词汇

grammar_british-grammar_could

释义

Could

Could: form

Affirmative (+) form

Could comes first in the verb phrase (after the subject and before another verb):

We could have lunch early.

Could cannot be used with another modal verb:

We could drive to France

Not: We could might drive to France. or We might could drive to France.

Negative (−) form

The negative form of could is couldn’t. We don’t use don’t/doesn’t/didn’t with could:

He couldn’t lift that. It’s too heavy.

Not: He didn’t could lift that …

We can use the full form could not in formal contexts or when we want to emphasise something:

Fabio was frightened. He could not move his arm. It was stuck.

Question (?) form

The subject and could change position to form questions. We don’t use do/does/did:

Could I pay by credit card?

Not: Do I could pay by credit card?

We use could and couldn’t in question tags:

I could come back tomorrow, couldn’t I?

Could: uses

Possibility

We often use could to express possibility in the present and the future.

Compare

It’s blue.

I am certain that it is blue. It’s a fact.

It could be blue. (present)

I’m not certain that it is blue.

The storm will get worse.

I’m certain that the storm will get worse.

The storm could get worse. (future)

I’m not certain that the storm will get worse.

See also:

Can: uses

Suggestions

We often use could to make suggestions:

A:
Will’s party is fancy-dress.

B:
It’s Halloween.

C:
Oh right. Icouldgo as Julius Caesar.

B:
Again? How many times have you done that?

A:
I’ve got to be in the meeting at 10 and the train doesn’t get in until 10.15.

B:
Couldyou get an earlier train?

Permission

We use could to ask for permission. Could is more formal and polite than can:

Could I ask you a personal question?

Warning:

We don’t use could to give or refuse permission. We use can:

A:
CouldI leave early today?

B:
Yes, you can./No, you can’t.

Not: Yes, you could./No, you couldn’t.

See also:

Can

Could: past

We don’t usually use could to talk about single events that happened in the past.

Past achievement

When actual past achievements are mentioned, we usually use was/were able to or managed to but not could in affirmative clauses. This is because they are facts, rather than possibilities:

I was able to/managed to buy a wonderful bag to match my shoes.

Not: I could buy a wonderful bag to match my shoes.

We hired a car and we were able to/managed to drive 1,000 miles in one week.

Not: We hired a car and we could drive 1,000 miles in one week.

Ability

We use could to talk about past ability:

When I was young, I could easily touch my toes.

Possibility

We use could have + -ed form to talk about possibility in the past:

I could have been a lawyer.

They could have taken a taxi home instead of walking and getting wet.

Janette couldn’t have done any better.

Guessing and predicting: couldn’t as the negative of must

When we want to guess or predict something, we use couldn’t as the negative form of must. We use couldn’t have + -ed form as the negative form of must have + -ed. Couldn’t and couldn’t have + -ed form express strong possibility:

She must have made a mistake. It couldn’t be true.

A firework couldn’t have done all that damage.

See also:

Can

Could + smell, taste, think, believe, etc.

We use could to refer to single events that happened in the past, with verbs of the senses (smell, taste, see, hear, touch, etc.) and mental processes (think, believe, remember, understand etc.):

The food was terrible. I could taste nothing but salt.

We knew they were in there. We could hear voices inside.

He came and spoke to me, but I couldn’t remember his name.

See also:

Be able to

Reporting can

We use could when reporting clauses with can as past events:

They told us we could wait in the hallway. (The original words were probably: ‘You can wait in the hallway.’)

She said we could book the tickets online. (The speaker remembers hearing ‘You can book the tickets online.’)

Criticism

We often use could have + -ed form to express disapproval or criticism:

You could have called to say you would be late. (You didn’t call – I think you should have called.)

You could have tidied your room.

Regret

We use could have + -ed form to talk about things that did not happen and sometimes to express regret:

He could have been a doctor.

I could have been famous.

We often use the expression how could you/she/he/they? to show disapproval (to show that we don’t like what someone has done):

Grandfather, how could you? How could you leave me?

How could you have gone without telling me?

A:
We had to give away our dog when we moved to England.

B:
Oh, how could you?

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