1 knowledge, skill, strength etc: I can read Italian
We use can to say what people and things are able (or unable) to do because of their knowledge, skill, strength, nature, design etc.
I can read Italian, but I can’t speak it. These roses can grow anywhere. Dogs can’t climb trees. Can gases freeze? ?
Henry can lift 100 kilos. My car can do 180kph.
Be able to
(see be able) is used with similar meanings, especially when we are talking about people’s ability.
Henry is able to lift 100 kilos.
2 common or typical
We often use can to say what is common or typical.
Scotland can be very warm in September.
Ann can really get on your nerves sometimes.
3 possible in the situation: We can go to Paris
We also use can to say what we are able (or unable) to do because of the circumstances that we are in – what is possible in the situation.
We can go to Paris this weekend, because I don’t have to work.
I can’t come out this evening: I have to see my brother.
There are three possibilities: we can go to the police, we can talk to a lawyer, or we can forget all about it.
What shall we do?can and could : abilityWe can try asking Lucy for help.
Anybody who wants to can join the club.
4 past: She could read when she was four
We use could to talk about the past.
She could read when she was four.
My grandmother could sing like an angel.
My last car could do 200lcph.
In those days everybody could find a job.
It could be quite frightening if you were alone in our big old house.
Was able to
is also possible, especially to talk about people’s ability.
She was able to read when she was four.
5 past: could is not always possible
We use could for ‘general ability’ – for example to say that somebody could do something at any time, whenever he/she wanted.
When I was younger, I could run 10km in under 40 minutes.
We do not normally use could to say that somebody did something on one occasion. Instead, we use other expressions.
I managed to run 10km yesterday in under an hour, (not I could run 10km yesterday …)
How many eggs were you able to get? (not … could you get?)
After six hours’ climbing, we succeeded in getting to the top of the mountain.
(NOT … we could get to the top …)
I found a really nice dress in the sale, (not L-eeuld find …)
However, we use couldn’t to say that something did not happen on one occasion.
I managed to find the street, but I couldn’t find her house.
6 other uses of could
Could is not only past: we also use it as a ‘softer’, less definite form of can. What shall we do tomorrow?can and could : ability Well, we could go fishing.
When you’re in Spain, you could go and see Alex.
Could
can mean ‘would be able to’.
You could get a better job if you spoke a foreign language.
Could
is used in past indirect speech, when can was used in direct speech. Can you help me?can and could : abilityWhat did you say? can and could : abilityI asked if you could help me.
7 could have …
We use a special structure to talk about unrealised past ability or opportunities
– to say that somebody was able to do something, but did not try to do it; or that something was possible, but did not happen.
could have + past participle
I could have married anybody I wanted to.
I was so angiy I could have killed her!
Why did you jump out of the window? You could have hurt yourself.
I could have won the race if I hadn’t fallen.
This structure can be used to criticise people for not doing things.
You could have helped me – why did you just sit and watch?
Negative sentences suggest that somebody would not have been able to do something even if they had wanted or tried to.
I couldn’t have won, so I didn’t go in for the race.
I couldn’t have enjoyed myself more – it was a perfect day.
The structure is sometimes used to talk about past events which are not certain to have happened (like may I might have – see may and might 2: chances etc.7).
Who sent those flowers? can and could : ability I’m not sure. It could have been your mother.
8 chances: Will it happen? / Is it happening? Can not used
We do not use can to talk about the chances (probability) that something will actually happen, or is actually happening. Instead, we use may (see may and might 2: chances etc).
We may go camping this summer, (not We can-go …)
There may be a strike next week, (not There can be …)
Where’s Sarah?can and could : abilityShe may be with Joe. (not She can be …)
Some of these desserts may contain alcohol, (not … can contain …) However, could is possible in this sense.
It could rain later this evening, perhaps, (but not It can rain later …)
I could possibly have a new job soon, (but not I can possibly Imve-…)
For a comparison between can, could, may and might, see may and might 8: may/might and can/could.
For can’t used to express certainty (e.g. It can’t be true), see must 2: deduction concluding that something is certain.2.
For more information consult a good dictionary like Langman, Oxford, Merriam Webster, or Collins.