Deciding when to use can or could sometimes causes problems for English language students, especially as these words have a number of different uses.
Can or could can be used to talk about:
- Possibility / Impossibility
- Ability / no ability
- To ask for / give permission
- To give instructions / make requests
- To make offers / give invitations
Here are some tips and practice exercises to help you decide when to use can or could.
Tip 1: use can to talk about something that is possible (possibility)
- It can get very busy at the park on a Saturday afternoon.
- It can get so hot at my gym because they don’t have air-conditioning.
Tip 2: could is used as the past tense of can. (past possibility)
- It could get very busy at the park. It was so popular; I don’t know why they closed it!
- It could get so hot at my gym because they didn’t have air-conditioning. I’m glad they have installed it now.
Tip 3: could is used to show that something is possible in the future, but not certain.
- We could go to beach tomorrow evening. Let’s see what the weather is like!
- I’m going to take my cellphone with me when we go out, as James could call at anytime.
Tip 4: use can’t (cannot) to show that something is impossible (impossibility).
- She is such a nice person; I’m sure she wouldn’t do that. It can’t be true!
Tip 5: use couldn’t (could not) to show that something was impossible (past impossibility).
- Now we have all the facts we have evidence that those rumours couldn’t be true!
Tip 6: use can to talk about ability, or can’t (cannot) to talk about lack of ability
- I can sing quite well. (ability)
- I can’t (cannot) play any musical instruments. (lack of ability)
Tip 7: use could to talk about ability in the past, or couldn’t (could not) to talk about lack of ability in the past
- Mozart could play the piano when he was three years old. (ability)
- I couldn’t (could not) dance very well until I started having lessons. (lack of ability)
Tip 8: use can or could to give instructions / make requests
Note: Could is more polite than can when you are telling / asking someone to do something.
- Could you finish that as soon as you are able, please?
- Can you finish that as soon as you are able, please? (less polite – can be used when talking to someone you know well, but it is better to use could in more formal situations or when talking to people you don’t know well)
- Could you help me please?
- Can you help me please? (less polite – can be used when talking to someone you know well, but it is better to use could in more formal situations or when talking to people you don’t know well)
Tip 9: use can or could to make offers / give invitations
Note: we often use can in these situations, but could is also possible sometimes (more formal).
- Can I help you with that?
- Could I be of any assistance?
- I can drive you to work tomorrow if you need a lift.
- I could read through your report for you when you’ve finished if it would be helpful.