Use can for ability now and could for general ability in the past: I can swim. I could swim when I was five. For one particular success in the past, use was able to or managed to: I was able to fix it. For permission and requests, can is casual, could is polite and may is formal: Could I ask a question?
Could I ask you a question?
Asking for permission has its own gauge: can is casual, could is polite and may is formal.
| can | Ability now; casual permission: I can drive. Can I sit here? |
|---|---|
| could | General ability in the past; polite requests: She could read at four. Could you help me? |
| was / were able to | One particular success in the past: We were able to finish on time. |
| will be able to | Ability in the future: You'll be able to speak French by June. |
| may | Formal permission: May I come in? |
Can has no future or perfect form. Use be able to: I'll be able to help tomorrow. I've never been able to whistle.
She can speak three languages.
What someone is able to do at present.
I could swim when I was five.
Something you were able to do in general, over a period of time.
The exam was hard, but I was able to finish it.
For one specific occasion, use was able to or managed to, not could.
Could you open the window, please?
Can is casual, could is polite, may is formal (and only for asking permission: May I…?).
Common expressions worth learning as they are.
Next year I _____ drive.
How sure, how necessary, how polite.
Paste an email or an essay. Clarigram marks the mistakes you actually make, shows the rule behind each one as a picture, and builds your practice from them.
Yes. In the negative, couldn't works for one occasion too: I tried, but I couldn't open the door.
Both are correct. Can is normal in everyday English; may is more formal and polite.