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

Hi all,
I have a question. Is it possible to use "could not be able to" in any context?

Thanks in advance.

Hello japezuela,

I think would not be able to... is far more likely in any context I can think of. Did you have a particular context in mind?

 

Peter

The LearnEnglish Team

Hi Peter,

Thanks for answering. I was thinking of, for example, in a situation in which it was too difficult for me, or out of the question, to be able to. Could I say, ' I could not be able to play a piano' referring to a past situation meaning " it was too hard for me playing the piano because I didn't have the necessary skills for doing so?

Thanks in advance.

Hi japazuela,

In that situation we would use either 'able to' or 'could', but not both together:

I could not play the piano.

I was not able to play the piano.

 

The only time we might use 'could' and 'able to' together is when we are using 'could' to talk about possibility rather than ability. In other words, 'could not be able to' might mean 'it is possible that [he/she] would not be able to...'

However, it is hard to think of a situation where we would use such a form, and I think other less ambiguous forms would be preferred in any case, such as 'could be unable to', 'might not be able to' or 'might lose the ability to'.

 

Peter

The LearnEnglish Team

Need your help in vetting the below statement for grammatical mistake

'Does AMS can lead to death? '

Pls.check & help me with corrections.

Hello gullu_summi

No, I'm afraid that's not correct. 'can' is a modal auxiliary verb and so 'do' is not used in a question. The correctly formed question would be 'Can AMS lead to death?'. I'd suggest you read our Question forms page for more on this grammar.

All the best

Kirk

The LearnEnglish Team

Hi could you please help me, what to write(can or could) in the following sentence.
'I am very hungry. I can/could eat a horse'. What's the correct answer?

Hello Garry301,

The correct form is 'could' because you are talking about a hypothetical situation (I could eat a horse if you gave me one) rather than a physical ability (I can eat a horse because I've got an enormous stomach).

 

Peter

The LearnEnglish Team

Hello, do these statements sound natural?
1. Yesterday I could have taken some rest, but I continued to work hard instead.
2. Though I was able to have some rest yesterday, I couldn't feel well enough to continue my work.
3. I could stop my work last year, but my parents talked me into proceeding it.
4. I could stay with you yesterday, but I had to go.
All the best,
Oleg

Hello Oleg,

The first sentence is fine.

The second sentence should say 'didn't feel' rather than 'couldn't feel'. This is because feeling well is not something we can do as we do not control it directly. We would use 'could' for something we are able to do.

The third and fourth sentences need to use 'could have' rather than 'could' as they describe unrealised past possibility.

 

Peter

The LearnEnglish Team

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