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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.

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, I want to know why 3rd form of find is used in below sentence. I mean which grammar is that.

The typhoid bacteria can be found in contaminated food or water.

tnx

Hello AK47,

'can be found' is a passive construction consisting of the modal verb 'can' and the bare infinitive of the verb 'find' in the passive voice. On the pages that I've linked to, please note that 'found' is called a past participle - this is just another name for 'third form'.

Best wishes,
Kirk
The LearnEnglish Team

Can I show my writing sample to illustrate which is my question?

Hello ricrodri,

As is explained in more detail on our Help page, you're welcome to ask us a specific question about something you've written, but we don't have the time to give feedback on whole pieces of writing.

Best wishes,
Kirk
The LearnEnglish Team

hi teacher now i studying the different between can, could, be able to or was able to ...could teacher explain to me when we used modal these? i make confusion because be able to is similar the modal...what are the tips for not mistake in sentence ?
thanks teacher .

Hello davide32,

You can find information on modal verbs on our grammar pages. Click here to go to our modal verbs page, where you'll find links to pages focusing on particular modals.

Best wishes,

 

Peter

The LearnEnglish Team

Adding to my previous question, I'm not sure about this one eithe "you better don't be slow, or your dreams could/ can pass you by" Which one would be more appropiate? And/or what would be the difference between them?. Thanks in advance to all the team and keep up the good job :)

Hello,

Both of them are possible, but 'could' suggests more of an imaginary situation and 'can' more of a real situation.

Best wishes,

Adam
The LearnEnglish Team

Hi there! I'm doubtful about this sentence: "why should I feel fear? Fear could later become regret" using can instead would be more appropiate? Or what would be the difference?

Hi,

The meaning in that sentence is covered under 'possibility' above. So 'could' sounds better in this sentence, as it's talking about something that's possible in the future, but not certain.

Best wishes,

Adam
The LearnEnglish Team

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