We use may:
Jack may be coming to see us tomorrow.
(= Perhaps Jack will come to see us tomorrow.)
Oh dear! It's half past ten. We may be late for the meeting.
(= Perhaps we will be late for the meeting.)
She's had no sleep. She may be tired.
(= Perhaps she is tired.)
- to ask for permission in a formal way:
May I borrow the car tomorrow?
May we come a bit later?
- to give permission in a formal way:
You may go now.
You may come at eleven if you wish.
- to say that someone has permission in a formal way:
Students may travel for free.
We can use may not to refuse permission or to say that someone does not have permission, but it is formal and emphatic:
You may not borrow the car until you can be more careful with it!
Students may not wear jeans.
We use might when we are not sure about something in the present or future:
I might see you tomorrow.
It looks nice, but it might be very expensive.
It's quite bright. It might not rain today.
We use may have and might have to make guesses about the past:
I haven't received your letter. It may have got lost in the post.
It's ten o'clock. They might have arrived by now.
We also use might:
- as the past tense of requests with may:
He asked if he might borrow the car.
They wanted to know if they might come later.
- as a very polite way of asking for permission:
Might we ask you a question?
Might I just interrupt for a moment?
Questions and negatives
We make questions by putting the subject after may/might:
May I …? Might I …?
The negative forms are may not and might not.