Page 350 - Practical English Usage 3ed - Michael Swan, Oxford

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another use of may/might: typical occurrences
In scientific and academic language, may is often used to talk about typical occurrences - things that can happen in certain situations.
A female crocodile may lay 30-40 eggs.
The flowers may have five or six petals, pink or red in colour. Children o f divorced parents may have difficulty with relationships.
With this meaning, might can be used to talk about the past. III those days, a man might be hanged for stealing a sheep.
can and could are used in a similar way, but are less formal. See 122.2,4.
may and might (3): permission
May and might are used for permission mostly in a formal style. They are much less common than can and could.
asking for permission: May I put the TV on?
May and might can both be used to ask for permission. Might is very polite and formal, and is mostly used in indirect question structures.
May I put the 1V on?
1 wonder if1 might have a little more cheese.
(More natural than Might I have ...1')
giving and refusing permission: You may / You may not
May is used to give permission; may not to refuse permission or forbid. MayIputthe1Von?- Yes,ofcourseyoumay.
May I borrow the car? - No, I'm afraid you may not.
Students may not use the staffcar park.
Must not is also used to forbid (see 360.3). It is a little stronger or more emphatic than may not.
Students must not use the staffcar park.
talking about permission
We do not usually use may and might to talk about permission which has already been given or refused, about freedom which people already have, or about rules and laws. Instead, we use can, could or be allowed.
These days, children can I are allowed to do what they like. (NOT • • • children nttty ti6 ftlhar they like.)
I could I was aUowed to read what I liked when 1 was a child. (NOT i ' might f'etfti ttlhtit lliketi ...)
Can you I Are you allowed to park on both sides o f the road here? (More natural than Mayyou park...1')
indirect speech
However, may and might can be used to report the giving of permission. May is used after present reporting verbs, and might after past verbs.
The Manager says that we may leave our coats in the downstairs toilet. What are you doing here? - Peter said that I might look round. (very formal)
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