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.


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]


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.


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?


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.


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 ...?
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


can and could: possibility 2


can and could: other uses 1


can and could: other uses 2




Hello Kirk.

I have a question, is it possible to use can with the verb know? Sometimes it sounds weird to me. For example in this sentences "consequently, humans can know everything about the world" isn´t it better to say human beings are able to know?


Hello yurico,

Both 'can' and 'be able to' are possible here. For example:

There are limits to what we can know about the far reaches of the universe.

There are limits to what we are able to know about the far reaches of the universe.

Both of these sentences refer to our ability.


Best wishes,


The LearnEnglish Team

Hello sir
Sir u can tell me about narration plz sir

Hello shah Muzamil,

Could you please be a bit more specific? For information on event recounts (which are a form of narrative) in an academic context, for example, our Writing for a purpose section has a few pages dedicated to this. If you're interested in the narrative tenses, please see our talking about the past and other pages in our English Grammar. Note there is a search box at the top of every page – press or click on the small magnifying glass.

All the best,
The LearnEnglish Team

Could someone advise me? Which one is correct : I don't know if I COULD come tomorrow / I don't know if I CAN come tomorrow.... Thanks in advance!

Hello Yura_Tea,

Both of these are commonly used and there is little difference between them. I would say that 'can' is more likely if the invitation has been made, while 'could' is more hypothetical, and is something we might say if we do not know whether or not we will be invited.

Best wishes,


The LearnEnglish Team

Hello sir, is this a correct sentence?
I called you by the reference of _(name of person)
will you tell me when can I come?

Hello Bharti,

No, that's not idiomatic – I'd suggest 'on the advice of someone'. The word order in the reported question is not correct: 'Will you tell me when I can come?'.

Best wishes,
The LearnEnglish Team

Hello sir, where we use 'can 'or can be?

Hello B H A R T I,

'be' is a bare infinitive, which is the form used after 'can' and other modal verbs. 

All the best,
The LearnEnglish Team