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 mmoaazhameed,

When the explanation above says 'offers and invitations', 'invitation' means essentially the same thing as 'offer'. So, for example, you could say to a person who looks lost on the street: 'Can I help you?' or 'Could I help you?' – these are offers or invitations to help.

Our sister site LearnEnglish Teens has a video that explains this grammar as well as a few additional practice exercises if you'd like to work on this more.

All the best,
The LearnEnglish Team

i have an other question. are both formations correct?

"the best you could say" vs "the best you can say"?
( you could say to a person who looks lost on the street or you can say........?)

Hello mmoaazhameed,

I'm not clear on the context of the sentence. Is this part of a dialogue? Has the person on the street asked you something? Before we can answer we need to know the context, as this is crucial in determining whether 'can', 'could' or both are correct.


Best wishes,


The LearnEnglish Team

thank alot kirk! :)

I have a question about this sentence "what we would do if the world was different" could it be possible if i replace the modal "would" in the example sentence with "could". What we could do if the world was different? How the could sentence differs from the former? Im really confused with can and will although there are some particular use of these modals but sometimes they are used in a sentence in which they can mean the same. how will i know if im going to use can and will. thank you very much

Thanks for the reply. Im still a bit confusedwhat if I used would and could like this "If we dont hurry we could be late" and "if we hurry we would not be late". Is it also possible that I use would in your example "if we dont hurry we would be late"? Is this mean that if I use could this means it is proble there is chance wherein if I use would you are going to be late and sure about it? Thank you

Hello RTris,

'Could' in these examples describes possibility while 'would' describes a sure result, provided the condition is fulfilled. However, your examples are conditional forms and the forms in the second clause must agree with the verb form in the first clause:

If we dont hurry we could be late - this describes a possibility; it is possible that we will be late

"If we hurry we would not be late - this sentence is not consistent. You can say 'If we hurry we will not be late' (describing the result of a possible or likely condition) or you can change the first clause and say 'If we hurried we would not be late' (describing the result of a hypothetical or unlikely condition).


Best wishes,


The LearnEnglish Team

Hello RTris,

Both 'would' and 'could' are possible. If we use 'would' then we are talking about our choices or decisions in a particular situation (a different world). If we use 'could' then we are talking about what is possible in that situation.

You can think of it like this: what we could do is everything that is possible; what we would do is which of those possible things we choose. For example:

If it rained I could stay at home or go out. I like walking in the rain, so I think I would go out.


Best wishes,


The LearnEnglish Team

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,


The LearnEnglish Team