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 ?
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