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"May" and "might" are modal verbs that express possibility, probability, and permission. While they are often used interchangeably for possibility, there are subtle differences in probability level, formality, and grammatical behavior that every English learner should understand. "May" also serves as a formal way to grant or request permission — a function that "might" rarely fills in modern English. This comprehensive guide explores every use of "may" and "might," their differences, and common pitfalls to avoid.
Table of Contents
May and Might for Possibility
Both "may" and "might" express that something is possible — that there is a chance it could happen or be true. In most everyday contexts, they are interchangeable for this meaning.
It may rain this afternoon. / It might rain this afternoon.
She may be at home. / She might be at home.
We may go to Spain this summer. / We might go to Spain this summer.
The store may be closed on Sundays. / The store might be closed on Sundays.
In these examples, there is no significant difference in meaning. Both express uncertainty about the situation — the speaker does not know for sure and is acknowledging that the event is possible but not certain.
Degrees of Probability
Some grammarians and style guides suggest that "may" expresses a slightly higher probability than "might." According to this view, "may" means something is reasonably likely, while "might" suggests something is less likely or more hypothetical. However, this distinction is not consistently observed by all native speakers, and in everyday conversation, the two are largely interchangeable.
| Modal | Approximate Probability | Example |
|---|---|---|
| will | ~95-100% certain | It will rain tomorrow. (I'm sure.) |
| should / ought to | ~80-90% expected | It should rain tomorrow. (I expect it.) |
| may | ~40-60% possible | It may rain tomorrow. (It's possible.) |
| might / could | ~20-40% possible | It might rain tomorrow. (There's a chance.) |
Practical Advice: In everyday English, don't worry too much about the probability difference between "may" and "might." Both work perfectly for expressing possibility. The more important distinctions are: (1) "may" is used for formal permission while "might" is not, and (2) "might" is preferred in hypothetical/unreal situations.
May for Permission
"May" is the traditional, formal way to ask for and grant permission in English. It is more polite and formal than "can" and is often associated with polite speech, classroom language, and formal writing.
Asking Permission
May I come in? (very polite/formal)
May I ask a question? (polite — common in classrooms)
May I use your telephone? (polite)
May I have another cup of coffee? (polite request)
Granting and Denying Permission
You may leave the room. (formal permission granted)
Students may use dictionaries during the test. (allowed)
You may not use your phone during the exam. (formal prohibition)
"Might" for Permission? While "might" was historically used for permission (as the past tense of "may"), this use is extremely rare in modern English. "Might I borrow your pen?" sounds very old-fashioned and overly formal. In practice, use "may" for formal permission and "can" for informal permission.
May Have / Might Have (Past Possibility)
To express possibility about a past event — something that perhaps happened but you are not sure — use "may have" or "might have" followed by a past participle.
She may have missed the bus. (It's possible she missed it.)
He might have forgotten about the meeting. (Perhaps he forgot.)
They may have already left. (It's possible they're gone.)
The letter might have been lost in the mail.
Might Have in Unreal Conditionals
In third conditional (unreal past) situations, "might have" is preferred over "may have" because the situation is hypothetical, not just uncertain.
If you had reminded me, I might have remembered. (hypothetical — "may have" is less natural here)
If she had applied, she might have gotten the job.
Negatives: May Not vs Might Not
"May not" and "might not" both express the possibility that something will not happen or is not true. Unlike "must not" (prohibition) and "can't" (impossibility), "may not" and "might not" express uncertainty in the negative direction.
She may not come to the party. (Perhaps she won't come.)
He might not pass the exam. (There's a chance he'll fail.)
We may not have enough time. (It's possible we don't.)
The plan might not work. (It could fail.)
Contraction Note: "May not" is never contracted to "mayn't" in modern English. "Might not" can be contracted to "mightn't" in British English, though it is not very common. In American English, the full form "might not" is standard.
Formal Uses of May
"May" has several formal uses that "might" does not share. These are common in written English, official documents, speeches, and academic writing.
Wishes and Blessings
May you have a wonderful birthday!
May God bless you.
May the best team win.
May your dreams come true.
Formal Writing (Concessive Clauses)
The theory may be controversial, but it has strong evidence to support it.
While the results may seem surprising, they are consistent with previous studies.
Side-by-Side Comparison
| Feature | May | Might |
|---|---|---|
| Possibility | Yes — slightly higher probability | Yes — slightly lower probability |
| Permission | Yes — formal | Extremely rare (old-fashioned) |
| Formal wishes | Yes: "May you be happy" | No |
| Hypothetical situations | Less natural | Preferred: "If I tried, I might succeed" |
| Past possibility | may have + V3 | might have + V3 |
| Formality level | More formal | Slightly less formal |
| Contraction | No contraction | mightn't (rare, British) |
Common Mistakes to Avoid
Mistake 1: Using "May" in Conditional Sentences
Unnatural: If I studied harder, I may pass.
Better: If I studied harder, I might pass. (hypothetical → "might")
Mistake 2: Confusing "May Not" (Possibility) with "Must Not" (Prohibition)
"May not" = possibly won't: She may not come. (Maybe she won't.)
"Must not" = it is forbidden: You must not enter. (It's prohibited.)
Mistake 3: Using "Might" for Formal Permission
Old-fashioned: Might I leave early today?
Natural: May I leave early today? / Could I leave early today?
Mistake 4: Writing "May of" or "Might of"
Incorrect: She might of been late.
Correct: She might have been late.
Practice Exercises
Exercise 1: May, Might, or May/Might Have?
1. ___ I sit here? (formal permission)
2. It ___ snow tonight — check the forecast. (possibility)
3. If we had left earlier, we ___ ___ avoided the traffic. (unreal past)
4. She's not answering. She ___ ___ gone to bed already. (past possibility)
5. ___ all your wishes come true! (formal blessing)
Answers
1. May I sit here?
2. It may / might snow tonight.
3. If we had left earlier, we might have avoided the traffic.
4. She may / might have gone to bed already.
5. May all your wishes come true!
Summary
"May" and "might" are essential modal verbs for expressing possibility and uncertainty in English. While they are largely interchangeable for general possibility, "may" carries slightly higher probability and is the standard choice for formal permission and wishes. "Might" is preferred in hypothetical or unreal situations. Both can combine with "have + past participle" to discuss past possibilities. Understanding these distinctions — and especially the difference between "may not" (possibility) and "must not" (prohibition) — will help you communicate with precision, politeness, and sophistication in every English context.
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