Page 131 - Practical English Usage 3ed - Michael Swan, Oxford

can and could (3): ability (advanced points) 123
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Could is used in past indirect speech, when can was used in direct speech.
Can you help me?- What did you say?- I asked ifyou 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 angry 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/might have - see 339.7).
Who sent those /lowers? '"" I'm not sure. It could have been your mother. S chances: Will it happen? lis 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 339).
We may go camping this summer. (NOT We ean ge ...)
There may be a strike next week. (NOT There can be ...)
Where's Sarah?-She may be with Joe. (NOT She can be ...)
Some of these desserts may contain alcohol. (NOT ••• can oontain ...)
However, could is possible in this sense.
It could rain later this evening, perhaps. (BUT NOT it can railt iatet' ...) I could possibly have a new job soon. (BUT NOT I eat'/; ""ssibly Mlle . ..)
For a comparison between can, could, may and might, see 345. For can't used to express certainty (e.g. It can't be true), see 359.2.
123 can and could (3): ability (advanced points)
1 future: can or will be able
We use can to talk about future actions which we will be able to do because of present ability, present circumstances, present decisions etc.
She can win the race tomorrow ifshe really tries.
I've bought the tent, so we can go camping next weekend if we want to. I haven't got time today, but I can see you tomorrow.
Can you come to a party on Saturday?
In other cases we prefer other structures, for example will be able to. I'll be able to speak French at the end ofthis course.
(NOT {can speak French ...)
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