can—could—be able to
Can he swim?
My brother could swim when he was two.
I couldn’t find my keys this morning.
I could have run faster, but I didn’t want the others to get tired.
She has not been able to walk since the accident.
He was able to speak to Ann before she left.
Will people be able to live on the moon one day, do you think?
Could/Might you have lost it on the way home?
She may/might/could be ill. I’ll phone her.
I may have/might have left my purse in the shop.
Amy might/may know the answer.
I might/may not go if I’m tired.
He might have enjoyed the party if he’d gone.
It can get very cold in here at night.
Can we come in?
Could we possibly stay at your flat?
Staff may take their break between 12 and 2. (written)
May I sit here? (formal)
You mustn’t tell her anything.
You can’t get up until you’re better.
Crockery may not be taken out of the canteen. (written)
You must not begin until I tell you. (formal)
have (got) to—must
All visitors must report to reception on arrival. (written)
I must get that report finished today.
Do you have to write your name on the form?
She had to throw the burnt cake away.
You will have to wait, I’m afraid.
don’t have to—shouldn’t have—didn’t need to—needn’t have
You don’t have to pick us up–we can take a taxi.
They didn’t have to go through customs.
You shouldn’t have bothered making lunch–we could have bought a sandwich.
He didn’t need to have any fillings at the dentist’s.
They needn’t have waited.
Advice and criticism
Ought we to/Should we write and thank him?
She ought to/should go out more often.
You ought to have/should have gone to bed earlier.
You shouldn’t borrow the car without asking.
I ought to/should go on a diet.
I ought to have/should have asked her first.
Assumptions and deductions
That will be James – he’s often early.
The book should be interesting.
There must be a leak.
You must have dialled the wrong number.
You can’t have finished already!
Can you pass me the dictionary?
Could you help me with my translation?
Will you buy me an ice cream, Mum?
Would you type this letter for me, please?
**Note: Could and would are more formal than can and will.
Offers and suggestions
Shall I do the washing-up?
Shall we go now?
I’ll take you to the airport.
*For more information about modal verbs, look at the notes at the entries for CAN, MODAL, MUST, NEED and SHOULD.
Source: Oxford Advanced Learner’s Dictionary (Eighth Edition).