Page 349 - Practical English Usage 3ed - Michael Swan, Oxford

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She may be at home. (= Perhaps she is at home.)
She may not be at home. (= Perhaps she is not at home.) She can't be at home. (= She is certainly not at home.)
You might win. (= Perhaps you will win.)
You might not win. (= Perhaps you won't win.) You can't win. (= You certainly won't win.)
may and might (2): chances etc 339
4 two negatives: may/might not and can't
There are two ways to make may/might negative: with may/might not (= It is possible that ... not ...) and with can't (= It is not possible that ...) Compare:
5 might meaning 'would perhaps'
Might (but not may) can have a conditional meaning (= would perhaps). Ifyou went to bed for an hour, you mightfeel better.
(= ... perhaps you would feel better.)
Don't play with knives. You might get hurt. (= Perhaps you would get hurt.)
6 indirect speech: might
Might is used in past indirect speech when may was used in direct speech.
I may go to Scotland. - What? -1 said I might go to Scotland.
7 past: might + infinitive not used
Might + infinitive is not normally used to talk about past possibility (except in indirect speech).
I felt very hot and tired. Perhaps 1 was ill. (NOT ••• { might be ill.)
8 may/might have . ..: She may have missed her train
However, to say that it is possible that something happened or was true in the past, we can use may/might have + past participle.
Polly's very late. '" She may have missed her train. (= It is possible that she missed ...J
What was that noise? - It might have been a cat.
May/might have ... can sometimes refer to the present or future.
I'll try phoning him, but he may have gone out by now. By the end of this year I might have saved some money.
9 might have . ..: You might have killed yourself
To say that something was possible but did not happen, we can use
might have ...
You were stupid to try climbing up there. You might have killed yourself.
Ifshe hadn't been so bad-tempered, I might have married her.
May have . .. is now sometimes used with this meaning too; some people feel that this is not correct.
You were stupid to try climbing up there. You may have killed yourself. (More normal: ... You might have killed yourself.)
For mighr have . .. used to criticise people for not doing things, see 344. For the use of could have + past participle in similar senses, see 124.7.
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