Could – English modal auxiliary – English Grammar in Use
We use could in a number of ways. Sometimes could is the past of can (see Unit 26):
Listen. I can hear something. (now)
I listened. I could hear something. (past)
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.
Please note that the focus of this course is: Could – English Modal Auxiliary
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)
We could go to the cinema.
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)
We also use could (not can) to say that something (a situation or a happening) is possible now or in
the future. The meaning is similar to might or may (see Unit 29):
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. (the weather now, not in general)
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 when you were in Paris? You could have stayed with Sarah.
(you didn’t stay with her)
David was lucky. He could have hurt himself when he fell, but he’s OK.
We use couldn’t to say that something 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 (done):
We had a really good holiday. It couldn’t have been better.
The trip was cancelled last week. Paul couldn’t have gone anyway because he was ill.
(= it would not have been possible for him to go)