could S1 W1 /kəd; strong kʊd/ modal verb (negative short form couldn’t)
[Language: Old English; Origin: cuthe, past tense of cunnan ( ⇒ can¹); influenced by should and would]

1. PAST ABILITY used as the past tense of ‘can’ to say what someone was able to do or was allowed to do in the past:
By the time she was eight, she could read Greek and Latin.
In those days you could buy a box of cigars for a dollar.
Could you hear what I was saying?
I couldn’t get tickets after all, they were sold out.
I knew I couldn’t afford the rent.
The teacher said we could all go home.

2. POSSIBILITY
a) used to say that something is possible or might happen:
Most accidents in the home could be prevented.
It could be weeks before we get a reply.
If you’re not careful, you could get into even worse trouble.
A faulty connection could easily (=would be likely to) cause a fire.
b) used to say that something was a possibility in the past, but did not actually happen:
Somebody could have been killed.
I could have warned you if I had known where you were.
He could have escaped, but he chose to stand and fight.

3. EMPHASIZING YOUR FEELINGS spoken used to emphasize how happy, angry etc you are by saying how you want to express your feelings:
He irritates me so much I could scream.
I was so angry I could have killed her.
I was so relieved I could have kissed them all.

4. REQUESTING spoken used to make a polite request:
Could you help me with these boxes?
Could I have a drink of water, please?
How about Sam? Could he come along too?
I wonder if I could just ask you to sign this.

5. SUGGESTING used to suggest doing something:
You could ask your doctor for a check-up.
You could always try phoning her at the office.
Maybe we could get together sometime next week?
Couldn’t you get one of your friends to help you?

6. ANNOYANCE spoken used to show that you are annoyed about someone’s behaviour:
You could have told me you were going to be late (=you should have told me but you did not)!
You could at least say that you’re sorry.
How could you be so stupid!

7. couldn’t be better/worse/more pleased etc used to emphasize how good, bad etc something is:
Their lifestyles couldn’t be more different.
‘How are things?’ ‘Fine! Couldn’t be better.’
Ordering online couldn’t be simpler.

8. I couldn’t British English spoken used to politely say that you do not want any more food or drink:
‘Would you like another piece of pie?’ ‘Oh, no thanks, I couldn’t.’

9. could do with something spoken to need or want something:
I could do with a hot drink.
⇒ could do worse (than) at worse¹(5), ⇒ couldn’t care less at care²(5), ⇒ couldn’t agree more at agree(1)

[TahlilGaran] Dictionary of Contemporary English ▲

could
modal verb
1.
BAD: As I've already mentioned, I could learn a great deal during the two years I spent in England.
GOOD: As I've already mentioned, I was able to learn a great deal during the two years I spent in England.
BAD: By reading quickly, I could finish the book before the library closed.
GOOD: By reading quickly, I managed to finish the book before the library closed.

Usage Note:
When talking about a skill or general ability in the past, use could or be able to : 'By the time she was four, she could/was able to swim the whole length of the pool.'
When talking about a single event in the past, we usually use be able to or manage (NOT could ): 'Luckily, we managed to get there before the shops closed.' 'Were you able to start the car?'
See also ABLE 2 (able)

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2.
SEE POSSIBLE 2

[TahlilGaran] Dictionary of Common Errors ▲