Page 130 - Practical English Usage 3ed - Michael Swan, Oxford

Henry can lift 100 kilos. My car can do 180kph.
Be able to (see 3) 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? '" We 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 200kph.
In those days everybody could find a job.
It could be quite frightening ifyou 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.
S 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 lOkm 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 : etJltlt:l run IfJknt yesterday .. .)
How many eggs were you able to get? (NOT ••• OOfllt:l ytlfl get?)
After six hours' climbing, we succeeded in getting to the top ofthe mountain.
(NOT ••• we etJfllti get to the top ...)
I found a really nice dress in the sale. (NOT .. etJltlt:lflnd •..)
However, we use couldn't to say that something did not happen on one occasion.
1managed 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? '" Well, we could go fishing.
When you're in Spain, you could go and see A~.
Could can mean 'would be able to'.
can and could (2): ability 122
page 98