"May" expresses higher probability or formal permission; "might" expresses lower probability or is the past tense of "may".
Modal verb: (1) higher or moderate probability in present/future ("It may rain" = there is a reasonable possibility of rain). (2) formal permission ("You may leave now" = you have permission to leave). In formal English, it is the premier permission modal.
You may use a dictionary during the exam — it is permitted.
The package may arrive tomorrow if it was dispatched this morning.
She may be late — her train was delayed by thirty minutes.
Modal verb: (1) lower or more doubtful probability ("It might rain" = possible but less likely). (2) past tense of "may" in reported speech ("He said it might rain"). (3) tentative suggestions: "You might want to call first" = perhaps you should call first.
You might want to bring an umbrella — I saw a few dark clouds earlier.
He thought the meeting might be cancelled because the CEO was traveling.
She might come to the party, but she said she was not sure she could make it.
Common mistake
In modern colloquial English, the probability distinction between "may" and "might" is blurring and many speakers use them interchangeably. In formal and academic English, the difference matters: MAY = more probable. MIGHT = less probable. The classic error in reported speech: "She said she may come" should be "She said she might come" (past of "may" in reported speech is "might").
Trick to remember it
MAY = more probable (think of "maYbe" — there is a reasonable chance). MIGHT = less probable (think "MIGHT not happen"). For formal permission: only MAY works clearly ("May I?" = do I have permission?; "Might I?" is archaic). In reported speech: the past of MAY is always MIGHT. Direct: "I may come" becomes Reported: "He said he might come".
Quick rule
May = moderate-high probability / formal permission ("you may leave"). Might = low/doubtful probability / past of may in reported speech / tentative suggestions.
Did you know?
In 15th to 17th century English, "might" was the ordinary past tense of "may" — just as "could" is the past of "can". The probability distinction between "may" and "might" is relatively modern. Interestingly, in many American English dialects, "might could" (double modal) is perfectly acceptable in the American South: "You might could do it that way" = there is a possibility you could do it that way. This use is colloquial and dialectal, not standard.
Exercise 1 · Pick the right one
"_____ I borrow your pen for a moment?" (asking permission formally)
Exercise 2 · Pick the right one
There is a small chance of rain this afternoon, but I think it is unlikely. You _____ want to bring an umbrella just in case.
Exercise 3 · Form the word
May = moderate-high probability / formal permission ("you may leave"). Might = low/doubtful probability / past of may in reported speech / tentative suggestions.
In modern colloquial English, the probability distinction between "may" and "might" is blurring and many speakers use them interchangeably. In formal and academic English, the difference matters: MAY = more probable. MIGHT = less probable. The classic error in reported speech: "She said she may come" should be "She said she might come" (past of "may" in reported speech is "might").
MAY = more probable (think of "maYbe" — there is a reasonable chance). MIGHT = less probable (think "MIGHT not happen"). For formal permission: only MAY works clearly ("May I?" = do I have permission?; "Might I?" is archaic). In reported speech: the past of MAY is always MIGHT. Direct: "I may come" becomes Reported: "He said he might come".
Bryan López
Founder of SpeakUP Academy