What is the difference between may, might, and could?

As possibility markers they overlap. May is a little more formal (The crossing may still run), might is often a shade more tentative (She might still be in the wings), and could as a guess sits close to might (That could be the harbour master). None of the three names a different fact; they name a different tone. Could also has ability and permission readings that may and might do not share in the same way.

Is could only used for ability?

No. Could is ability in She could already read music at six, and it is a polite request in Could I leave the cello. It is also a present or future possibility: That could be Maya. We could try the later crossing. If you can swap could for might and keep the meaning, you have possibility. If you can swap it for was able to, you have ability.

Do may, might, and could mean the same thing for the future?

Often yes. It may drizzle, It might drizzle, and It could drizzle are all legal guesses about later weather. Choose may for a careful written prediction, might if you want to sound less sure, and could if you are listing an option. If you are almost certain, none of the three is strong enough: use will, should, or be likely to, which belong on the future-probability page.

How do I talk about past possibility with these verbs?

Add have plus a past participle: She may have missed the cue. She might have gone to the annex. She could have left with the trustee. The modal itself does not go into the past (not she might had gone). Couldn't have means that past does not fit the evidence: She couldn't have taken the key; it's still on the hook.

When should I choose could instead of may or might?

Choose could when you are guessing an identity or a cause (That could be the stage manager. The delay could be the tide gate) or when you are offering an option (We could wait for the dawn ferry). Choose may when the register is formal. Choose might when you want the guess to sound tentative, or when you are reporting past may: She said she might be late. In many spoken guesses, any of the three will pass.

English grammar · Intermediate

May, Might, and Could: Three Degrees of Possibility

Written by Eleanor Whitfield, Lead English Curriculum Editor · Reviewed September 2026

May, might, and could all mark possibility: a guess about now, later, or (with have plus a participle) the past. May is the most formal and often the most real-sounding chance. Might can sound slightly remoter or more tentative. Could as possibility, not ability, sits close to might (That could be the stage manager). The three overlap a great deal; the useful work is hearing could as a guess, not only as past or present ability.

The crossing may still run; it might wait for the tide, or that could be the harbour master on the radio.

three-way present possibility: may, might, and could as a guess

What it is

English has several ways to say I am not sure. May, might, and could are the three light-to-mid guesses. They all take a bare verb (may berth, might wait, could be) and they all refuse do. May is slightly more formal and can still sound like a real option (We may berth tonight). Might often sounds a shade less likely or more polite (We might have to wait for the next tide). Could in this meaning is a guess, not a skill: That could be the harbour master does not ask whether he is able to be the harbour master. Ability could (She could already read music at six) and permission could (Could I leave the cello in the office?) are different jobs and belong on the wider could page. Must and can't as deduction belong on the possibility-modals page; this one stays with the three-way overlap.

She may still be in the wings. She might have gone to the annex. That could be her headset on the hook. (Three guesses, three distances, none of them ability.)

How to spot it

Look for may, might, or could plus a base verb, with the meaning I am not certain. If could means was able to or would be able to, you have left this page. If the sentence grants or requests permission (May I, Could I), that is permission, not possibility, though the same words are used.

The crossing may still run after midnight. (may: a real present chance, slightly formal)
She might still be in the wings. (might: a slightly more tentative guess)
That could be the stage manager on the stairs. (could as identity-guess, not ability)
We could try the later crossing if this one is cancelled. (could as a possible option)

May not and might not mean it is possible that something will not happen. Could not in the present usually sounds like ability (She couldn't lift the harp), so for a negative guess prefer may not, might not, or couldn't have for the past.

May, Might, and Could Quick Reference

The three-way possibility set

Modal	Typical flavour	Example
may	real chance, slightly formal; also permission	The preview may overrun.
might	slightly remoter or more tentative; past of may in reports	The preview might overrun.
could	possibility or option; also ability and polite requests	The preview could overrun. That could be Maya.
may / might / could have + participle	a guess about the past	She may have left. She might have left. She could have left.
may not / might not	possible that it is not true / will not happen	She might not have heard the cue.
couldn't have	past guess that something was impossible, or that a chance was missed	She couldn't have heard the cue; the tannoy was down.

Common May, Might, and Could Examples in English

Possibility in three flavours, then the overlap that makes choosing among may, might, and could a matter of tone more than of truth:

Guesses about Now and Later

The crossing may still run; the radio has not closed the harbour.: may: a live option
She might still be in the wings, waiting for the encore cue.: might: a softer present guess
It may drizzle before the quarry path dries.: may about a later stretch of time
They might postpone the preview if the kiln is still firing.: might about a future decision

In modern speech, It may rain and It might rain are often the same guess. Might can feel a little less committed; it does not name a different weather system.

Could as Possibility, Not Ability

That could be the harbour master on the radio.: identity guess
The delay could be a problem with the tide gate.: cause guess
We could try the later crossing if this one fills.: option, not a claim of skill
He could be waiting in the annex; the foyer is dark.: present location guess

Swap could for might in these sentences and the meaning barely moves. Swap it for was able to and the meaning collapses. That test tells you you are on the possibility reading.

Past Guesses with Have

She may have missed the cue; the tannoy was faint.: may have: a past possibility still on the table
She might have gone to the annex for the spare mute.: might have: slightly more tentative past guess
She could have left with the trustee; I didn't see her leave.: could have: one possible past
She couldn't have taken the spare key; it's still on the hook.: couldn't have: that past is not possible

Could have also means a missed opportunity (You could have texted). Possibility and missed chance share a form; the rest of the sentence tells you which one you have.

Where the Three Overlap

Maya may be the one who locked the annex.: may: a candidate, slightly formal
Maya might be the one who locked the annex.: might: same candidate, softer
Maya could be the one who locked the annex.: could: same candidate, spoken guess
The later crossing may / might / could still have seats.: all three legal; tone, not truth, changes

Do not spend exam time hunting a hidden difference of fact among these three. Spend it checking that could is not being read as ability, and that must / can't have not slipped in from a stronger deduction.

How May, Might, and Could Work as Possibility

One pattern, three flavours, and a past built with have plus a participle.

Modal plus Bare Verb, No Do

May, might, and could are true modals in this use. They do not take -s, to, or do: She may wait, not she mays wait, not she may to wait, not does she may wait. The question inverts the modal: Might she still be in the wings? Could that be the harbour master?

Might she still be in the wings? Could that be her headset?

modal in front of the subject, base verb after

Modal + base verb. No do.

May, Might, and Could Overlap for Guesses

For a present or future chance, all three are often possible. May is the more formal or more real-sounding option. Might adds tentativeness or, in reports, serves as the past of may (She said she might be late). Could as a guess sits closest to might. The dedicated may vs might page drills that pair; here the third member is the point.

The preview may overrun. It might overrun. It could overrun.

three legal guesses, rising informality

Same guess; different tone.

Could Means Possibility When Ability Does Not Fit

If the sentence is about identity, cause, or whether an event will happen, could is a possibility modal: That could be Maya. The delay could be the tide gate. If the sentence is about skill or past ability, could is not this page: She could already read a full score at six. Context, not the word itself, chooses the reading.

That could be the stage manager. She could lift the harp when she had to.

first sentence: guess; second: ability

If was able to fits, it is ability.

Past Possibility Adds Have plus a Participle

May have, might have, and could have plus a past participle guess about a finished event. The modal stays in the present form; have never becomes had after it. Couldn't have often means that past was impossible. Could have without not can still be a missed chance: You could have texted the berth number.

She might have gone to the annex. She couldn't have taken the key; it's on the hook.

open past guess vs closed-off past

Modal + have + participle for past guesses.

Common Mistakes with May, Might, and Could

Incorrect: That can be the harbour master, but I'm not sure.

Correct: That could be the harbour master, but I'm not sure.

Can for present possibility is limited in statements about identity (It can be cold here in March is a general truth, not a guess). A specific guess wants could, might, or may. I'm not sure is the clue that you are not stating a general fact.

Incorrect: She mays still be in the wings.

Correct: She may still be in the wings.

May, might, and could stay the same after she, he, or it. There is no mays or mights, and the verb after them stays bare: she may be late, not she mays be late.

Incorrect: She could have gone to the annex, so she was able to gone.

Correct: She could have gone to the annex.

Could have gone is already the past guess. Was able to gone mixes ability grammar with the wrong verb form. If you mean ability, She was able to go. If you mean a guess, keep could have gone and stop.

Incorrect: He might of missed the cue.

Correct: He might have missed the cue.

The reduction might've sounds like might of, but the word is have. The same spelling trap catches could of and may of. Write have every time.

Could as Possibility, and the Have Forms

The reading learners miss, and the past pattern that all three modals share.

Tests that tell possibility from ability

Replace could with might. If the sentence still works, you have possibility. Replace it with was able to. If that works, you have ability. Both readings can appear in one paragraph; they do not appear in one slot.

The later crossing could still have seats.: might still have seats: possibility
At sixteen she could already tune a harp.: was able to tune: ability
We could wait for the dawn ferry if this one fills.: we might wait: an option

Could I leave the cello is permission, a third reading. Possibility questions more often start with could that / could it: Could that be Maya?

May have, might have, could have

These guess about the past. The next word is have, then a participle, never had. Negatives: may not have, might not have, could not have (couldn't have).

He may have taken the dawn ferry.: open past possibility
He might not have seen the notice on the annex door.: possible that he did not
He couldn't have seen it; the door was still locked at six.: that past is ruled out

Could of, might of, and may of are the spoken reduction of have, wrongly spelled. Always write have.

Permission is a side door, not this page's centre

May I is still the formal request. Could I is the everyday polite request. Might I is rare and very formal. Those uses share the words, not the possibility meaning.

May I leave the cello behind the desk?: formal permission
Could I leave the cello behind the desk?: polite everyday request
The cello may already be behind the desk.: possibility, not a request

A question mark and I after the modal usually mean permission. A statement about a third person or a thing usually means possibility.

Quick Check: May, Might, and Could

Choose may, might, or could (plus have where needed) so the sentence is a possibility, not ability.

1. That ___ be the stage manager; I can see a headset.

Answer: could / might / may

identity guess; all three are possible, could is the most spoken

2. The crossing ___ still run after midnight.

Answer: may / might / could

future chance; may is slightly more formal

3. She ___ still be in the wings; the encore hasn't started.

Answer: might / may / could

present location guess

4. She ___ (miss) the cue; the tannoy was faint. (past guess)

Answer: may have missed / might have missed / could have missed

modal + have + participle

5. She ___ taken the spare key; it's still on the hook. (impossible past)

Answer: couldn't have / could not have

couldn't have rules that past out

May, Might, and Could FAQs

What is the difference between may, might, and could?: As possibility markers they overlap. May is a little more formal (The crossing may still run), might is often a shade more tentative (She might still be in the wings), and could as a guess sits close to might (That could be the harbour master). None of the three names a different fact; they name a different tone. Could also has ability and permission readings that may and might do not share in the same way.
Is could only used for ability?: No. Could is ability in She could already read music at six, and it is a polite request in Could I leave the cello. It is also a present or future possibility: That could be Maya. We could try the later crossing. If you can swap could for might and keep the meaning, you have possibility. If you can swap it for was able to, you have ability.
Do may, might, and could mean the same thing for the future?: Often yes. It may drizzle, It might drizzle, and It could drizzle are all legal guesses about later weather. Choose may for a careful written prediction, might if you want to sound less sure, and could if you are listing an option. If you are almost certain, none of the three is strong enough: use will, should, or be likely to, which belong on the future-probability page.
How do I talk about past possibility with these verbs?: Add have plus a past participle: She may have missed the cue. She might have gone to the annex. She could have left with the trustee. The modal itself does not go into the past (not she might had gone). Couldn't have means that past does not fit the evidence: She couldn't have taken the key; it's still on the hook.
When should I choose could instead of may or might?: Choose could when you are guessing an identity or a cause (That could be the stage manager. The delay could be the tide gate) or when you are offering an option (We could wait for the dawn ferry). Choose may when the register is formal. Choose might when you want the guess to sound tentative, or when you are reporting past may: She said she might be late. In many spoken guesses, any of the three will pass.