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

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 ???

Hello chatterjee,

When can is used to make a general statement like this, the focus is on what is possible, not how probable it is. To talk about probability or possibility in a more specific context, could, may or might are generally used.

I'd recommend that you pay attention to how can and could are used in context, i.e. in written texts and in conversations (see our Magazine for lots of articles), because you can get a much better sense of their meaning when there is some kind of meaningful context. These grammar exercises are meant to give you a start and to help you understand some of the finer points but the real test is to understand them in use in oral or written texts. Both can and could are used extensively, so almost anything you read will have examples of them.

Best wishes,
Kirk
The LearnEnglish Team

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

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