Grammar Guru — Can, could
Can выражает способность или возможность выполнить действие: могу, умею. Он используется в двух формах:
- can — в настоящем времени
- could — в прошедшем времени и сослагательном наклонении.
В отрицательных предложениях к обоим глаголам добавляется частица not:
- can — can’t
- could — couldn’t.
The verb can has some peculiarities of use:
| 1) ability (physical, mental), skills | I can run fast. She can drive well. He could read when he was four. These children can use computers well. |
| 2) request, permission | — Can I use your telephone? — Of course you can. (No, you can’t.) — Could you help me? — Of course I can. (I’m afraid I can’t.) |
| 3) objective possibility | You can always have a quick snack at McDonald’s. You can cross the street here. |
| 4) doubt, uncertainty, distrust (compare in Russian: really, it can’t be) | Can it be true? (Неужели это правда?) It can’t be true. (He может быть, что это правда.) |
| 5) reproach (you could...) | You could be more polite. (Ты мог бы быть повежливее.) She could have called us. (Она могла бы и позвонить нам, но не сделала этого.) |
Could and was able to
We use could for general ability. But if you want to say that somebody did something in a specific
situation, use was/were able to (not could):
- The fire spread through the building very quickly, but fortunately everybody was able to
escape . (not could escape) - We didn’t know where David was, but we were able to find him in the end. (not could find)
Compare:
Jack was an excellent tennis player when he was younger. He could beat anybody. (= he had the general ability to beat anybody)
but
Jack and Andy played a match yesterday. Andy played well, but Jack was able to beat him.
(= he was able to beat him this time)
The negative couldn’t (could not) is possible in all situations:
- My grandfather couldn’t swim.
- We looked for David everywhere, but we couldn't find him.
- Andy played well, but he couldn’t beat Jack.
You can say that somebody is able to do something, but can is more usual:
- We are able to see the lake from our hotel.
But can has only two forms: can (present) and could (past). So sometimes it is necessary to use (be)
able to. Compare:
- | can’t sleep.
- | haven't been able to sleep recently.
- Tom can come tomorrow.
- Tom might be able to come tomorrow.
- Maria can speak French, Spanish and English.
- Applicants for the job must be able to speak two foreign languages.
- We use could (not can) for actions that are not realistic. For example:
- I'm so tired, | could sleep for a week. (not | can sleep for a week)
Compare can and could:
- | can stay with Sarah when | go to Paris. (realistic)
- Maybe | could stay with Sarah when | go to Paris. (possible, but less sure)
- This is a wonderful place. | could stay here for ever. (unrealistic)
2. We use could (not can) to say that something (a situation or a happening) is possible now or in
the future.
- The story could be true, but | don’t think it is. (not can be true)
- | 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)
3. We use could have (done) to talk about the past. Compare:
- I'm so tired, | could sleep for a week. (now)
| was so tired, | 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.
4. We use couldn't to say that something would not be possible:
- | 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)