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

Dear All friend
all friend can help me when we use can when we use could when we use be able to i'm from cambodai i hope all friend can help me!!!

Hello hsm hunsy!
 
Welcome to LearnEnglish! In answer to your question, there are two areas where we use be able to rather than can or could.
 
The first is to do with grammar. There is no v-ing, (xxxcanning swim is useful ), no infinitive (xxxI want to can swim), no future form (xxxI will can swim when I finish the lessons) or past participle (xxxI have can to swim since I was 7). In all these situations, we use be able to:

  • Being able to swim is useful.
  • I want to be able to swim.
  • I will be able to swim when I finish the lessons.
  • I have been able  to swim since I was 7.

We use could as the past of can, though: I could swim when I was 5.

The second time we use be able to is when we are talking about a single, special time, when we did something:
I lost my house keys. Luckily, I was able to climb in the window. (Not - I could climb through the window)

Hope that helps!
 
Jeremy Bee
The LearnEnglish Team

 

Hello There,
                     My question to you all is,can we use the modal  CAN and the adjective ABLE together in a sentence? Example: I can able to do five tasks at a time !

Hello Alchemist!
 
The short answer is - no, you can't! You don't put adjectives after can, and what do you think can able would mean, anyway?

If you use can/could to show possibility, then the following is OK:

I could be able to finish it by the end of the week if I work hard on it.

But you still need be!

Hope that helps,
 
Jeremy Bee
The LearnEnglish Team

hello  good day.
I have one question should i start from  tense or  general topic ?
for improving english.
thsnks in andvance
ajit

100%,i got.................

it's really helpful. i am learning a lot and hopefully it help me in future.

100% score...

Hi,
I just want to make sure if the question 5 of this exercise is grammatically correct?

Hello Fur4eng!
 
You're absolutely right - there was a mistake in the exercise. I have corrected it now; thanks for pointing it out! Let us know if you spot anything else, and enjoy the rest of the site.
 
Regards
 
JeremyBee
The LearnEnglish Team

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