May

may a archaic : have the ability to b : have permission to <you may go now> : be free to <a rug on which children may sprawl — C. E. Silberman> —used nearly interchangeably with can c —used to indicate possibility or probability <you may be right> <things you may need> ; sometimes used interchangeably with can <one of those slipups that may happen from time to time — Jessica Mitford> ; sometimes used where might would be expected <you may think from a little distance that the country was solid woods — Robert Frost>

—used in auxiliary function to express a wish or desire especially in prayer, imprecation, or benediction <long may he reign> <may the best man win>

—used in auxiliary function expressing purpose or expectation <I laugh that I may not weep> or contingency <she'll do her duty come what may> or concession <he may be slow but he is thorough> or choice <the angler may catch them with a dip net, or he may cast a large, bare treble hook — Nelson Bryant>

: shall, must —used in law where the sense, purpose, or policy requires this interpretation"May" is most commonly used to express possibility. It can also be used to give or request permission, although this usage is becoming less common.

Examples:

Cheryl may be at home, or perhaps at work. possibility
Johnny, you may leave the table when you have finished your dinner. give permission
May I use your bathroom? request permission

Using "May" in Present, Past, and Future

Most modal verbs behave quite irregularly in the past and the future. Study the chart below to learn how "may" behaves in different contexts.

Modal Use	Positive Forms 1. = Present 2. = Past 3. = Future	Negative Forms 1. = Present 2. = Past 3. = Future	You can also use:
may possibility	1. Jack may be upset. I can't really tell if he is annoyed or tired. 2. Jack may have been upset. I couldn't really tell if he was annoyed or tired. 3. Jack may get upset if you don't tell him the truth.	1. Jack may not be upset. Perhaps he is tired. 2. Jack may not have been upset. Perhaps he was tired. 3. Jack may not get upset, even if you tell him the truth	might
may give permission	1. You may leave the table now that you're finished with your dinner. 2. SHIFT TO "BE ALLOWED TO" You were allowed to leave the table after you finished your dinner. 3. You may leave the table when you finish your dinner.	1. You may not leave the table. You're not finished with your dinner yet. 2. SHIFT TO "BE ALLOWED TO" You were not allowed to leave the table because you hadn't finished your dinner. 3. You may not leave the table until you are finished with your dinner.	can
may request permission	May I borrow your eraser? May I make a phone call? Requests usually refer to the near future.	NO NEGATIVE FORMS	can, might