs permission

modal verbs

permission and obligation

Permission

can

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?

could

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

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.

Prohibition

We use can't and mustn't to show that something is prohibited

– it is not allowed.

can't

.

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'tWe 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.