Could (do) & could have(done)
A
We use could in a number of ways. Sometimes could is the past of can.( see Unit 26C)
-Listen, I can hear something.
-Listened. I could hear something.
But could is not only used in this way. We also use could to talk about possible actions now or in the future( especially to make a suggestion). For example:
A: What shall we do this evening?
B: We could go to the cinema.
-It's a nice day. We could go for a walk.
-When you go to New York next month, you could stay with Barbara.
A: If you need money, why didn't you ask Karen?
B: Yes. I suppose I could.
Can is also possible in these sentences.(' We can go for a walk' etc.). Could is less sure than can. You must use could(not can) when you don't really mean what you say. For example:
-I'm so angry with him. I could kill him! (not 'I can kill him')
B
We also use could to say that something is possible now or in the future:
-The phone is ringing. It could be Tim.
- I don't know when they'll be here. They could arrive at any time.
Can is not possible in these examples ( not’ it can be Tim’).
In these sentences, could is similar to might.
-The phone is ringing. It might be Tim.
C
Compared could ( do) and could have(done):
- I'm so tired. I could sleep for a week. (now)
- I'm so tired. I could have slept for a week. (past).
Most often, we use could have (done) for things which were possible, but did not happen:
-Why did you stay at a hotel? When you went to New York? You could have stayed with Barbara. You had the opportunity to stay with her, but you didn't.
-Jack fell off a letter yesterday, but he's all right. He's lucky. He could have hurt himself badly, but he didn't hurt himself.
-The situation was bad, but it could have been worse.
D
Sometimes could means would be able to.
-We could go away if we have enough money (= we would be able to go away)
- I don't know how you work so hard. I couldn't do it.
Could have (done) = would have been able to do:
- Why didn't Liz apply for the job? She could have got it.
-We could have gone away if we'd had enough money.
-The trip was canceled last week. Paul couldn't have gone anyway because he was ill. (= he wouldn't have been able to go)
- You did very well to pass the exam. I'm sure I couldn't have passed it.(= I wouldn't have been able to pass it if I had taken it.)
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