Unit 10 Modal Verbs of Deduction May and Might

‘May’ and ‘might’ are often used to say there is a chance that something is true or that there is a possibility of it happening.

E.g. I think Labour are going to win. – You may be right.

(= It’s possible that you are right.)

Peter might phone. If he does, ask him to ring later.

In this meaning ‘might’ is not used as a past form of ‘may’: both ‘may’ and ‘might’ are used to talk about the present or future. ‘Might’ suggests a smaller chance than ‘may’, it is used when people think that something is possible but not very likely. Compare:

I may go to London tomorrow. (perhaps 50% chance)

I might go to London tomorrow. (perhaps 30% chance)

‘May’ is not normally used in direct questions about probability.

E.g. Are you likely to go camping this summer? (NOT May you go …?)

But ‘may’ is possible in negative questions about probability, which is very formal, or in indirect questions after ‘Do you think’.

E.g. May he not be making a big mistake? (very formal)

Do you think he may go camping this summer?

Note the difference between ‘may (might) not’ and ‘cannot’. ‘May (might) not’ means ‘It is possible that … not …’ while ‘cannot’ means ‘It is not possible that’.

E.g. It may (might) not be true. (= It’s possible that it is not true.)

It can’t be true. (= It is not possible that it is true.)

‘Might’ (but not ‘may’) can have a conditional meaning (=would perhaps).

E.g. If you went to bed for an hour you might feel better.

(= perhaps you would feel better.)

To say that it is possible that something happened or was true in the past, the structure ‘may/might + perfect infinitive’ is used.

E.g. Polly is very late. She may (might) have missed the train.

(It is possible that she missed the train.)

Can and Could

‘Can’ is used in questions and negative sentences to talk about the logical possibility that something is true or something is happening.

E.g. There’s the bell. Who can it be? – It can’t be your mother. She’s in Rome.

‘Can’ is not usually possible in affirmative sentences with this meaning. Instead, ‘could, may or might’ are used.

E.g. Where’s Sarah? – She could/may/might be at Joe’s place. (NOT She can be)

But ‘can’ is possible in affirmative sentences with words like ‘only, hardly’, which have a limiting or negative meaning.

E.g. Who’s that at the door? – It can only be a postman.

The structure ‘can/could’ + perfect infinitive’ is used to talk about possibility in the past.

E.g. Where can she have gone? – She can’t have gone to school. It’s Sunday.

‘Could’ can also be used to say that something was possible but did not happen (a conditional use).

E.g. That was a bad place to go skiing. You could have broken your leg.

Must

‘Must’ can be used to express the conclusion that something is certain.

E.g. You must be joking.

‘Must’ is not normally used in questions and negative clauses. ‘Can’ is used instead.

(NB. However, the form ‘That mustn’t be …’ is possible in American English.)

E.g. That lady can’t be his mother – she isn’t old enough.

There is somebody at the door. Who can it be? (NOT ‘Who must it be?’)

But in question tags ‘mustn’t’ is normal.

E.g. It must be a nice place, mustn’t it?

‘Must + perfect infinitive’ is used to express certainty about the past.

E.g. Julie is late. She must have missed the train.

Will

‘Will’ can express certainty or confidence (greater than ‘must’) about present or future situations.

E.g. Don’t phone them now. They will be having dinner.

‘Will + perfect infinitive’ can express certainty and confidence about the past.

E.g. We can’t go and see them now. They will have gone to bed.