Sign in
Can, could, may, or might
Can is ability or permission, could is its past or softer form, and may and might mean something is possible; may is also formal permission.
Quick rule
Ability or casual permission? Can. Past ability or a polite request? Could. Formal permission or a possibility? May. A possibility with some doubt? Might.
Ability now: I can swim. Also asking for or giving permission: Can I sit here?
The past of can (I could swim at five), a possibility (it could rain), or a more polite request: Could you help me?
Something is possible (it may rain), or formal permission: May I come in?
Something is possible, often with more doubt: it might rain. It is rarely used for permission.
How to choose
| Question | can | could | may | might |
|---|---|---|---|---|
| Can it say someone is able to do something? | Yes | Yes | No | No |
| Is it the past form of one of the other three? | No | Yes | No | SometimesSometimes |
| Can it give permission (You ___ go)? | Yes | No | Yes | No |
Why it trips people up
All four can express possibility, but they don't overlap completely. Can is ability and everyday permission, could adds the past and politeness, may adds formality, and might is the most tentative. The tricky spots: can doesn't work for a future possibility, and may isn't used for requests.
How each one works
Can
Ability
She can speak three languages.
Asking permission casually
Can I use your phone?
Something that happens sometimes
It can get very cold here in winter.
Could
Ability in the past
I could ride a bike when I was four.
A polite request
Could you open the window, please?
A possibility
It could be a mistake.
May
Asking permission formally
May I ask a question?
A possibility
The flight may be delayed.
Giving permission formally
You may leave now.
Might
A possibility with doubt
I might go to the party, but I'm not sure.
Warning about something possible
Bring a sweater. It might get cold tonight.
In reported speech
She said she might be late.
What comes next
can plus verb, no to
I can help you tomorrow.
could plus verb: past of can
We could hear the music from our room.
Could you plus verb...? to ask a favor
Could you call me back?
May I plus verb...? formal permission
May I see your passport?
might plus verb: maybe
We might move to Cusco next year.
Almost the same
It can be cold in April.
It happens sometimes: a general fact.
It could be cold tomorrow.
It's possible tomorrow; can doesn't work here.
It might be cold tomorrow.
Also possible, maybe with a bit more doubt.
Can I leave early?
An everyday question.
May I leave early?
More formal, like asking a boss.
In a conversation
- A:
Can you come to my party on Saturday?
- B:
I might. I may have to work, but I'll let you know.
- A:
Could you bring some music if you come?
- B:
Sure, I can do that.
Common mistakes
Wrong: Yes, you could borrow my car this weekend.
Right: Yes, you can borrow my car this weekend.
To give permission, use can or may. Could asks for permission but does not give it.
Wrong: After three hours, we could find the hotel.
Right: After three hours, we managed to find the hotel.
For one specific success in the past, affirmative could sounds off; use managed to or were able to.
Memory trick
Line them up by confidence: can is what you know happens, could and may are possible, and might is the shyest maybe. For a favor, stick with can or could.
It depends
- May or might: which is more certain?
- Cambridge notes that native speakers disagree about which one sounds more certain. In everyday use, it may rain and it might rain are nearly the same.
- Might for permission
- Might I...? exists but is very formal and rare. For a formal request, May I...? is the usual choice.
FAQ
Can or may: which is more polite?
May is the more formal one: May I come in? Can I come in? is perfectly normal in everyday speech, and Could I...? sits in between as a safe polite choice.
Could or might for possibility?
Both work: It could rain, It might rain. Cambridge notes that native speakers disagree about which sounds more certain, so in practice they are close.