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'can' and 'could'

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




Hi AsahiYo20,

Can works fine in each sentence. However, the use is different in each example. The first sentence uses can to express possibility. The second uses can to express ability. This affects whether or not could can be used.


Even though if is not used, the first sentence is a form of conditional, expressing a condition and a dependent result. Could would make the sentences hypothetical and would require changes in the first clause:

A compromise would have to be reached between all the powerful vested interests before any restoration work in the city could take place.

[the speaker thinks the situation is unlikely]


In the second sentence, could would have a past meaning (past ability), and so the verb in the first clause would also need to be past:

I liaised with end-users, resellers and partners to see how we could improve our portfolio of products and services.



The LearnEnglish Team

Thanks for your detailed reply!

But am I correct to say that those two sentences refer to express future possibility and future ability respectively? If that is the case, I am confused about why "can" is used because I have the belief that "can" should not be used to talk about future possibility (expressed by could, may, might) or future ability (expressed by will be able to).

Hello again AsahiYo20,

The first sentence does not express future possibility but rather describes the present situation. It could be an answer to a question such as 'Why isn't the restoration work being done?', for example.


The second sentence is also not about the future. It describes a person's job in general terms, not a particular future event. It would be an answer to a question such as 'What does your job entail?' and not 'What are you doing next week?'



The LearnEnglish Team

Hi teachers,

1. Her colleagues could not fault her dedication to the job. --> Assuming that this sentence is not talking about the past, could I change "could not fault" to "cannot fault"?

2. The doctor examined her carefully but could find nothing wrong. --> could I delete "could" in this sentence? (i.e. ...but found nothing wrong.)

Thank you.

Hi patph0510,

1. 'Could' is referring to the past in this sentence. To say something is impossible in the present, we use 'can't' – but not 'couldn't' (see the first section above for some examples). So, your sentence with 'cannot fault' is the correct one for the present meaning.

2. Yes, you could. The meaning would be very similar, but with one difference: the version with 'could' includes the meaning of the doctor attempting or making effort to find the problem. The version without 'could' doesn't include that, and is focused on the end result (finding nothing wrong).

Best wishes,

The LearnEnglish Team

Hi teacher,

Thank you for your reply. As you said, and also according to a number of grammar books I have read, to say something is impossible in the present, we use 'can't'. But I sometimes see sentences using 'could (in a negative context)/could not' that seem to suggest impossibility in the present. Could you explain why 'could' is used in the following sentence?

"Nobody could take serious issue with his endorsement of the principle that police officers must be deterred from breaking the very laws they are empowered and entrusted to uphold"

Hi brian1010,

I can't be absolutely sure without knowing the full context of the sentence. But I think it's fine to use Nobody could ... to mean impossibility in the present because it uses could – not couldn't. If we make a version of the sentence using couldn't:

  • People couldn't take serious issue with ...

It isn't equivalent in meaning. It would be understood as referring to a past ability, not a present possibility. As you've seen above, could and couldn't have nuances in their meanings and aren't exact opposites, so could with a negative subject (e.g. Nobody could) isn't the same meaning as couldn't (for the meaning of possibility, at least).

For other meanings, could and couldn't may be more direct opposites. The sentences below about ability do have the same meaning.

  • Yesterday, nobody could answer the question.
  • Yesterday, people couldn't answer the question.

Does that make sense?

Best wishes,

The LearnEnglish Team

Hi teacher,

Are you referring to this section above: "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.)"

Does that mean we cannot use "could not" to convey a negative meaning in the sentences above because only "could", not "could not", can indicate a present possibility? Should we use "may not" instead if we want to convey a negative meaning?

Thank you.

Hi brian1010,

Yes, that's right. To say that those things are impossible for them to do, we can use can't or cannot, but not could not.

  • They can't come by car.
  • They can't be at home.

Using may not is possible, but the meaning is a bit different. May often indicates permission, so if we say They may not come by car, it means 'they cannot come by car because they don't have permission'. This usage of may not is also quite formal and emphatic.

Also, it might be confused with the 'not sure' meaning of may. They may not come by car (if there's no other context) would probably be understood as meaning 'I'm not sure whether they'll come by car or not', which is different from They can't come by car. So, I wouldn't recommend using may not for this meaning.

See this page for more explanation and examples about may

Best wishes,


The LearnEnglish Team

Thank you for your detailed reply. I would like to ask one more question as I just came across a sentence, which reads: "No one can say what might not happen if there were another earthquake."

I notice that the writer uses "can" rather than "could". Does that mean in the sentence I referred to earlier ("Nobody could take serious issue with his endorsement of the principle..."), "can" is also an acceptable alternative?