English speakers use some special expressions to ask for permission. These are usually constructed with may and might. Note that might is very polite and formal. It is not very common and is mostly used in indirect questions.
- May I put the heating on?
- May I have a look at your papers?
- I wonder if I might have a little more cake. (Very formal; more natural than ‘Might I have a little more cake?’)
In an informal style can and could are used.
- Can I borrow your car? (Less formal than ‘May I borrow your car?’)
- Can I go to the pictures, mom?
Giving and refusing permission
May is used to give permission; may not is used to refuse permission. These are rather formal. In an informal style can and cannot/can’t are used.
- May I come in, Sir. Yes, you may.
- May I borrow your car? No, I am afraid you may not. (More formal than ‘No, you can’t.’)
Must not is used to prohibit. It is more emphatic than may not.
- You must not smoke in the kitchen.