May and Might: Possibility

A. May and might often have a similar meaning when we talk about possibility. However, we prefer may in academic or formal language to talk about the characteristics or behaviour of something:

1. The seeds from the plant may grow up to 20 centimetres in length.
   And in speech/spoken English, we prefer might to say what we will possibly do in the future:
2. I might paint the kitchen purple.

B. We don't use may to ask questions about the possibility of something happening. Instead we use, for example, could(n't) or the phrase be likely:

1. Could it be that you don't want to leave? (not May it be that you...)
   
2. Are you likely to be in Spain again this summer? (not May you be in Spain...?)

It is possible to use might in this type of question, but it is rather formal: 

1. Might they be persuaded to change their minds?

Note that we can use may in formally asking for permission and offering help:

1. May I leave now?
2. May I help you?

C. Might (not 'may') + bare infinitive is sometimes used to talk about what was typically the case in the past. This is a formal or literary use:

1. During the war, the police might arrest you for criticising the king.
2. Years ago children might be sent down mines at the age of six. (passive form)
   
   We can also use could + bare infinitive in examples like this to talk about past ability.
3. For example, 'During the war, the police could arrest you...' means that the police were legally able to arrest you.

D. When we say that a person or thing compensates to some extent for a limitation or weakness by having another characteristic, we can use a pattern with may/might not + bare infinitive ..but... or may/might not have + past participle...but...

1. The painting may not be a masterpiece, but you've got to admit that the colours are striking.
2. She might not have danced very gracefully, but she had a lot of energy and enthusiasm.

E. We use may/might (not 'can') + have + past participle and may/might (not 'can') + be + -ing to talk about possible events in the past, present and future:

1. Do you think Jean may/might have completed the report by now? (past)
2. His maths may/might have improved by the time the exam comes round. (future)
3. Malcolm isn't in his office. He may/might be working at home today. (present)
4. When I go to Vienna I may/might be staying with Richard, but I'm not sure yet. (future)

Note that could/can be used in the same patterns instead of may or might:
Example: Do you think Jean could have completed the report by now?

We can use may/might have been + -ing to talk about possible situations or activities that went on over a period of past time:

Example: David didn't know where the ball was, but he thought his sister might have been playing with it before she left for school.

F. We can use might/could + have + past participle to criticise someone because they didn't do something we think they should have:

Example: She's gone without us. She might/could have waited!

Try this exercise to test your grammar.

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