We use can to say that something is possible or that somebody has the ability to do something.
* We use can + infinitive (can do/can see etc.):
* We can see the lake from our bedroom window.
* Can you speak any foreign languages?
* I can come and see you tomorrow if you like.
The negative is can't (= cannot):
* I'm afraid I can't come to the party on Friday.
(Be) able to ... is possible instead of can, but can is more usual:
* Are you able to speak any foreign languages?
But can has only two forms, can (present) and could (past). So sometimes it is necessary to use (be) able to...
Compare:
* I can't sleep.
but I haven't been able to sleep recently. (can has no present perfect)
* Tom can come tomorrow.
but Tom might be able to come tomorrow. (can has no infinitive)
Could and was able to...
Sometimes could is the past of can. We use could especially with:
see hear smell taste feel remember understand
* When we went into the house, we could smell burning.
* She spoke in a very low voice, but I could understand what she said.
We also use could to say that somebody had the general ability or permission to do something:
* My grandfather could speak five languages.
* We were completely free. We could do what we wanted. (= we were allowed to do ...)
We use could for general ability. But if we are talking about what happened in a particular situation, we use was/were able to... or managed to... (not could):
* The fire spread through the building quickly but everybody was able to escape.
or ... everybody managed to escape. (but not 'could escape')
* They didn't want to come with us at first but we managed to persuade them.
or ... we were able to persuade them. (but not 'could persuade')
Compare:
* Jack was an excellent tennis player. He could beat anybody. he had the general ability to beat anybody) but
* Jack and Alf had a game of tennis yesterday. Alf played very well but in the end Jack managed to beat him. or ... was able to beat him. (= he managed to beat him in this particular game). The negative couldn't (could not) is possible in all situations:
* My grandfather couldn't (could not) is possible in all situations
* We tried hard but we couldn't persuade them to come with us.
* Alf played well but he couldn't beat Jack.
EXERCISES
26.1 Complete the sentences using can or (be) able to. Use can if possible; otherwise use (be) able to.
1. George has travelled a lot. He _can_ speak four languages.
2. I haven't _been able to_ sleep very well recently.
3. Sandra --- drive but she hasn't got a car.
4. I can't understand Martin. I've never --- understand him.
5. I used to --- stand on my head but I can't do it now.
6. I can't see you on Friday but I --- meet you on Saturday morning.
7. Ask Catherine about your problem. She might --- help you.
26.2 Write sentences about yourself using the ideas in brackets.
1. (something you used to be able to do) I used to be able to sing well.
2. (something you used to be able to do) I used ---
3. (something you would like to be able to do) I'd ---
4. (something you have never been able to do) I've ---
26.3 Complete the sentences with can/can't/could/couldn't + one of these verbs:
come cat hear run sleep wait
1. I'm afraid I _can't come_ to your party next week.
2. When Tim was 16, he was a fast runner. He --- 100 meters in 11 seconds.
3. Are you in a hurry?' 'No, I've got plenty of time. I ---.'
4. I was feeling sick yesterday. I --- anything.
5. Can you speak up a bit? I --- you very well.
6. 'You look tired.' 'Yes, I --- last night,'
26.4 Complete the answers to the questions with was/were able to.
1 A: Did everybody escape from the fire?
B: Yes. Although the fire spread quickly, everybody _was able to escape._
2 A: Did you have difficulty finding Ann's house?
B: Not really. Ann had given us good directions and we ---
3.A: Did you finish your work this afternoon?
B: Yes. There was nobody to disturb me, so ---
4. A: Did the thief get away?
B: Yes. No one realised what was happening and the thief ---
26.5 Complete the sentences using could, couldn't or was/were able to.
1. My grandfather was a very clever man. He _could_ speak five languages.
2. I looked everywhere for the book but I _couldn't_ find it.
3. They didn't want to come with us at first but we _were able to_ persuade them.
4. Laura had hurt her leg and --- walk very well.
5. Sue wasn't at home when I phoned but I --- contact her at her office.
6. I looked very carefully and I --- see a figure in the distance.
7. I wanted to buy some tomatoes. The first shop I went to didn't have any but I --- get some in the next shop.
8. My grandmother loved music. She --- play the piano very well.
9. A girl fell into the river but fortunately we --- rescue her.
10. I had forgotten to bring my camera so I --- take any photographs.
26.1
3 can
4 been able to
5 be able to
6 can
7 be able to
26.2 Example answers:
2 I used to be able to run fast.
3 I'd like to be able to play a musical instrument.
4 I've never been able to get up early.
26.3
2 could run
3 can wait
4 couldn't eat
5 can't hear
6 couldn't sleep
26.4
2 were able to find it.
3 I was able to finish it.
4 was able to get away.
26.5
4 couldn't/wasn't able to
5 was able to
6 could/was able to
7 was able to
8 could/was able to
9 were able to
10 couldn't/wasn't able to
