Learn and practise the use of could (do) and could have (done).A Sometimes could is the past of can:
- Listen. I can hear something. (now)
- I listened. I could hear something. (past)
But could is not always past. We also use could for possible actions now or in the future, especially to make suggestions. For example:
a: What shall we do tonight?
b: We could go to the cinema.
a: When you go to Paris next month, you could stay with Sarah.
b: Yes, I suppose I could.
Can is also possible in these sentences (‘We can go to the cinema.’ etc.). Could is less sure than can.B We also use could (not can) for actions that are not realistic. For example:
- I’m so tired, I could sleep for a week. (not I can sleep for a week)
Compare can and could:
- I can stay with Sarah when I go to Paris. (realistic)
- Maybe I could stay with Sarah when I go to Paris. (possible, but less sure)
- This is a wonderful place. I could stay here for ever. (unrealistic)
- The story could be true, but I don’t think it is. (not can be true)
- I don’t know what time Lisa is coming. She could get here at any time.
Compare can and could:
- The weather can change very quickly in the mountains. (in general)
- The weather is nice now, but it could change later. (the weather now, not in general)
- I’m so tired, I could sleep for a week. (now)
- I was so tired, I could have slept for a week. (past)
- The situation is bad, but it could be worse. (now)
- The situation was bad, but it could have been worse. (past)
Something could have happened = it was possible, but did not happen:
- Why did you stay at a hotel? You could have stayed with me. David was lucky. He could have hurt himself when he fell, but he’s all right.
- I couldn’t live in a big city. I’d hate it. (= it wouldn’t be possible for me)
- Everything is fine right now. Things couldn’t be better.
For the past we use couldn’t have … (= would not have been possible):
- We had a really good holiday. It couldn’t have been better.
Note that ‘I couldn’t do something’ has two meanings:
(1) I couldn’t = it would not be possible now, I would not be able:
- I couldn’t run ten kilometres now. I’m not fit enough. (= I would not be able)
(2) I couldn’t = I was not able (past)
- I couldn’t run yesterday because I’d hurt my leg. (= I was not able)