UNIT 26. Could (do) and could have (done)

A

We use could in a number of ways. Sometimes could is the past of can:

Listen. I can hear something. (now)
I listened. I could hear something. (past)

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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 suggestions).
For example:

A : What would you like to do tonight?
B : We could go to the movies.

A : When you go to New York next month, you could stay with Candice.
B : Yes, I guess I could.

Can is also possible in these sentences (We can go to the movies, etc.).
Could is less sure than can.

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B

We also use could (not can) for actions which 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 Candice when I go to New York. (realistic)
Maybe I could stay with Candice when I go to New York. (possible, but less sure)
This is a wonderful place. I could stay here forever. (unrealistic)

C

We also use could (not can) to say that something is possible now or in the future.
The meaning is similar to might or may:

The story could be true, but I don’t think it is. (not can be true)
I don’t know what time Liz is coming. She could get here at tny time.

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 when you were in New York? You could have stayed with Candice. (you didn’t stay with her)
I didn’t know that you wanted to go to the concert. I could have gotten you a free ticket. (I didn’t get you a ticket)
Dave was lucky. He could have hurt himself when he fell, but he’s OK.

E

We use couldn’t to say that something would not be possible now:

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 vacation. It couldn’t have been better.
The trip was canceled last week. Paul couldn’t have gone anyway because he was sick. (= it would not have been possible for him to go)