can or could

 

Possibility

We use the modal can to make general statements about what is possible:

It can be very cold in winter. (= It is sometimes very cold in winter)
You can easily lose your way in the dark. (= People often lose their way in the dark)

We use could as the past tense of can:

It could be very cold in winter. (=Sometimes it was very cold in winter.)
You could lose your way in the dark. (=People often lost their way in the dark)

We use could to show that something is possible in the future, but not certain:

If we don’t hurry we could be late. (=Perhaps/Maybe we will be late)

We use could have to show that something is/was possible now or at some time in the past:

It’s ten o’clock. They could have arrived now.
They could have arrived hours ago.

Impossibility:

We use the negative can’t or cannot to show that something is impossible:

That can’t be true.
You cannot be serious.

We use couldn’t/could not to talk about the past:

We knew it could not be true.
He was obviously joking. He could not be serious.

Ability:

We use can 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 to talk about the ability to do something at a given time in the present or future:

You can make a lot of money if you are lucky.
Help. I can’t breathe.
They can run but they can’t hide.

We use could to talk about past time:

She could speak several languages.
They couldn’t dance very well.

 

Permission:

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 if you like.
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 free.

Instructions and requests:

We use could you and 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 and invitations:

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 can give you a lift to the station.

 

Exercise

Comments

Hi Sir Peter and Sir Kirk,
how can i get command over the using of "can" and "could", still confusion exists regarding this, any advise plz share.

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

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

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