We use can to say that something is possible or that someone has the ability to do something. The negative is can't (cannot). Let's see the following examples :
- You can see the sea from our bedroom window.
- Can you speak Spanish ?
- I'm afraid I can't come your party tomorrow.
"Be Able To" Can Replace "Can"
- Are you able to speak Spanish?
- I'm not able to see the sea from your bedroom window.
Present Perfect and Past Form of "Can" and "Be Able To"Because can has only two forms : can (present) and could (past), and has no present perfect, you have to use be able to in the present perfect form. Also, can has no infinitive. Let's see the following examples :
- I haven't been able to create any songs recently.
- I will not be able to come to your birthday party tomorrow.
The past of can is could. We use could especially with these verbs:
Let's see the following examples :
- When we went into the house, we could smell something burning.
- She spoke in a low voice but I could understand what she was saying.
- My grandfadher could speak five languages.
- When Tom was 16, he could run 100 metres in 11 second.
"Be Able To" To Express Capability of Doing Something in Particular SituationIf you mean that someone managed to do something in one particular situation, you have to use was/were able to
- The fire spread through the building very quickly but everyone was able (= managed ) to escape (not 'could escape ')
- They didn't want to come with us at first but in the end we were able (=managed)to persuade them. (not 'could persuade ')
- John was an excellent tennis player . He could beat anybody.(= He had the ability to beat anybody.)
- But once he had a difficult game against George. George played very well but in the end John was able to beat him (= He managed to beat him in this particular game.)
- My grand father couldn't swim.
- We tried hard but we couldn't persuade them to come with us.
2. I can 't understand martin. I've never been able to understand him .
3. I used to be able to stand on my head but I can't do it now.
4. Ask Ann about your problem. She should be able to help you.
5. I can speak five languages.
1. He had hurt his leg, so he couldn't walk very well.
2. She wasn't at home when I phoned but I was able to contact her at her office .
3. I looked very carefully and I could see a figure in the distance.
4. They didn't have any tomatoes in the first shop I went to, but I was able to get some in the next shop.
5. My grandmother loved music. She could play the piano very well.