Page 66 - English Grammar in Use

Unit
27 could (do) and could have (done)

A Sometimes could is the past of can (see Unit 26):
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:
What shall we We could go to the cinema.
a: What shall we do tonight? 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)

C We also use could (not can) to say that something is possible now or in the future:
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)

D We use could have (done) to talk about the past. Compare:
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.

E I couldn’t do something = it would not be possible:
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)

can and could ➜ Unit 26 couldn’t have (done) ➜ Unit 28B could and might ➜ Unit 29C
54 could I/you … ? ➜ Unit 37 could with if ➜ Units 38C, 39E, 40D Modal verbs (can/will etc.) ➜ Appendix 4