May vs Might: Possibility, Permission and a Small Difference

May and might are the pair learners worry about most and need to worry about least, at least for possibility, where they overlap almost completely. The real thing to know is small: there is a slight, unreliable difference in certainty, and one clear split where may does a job might cannot. Get those two points and you can stop agonising over the choice.

Possibility: nearly interchangeable

For talking about what is possible, may and might usually swap freely.

• It may rain this afternoon.
• It might rain this afternoon.
• She may know the answer.
• She might know the answer.

Both are correct and both are natural. If you are unsure which to pick for a possibility, either one is a safe choice.

The small certainty difference

Many speakers feel that might points to a slightly smaller chance than may. It is a tendency, not a rule, and not everyone follows it.

• I may go to the party. (an open possibility)
• I might go to the party. (perhaps a little less likely)

Do not lose sleep over this. Listeners rarely read much into it, and you will be understood whichever you choose. It is worth knowing the tendency exists, but not worth second-guessing every sentence.

Permission: only may

The one clear difference is permission. May asks for or grants it; might does not.

• May I come in?
• You may leave when you are ready.

Here might would sound wrong. This permission use is more formal than can, which does the same job casually, so may suits polite or official settings. If your sentence is about being allowed to do something, may is the word.

Quick guide

Ask what you mean. Possibility? Either may or might works, with might perhaps hinting at a slightly smaller chance. Permission, especially in formal or polite English? Only may. One sentence holds both jobs of may: "You may go now, though it may rain on the way."

Fine distinctions between modal verbs are the kind of detail that separates comfortable English from careful English. The pair can vs could raises the same kind of modal subtlety. A free English level test will show you whether shades like this are already second nature to you.