Page 132 - Practical English Usage 3ed - Michael Swan, Oxford

2
can and could (4): interpersonal uses (permission, requests etc) 124 One day people will be able to go to the moon on holiday.
(OR it will be possible to go ...) could in the past
Could is not normally used to say that somebody did something on one occasion in the past (see 122.5).
I managed to buy a really nice coat yesterday. (NOT : et)~1d b~y a really nice eoaf yesterddy.)
However, could can refer to one occasion with certain verbs: see, hear, taste, feel, smell, understand, remember and guess (see 125),
I could smell something burning. I could understand everything she said. And we can use could to talk about one occasion with words like hardly or only, that have a negative sense.
She could hardly believe her eyes. I could only get six eggs. Could can also sometimes refer to one occasion in subordinate clauses.
I'm so glad that you could come.
languages and instruments: She speaks Greek
We often leave out can when we are talking about the ability to speak languages or to play instruments.
She speaks Greek. / She can speak Greek. Do/Can you play the piano?
can/could a/ways
Can/could always can mean 'can/could ... if there is nothing better'.
I don't know what to get Mark for his birthday. "'" Well, you can always give
him a book token.
What are we going to eat?", We could always warm up that soup.
could have . .. for present situations
Could have + past participle can refer to present situations which were possible but have not been realised.
He could have been Prime Minister now ifhe hadn't decided to leave politics. We could have spent today at the seaside, but we thought it was going to
rain, so we decided not to.
3
4
S
124 can and could (4):
interpersonal uses (permission, requests etc)
1 asking for and giving permission: Can I ••• ?
We use can to ask for and give permission.
Can I ask you something?'" Yes, of course you can. You can go now ifyou want to.
Can't is used to refuse permission (often with other words to soften the refusal.)
Can I have some more cake?"'"No, I'm afraid you can't.
page 100