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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 sir
1. John could be the one who stole the money.
2. John could have been the one who stole the money.

3. John could go to jail for stealing the money.

All these sentences denoting possibility....first sentence denote present possibility 2nd past and 3rd future.........In first sentence there is past form of verb(stole) instead of base form.....Why?Though the sentence is denoting present state and we r giving an opinion.........
Q=1. If I had more time, I could travel around the world.
2. If I had had more time, I could have traveled around the world.

3. If I had more time this winter, I could travel around the world.

All these sentences also denoting possibilities...........i couldn't make any difference between them.............

Hello Learner S,

The verb 'stole' is a past form because it describes past time - the stealing took place in the past.  We have an opinion now ('could be') about someone who did something in the past.

In your second set of sentences you have different time references:

1 - hypothetical present

2 - hypothetical past

3 - hypothetical future

I hope that helps to clarify it for you.

Best wishes,

 

Peter

The LearnEnglish Team

Thanks sir this elaboration really helped me a lot.........

Hi, for future possibility, we should say "This could be you." to indicate an aspiration especially when it's referred to a specific picture or person description. But if we say "This can be you.", will it increase the possibility, ie, it's no longer a future possibility and it's very likely, it's real?

Would love to hear your comments. Thanks.

Hi er555,

I'm not sure I'd say could indicates an aspiration here - it's more that the possibility exists, and there is a sense that it depends on some unnamed conditions (e.g. "if you exercised every day").

Changing could to can would indeed indicate that the possibility is greater - perhaps the condition would be "if you exercise more". This is not a reality, but by using the present simple (you exercise), the condition is regarded as being more likely.

Best wishes,

Kirk
The LearnEnglish Team

hi sir,
i want to know difference between both following statements,
(1) If we don’t hurry we could be late.
(2) If we don’t hurry we can be late.

Hi Baloch Faisal,

We would rarely if ever use the second sentence in English.  This is because the sentence is referring to something in the future which is possible but not certain and for this meaning we use the modal verbs could, may or might.  You can learn more about this here.  Can is used to talk about in more general terms about what is possible, as you can see from the explanation at the top of this page.

I hope that helps to clarify it for you.

Best wishes,

 

Peter

The LearnEnglish Team

Sir Peter,
so what will i think that is second sentence wrong ?

Hi Baloch Faisal,

Yes, I would say that it is incorrect. Perhaps there is some unusual situation in which it might work, but I can't think of one. As Peter says, it would be far more normal to use might, may or could instead of can here.

Best wishes,

Kirk
The LearnEnglish Team

Hi! I'd like to ask if "I can imagine how varieties of sarcasms WOULD be preponderant on existing social networking sites in replacement of vulgar remarks and nasty comments." is correct. I have doubts though. Thank you.

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