Possibility

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

It can be very cold in winter. (= It is sometimes very cold in winter)
You can easily lose your way in the dark. (= People often lose their way in the dark)

We use could as the past tense of can:

It could be very cold in winter. (=Sometimes it was very cold in winter.)
You could lose your way in the dark. (=People often lost their way in the dark)

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

If we don’t hurry we could be late. (=Perhaps/Maybe we will be late)

We use could have to show that something is/was possible now or at some time in the past:

It’s ten o’clock. They could have arrived now.
They could have arrived hours ago.

Impossibility:

We use the negative can’t or cannot to show that something is impossible:

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

We use couldn’t/could not to talk about the past:

We knew it could not be true.
He was obviously joking. He could not be serious.

Ability:

We use can 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 to talk about the ability to do something at a given time in the present or future:

You can make a lot of money if you are lucky.
Help. I can’t breathe.
They can run but they can’t hide.

We use could to talk about past time:

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

 

Permission:

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 if you like.
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 free.

Instructions and requests:

We use could you and 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 and invitations:

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 can give you a lift to the station.

 

Exercise

Section: 

Comments

Hey :) 2 questions please
1-Is this grammatically correct? 2- is it better to use could or can ?

"That story is the one that keeps me going whenever I hit my point or think that I ( couldn't ) do it anymore."

Hello Ahmedkhairy,

I'm not sure we'd say 'hit my point' in this way. I think 'I've had enough' would be better. The sentence would be:

That story is the one that keeps me going whenever I've had enough or think that I can't do it anymore.

I would say that can't is required here rather than couldn't as the whole sentence refers to general (present) time, not past time. We can use could with present meaning when talking about possibility, but here the meaning is ability, and when talking about ability could is used only with a past meaning.

 

Best wishes,

Peter

The LearnEnglish Team

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?

Thanks.

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,

Peter

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,
Kirk
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,

Peter

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,
Kirk
The LearnEnglish Team

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