Level: beginner

Possibility and impossibility

We use could to show that something is possible, but not certain:

They could come by car. (= Maybe they will come by car.)
They could be at home. (= Maybe they are at home.)

We use can to make general statements about what is possible:

It can be very cold here in winter. (= It is sometimes very cold here in winter.)
You can easily get lost in this town. (= People often get lost in this town.)

We use can't or cannot to say that something is impossible:

That can't be true.
You cannot be serious.

Level: intermediate

We use could have to make guesses about the past:

It's ten o'clock. They could have arrived by now.
Where are they? They could have got lost.

We use could to make general statements about the past:

It could be very cold there in winter. (= It was sometimes very cold there in winter.)
You could easily get lost in that town. (= People often got lost in that town.)

We use can't have or couldn't have to say that a past event was impossible:

They know the way here. They can't have got lost!
If Jones was at work until six, he couldn't have done the murder.

Ability

Level: beginner

We use can and can't to talk about someone's skill or general abilities:

She can speak several languages.
He can swim like a fish.
They can't dance very well.

We use can and can't to talk about the ability to do something at a specific time in the present or future:

I can see you.
Help! I can't breathe.

We use could and couldn't to talk about the past:

She could speak several languages.
They couldn't dance very well.

Level: intermediate

We use could have to say that someone had the ability or opportunity to do something, but did not do it:

She could have learned Swahili, but she didn't want to.
I could have danced all night. [but I didn't]

Permission

Level: beginner

We use can to ask for permission to do something:

Can I ask a question, please?
Can we go home now?

could is more formal and polite than can:

Could I ask a question please?
Could we go home now?

We use can to give permission:

You can go home now.
You can borrow my pen if you like.

We use can to say that someone has permission to do something:

We can go out whenever we want.
Students can travel for free.

We use can't to refuse permission or say that someone does not have permission:

You can't go home yet.
Students can't travel for free.

Requests

We use could you … as a polite way of telling or asking someone to do something:

Could you take a message, please?
Could I have my bill, please?

can is less polite:

Can you take a message, please?

Offers

We use can I … to make offers:

Can I help you?
Can I do that for you?

We sometimes say I can ... or I could ... to make an offer:

I can do that for you if you like.
I could give you a lift to the station.

Suggestions

We use could to make suggestions:

We could meet at the weekend.
You could eat out tonight.

Questions and negatives

We make questions by putting the subject after can/could:

Can I ...?
Could I ...?
etc.
Can you ...?
Could you ...?

 

The negative form is can't in spoken English and cannot in written English.

We sometimes say cannot, but it is very emphatic.

The negative form of could is couldn't in spoken English and could not in written English.

can and could: possibility 1

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can and could: possibility 2

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can and could: other uses 1

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can and could: other uses 2

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Comments

Hello Oleg,

That sentence is not correct and I'm not sure what you want to say in the second half, to be honest. It looks like you've translated something from your own language word for word, but it doesn't produce clear English.

Generally, we don't provide a checking or correction service on LearnEnglish. We are a small team and there is a very large number of users on the site, so it's simply not possible for us to do this for everyone.

 

Peter

The LearnEnglish Team

Hello,

Please, explain me what is the use of could here: 'After the accident a number of other people gathered round the car, but there was not a great deal we could do.' I would reckon that is just past from can (general ability), denoting 'were able to do'?
All the best,
Oleg

Hello Oleg

Yes, that's correct -- good work!

All the best

Kirk

The LearnEnglish Team

Hello,

Could you please view upon this. Would 'the burglar could get in through the window' followed by 'but later he changed his qualification for pickpocket' be correct? )
All the best,
Oleg

Hello,

If I was asked ' where is the boss?' and wanted to make fun of him, would it be correct to say:
Oh! He can be in his office (as a fact, implying that he can't care less about his being or not being in the office)?
All the best,
Oleg

Hello Oleg

It sounds to me as if you're talking about a possibility that you're not certain of; in this kind of situation, 'can' is not correct -- I would suggest 'could' instead. 

All the best

Kirk

The LearnEnglish Team

Thank you, Kirk.
All the best, Oleg

if she is single today, i could have married her.
Am i correct?
means - the ga
if this gal is unmarried , i can mry

Hello Ali. Chy

No, I'm afraid that's not correct. I'm not completely sure what you want to say, but 'If she is single, I could marry her' is grammatically correct and logical.

All the best

Kirk

The LearnEnglish Team

What would be the correct way of asking a teacher to meet me the next day?

1. May I meet you tomorrow, please?

2. Could we meet tomorrow, please?

3. May we meet tomorrow, please?

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