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 there,

Talking about "ability" what's the difference between "manage to" and "succeed in"? And how can they be compared to "can" or "be able to"?

Thanks in advance. You're the best, guys.

Hello Knightrider,

'Manage to' suggests that the activity was successful but difficult. 'Succeed in' suggests only that it was successful, but does not tell us if it was difficult or not.

'Can' is used for general ability, not specific achievements. 'Be able to' can be used for both general ability and specific achievements, but does not tell us if the task was easy or difficult.

I hope that clarifies it for you.

Best wishes,

 

Peter

The LearnEnglish Team

Everything's clear now, Peter. You've been most helpful. Thank you.

Regards.

Hello,

May I know whether the use of "could" in the following sentence is correct?

"Go and ask him whether he could differentiate the two."

If incorrect, could you please advise me the correct way to say it?

Thank you.

Hello Pocoyo,

That sentence is correct.  You could also use 'can' in the sentence, with a different meaning: 'could' implies a hypothetical situation in the sense that the person will not have to do it, and your question is purely speculative, while 'can' implies a real situation and that you want the person to try to differentiate between the two items for you.

Best wishes,

 

Peter

The LearnEnglish Team 

Hello Peter,

Thank you very much for your explanation! : )

there can be storm
there could be storm
the second one is used for uncertain situations.You said that can is used for possible situations..and the meaning of possible is "that may exist or happen, but that is not certain". So that means both can and could expresses possibility...So wats the difference between these two above sentences ???

Hello chatterjee,

The difference between "There can be storms" and "There could be a storm" is that the first sentence is talking in general about the climate in a place. For example, on Mt. Everest, there can be storms (at any time of the year). Here the sentence is about the climate there in general.

"There could be a storm" would be used to refer to a specific occasion. For example, if you're planning a trek to the Mt. Everest base camp and are thinking about what gear to take, you might want to take raingear as "there could be a storm" while you are on your trek. Here you're talking about a specific trek, not the climate in general.

As you can see, there is not really a difference in meaning here - it's more a question of use. I hope this helps you.

Best wishes,
Kirk
The LearnEnglish Team

sir as you said that can is used for general statements which are possible..Does this mean that "can" is used for showing 100 % surety..
For example - Using mobile phones while driving can be dangerous...Does this means that using mobile phones might be dangerous (more that 50% dangerous) or does that mean it is 100 % dangerous..??
As you said that can and could both are used to express possibility and could is used for uncertain...So does can expresses definite situations (100% possibility) or does it expresses a situation which is very likely to get happened (more possible than could but not 100% ) ???

i googled the meaning of possible and found that possible means "that may exist or happen, but that is not certain or probable." So possible in itself means uncertain..so why can is not used for uncertain situations...
Can i say that can expresses more possibility than could but not 100 % possibility.
For example -
1) There could be a storm later. (30-40 % possibility)
2) smoking can cause cancer. (70 % possibility but not 100 %)
Conclusion - can expresses more possibility compared to could but it does not expresses 100% possibility....Am i right ???

Pages