can and could: forms, ability

can and could: forms

1 Can is a 'modal auxiliary verb' .  There is no -s in the third person singular.

• She can swim very well (NOT She cans . . .)

Questions and negatives are made without do.

• Can you swim?(NOT Do you can swim?)
  


• I can't swim. (NOT / don't can swim.)

After can, we use the infinitive without to.

• I can speak a little English. (NOT / can to speak . . . )

2 Can has no infinitive or participles. When necessary, we use other words.

• I'd like to be able to stay here. (not . . . to can stay . . .)


• You'll be able to walk soon, (not You'll can ... .)


• I've always been able to play games well. (not I've always could . . .)


• I've always been allowed to do what I liked. (not I've always could . . .)

3 Could is the 'past tense' of can. But we use could to talk about the past, present or future.

• I could read when I was four.
  


• You could be right.


• Could I see you tomorrow evening?

Could also has a conditional use.

• I could marry him if I wanted to. ( = It would be possible for me to marry him . . .)

4 Contracted negative forms  are can't (/ka:nt/) and couldn't (/'kudnt/).
Cannot is written as one word.

5 Can and could are used in several ways. The main uses are:

• a   to talk about ability


• b   to talk about possibility


• c   to ask, give and talk about permission


• d   to make offers and requests, and to tell people what to do.

can and could: ability

1 Present

We use canto talk about present or 'general' ability.

• Look! I can do it! I can do it!
  


• I can read Italian, but I can't speak it.

2 Future

We use will be able to to talk about future ability.

• I'll be able to speak good English in a few months.
  


• One day people will be able to go to the moon on holiday.

We use can if we are deciding now about the future.

• I haven't got time today, but I can see you tomorrow.
  


• Can you come to a party on Saturday?

3 Past

We use could for 'general ability' — to say that we could do something at any time, whenever we wanted. (Was/were able to is also possible.)

• She could read when she was four. (OR She was able to ... )
  


• My father could speak ten languages.

We do not use could to say that we did something on one occasion. We use managed to, succeeded in . . . -ing, or was able to.

• How many eggs were you able to get? (NOT . . . could you get?)


• I managed to find a really nice dress in the sale yesterday. (NOT I could find . . .)


• After six hours' climbing we succeeded in getting to the top of the mountain. (NOT . . . we could get to the top . . .)

But we can use couldn't to say that we did not succeed in doing something on one occasion.

• I managed to find the street, but I couldn't find her house.

4 Conditional

We can use could to mean 'would be able to'.

• You could get a better job if you spoke a foreign language.

5 could have ...

We use a special structure to say that we had the ability to do something, but did not try to do it.

could have + past participle

• I could have married anybody I wanted to.


• I was so angry I could have killed her!


• You could have helped me — why didn't you ?