may, might

May and might are helping verbs that can express possibility or permission.

• I may (or might) go to the conference with Johanne tomorrow.
• May I have some more cake?
• Yes, you may have some more cake.

Some authorities believe there is a difference between the two forms when they are used to express possibility, with may conveying possibility and might, unlikely possibility.

• She may have been in the office when we telephoned, or she might have been in Tuktoyaktuk, for all I know.

It is important to note that may expresses possibility in the present; might must be used when the possibility of doing something existed only in the past:

• Johnson may have survived; we are waiting for news.
  [There is a possibility that he survived; we don’t know yet.]
• Johnson’s death last week might (not may) have been prevented if the ambulance had responded more rapidly.
  [There was a possibility in the past of preventing his death; but since he died, that possibility no longer exists.]

Might is sometimes preferred when you are asking for permission and more politeness or formality is required.

• Might I ask a question, Sir?