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

In the sentences "you could say", "you could use", "it could mean", does "could" here show possibility in the present? Which could means "may be able to"?

Hi Kirk,

Is the sentence "I am doing as much as I could" grammatical? I don't want to use "as I can" because it's a strong assertion, one that is a guaranteed activity. Rather, I want to project it as a suggestion of what I "can" do because I might not fulfill the promise of doing the activity at every possible opportunity even when I am able to.

Someone said I was wrong as the general rule is to use present tense throughout: "I am doing as much as I can." and "could" is only used for past or some other more obvious contexts.

Thanks

Thank you

Hello Grey101,

No, I'm afraid the sentence with 'could' is not correct. Although you're right that 'can' can imply more commitment than you want to express, it doesn't necessarily imply 100% commitment in the way you don't want it to. 'can' can imply that you are doing as much as circumstances (which can include your willingness to commit) allow.

Another option would be to change the phrasing. For example, you could say something like 'I'm doing what circumstances allow', though this is rather formal-sounding.

I hope this helps you.

All the best,
Kirk
The LearnEnglish Team

regarding the usage of "could have pp", it became somehow clear for me its usage in the past sentences but for future, is this sentence correct:
I have made my decision that up to two years later, I could(or should) have learned French language.
my problem root back to the way I was learned the modal verbs, I would always think should or would + have + pp only utilize when something should happen in past but for any reason, not happened or vise versa.
thanks a lot

Hello aria rousta,

Perfect modal verbs can have future meanings but they still need to have a retrospective sense. In other words, they are used with a sense of looking back. I think your example is rather ambiguous and would be clearer if you said 'within two years' or 'before two years pass' rather than 'up to two years later'.

This use of modals is sometimes called the future perfect. 'Will' is the modal verb most often used but other modals are possible, as you say. You can read more about the future perfect here and here.

 

Best wishes,

Peter

The LearnEnglish Team

Hi,

Pardon me if my following questions seem a bit superfluous, but I would appreciate it if you could confirm my understanding on the following: You mentioned under "Possibility", that could acts as the past tense of can. You then mention under "impossibility" and "ability" that could is used to talk about the past. By this, you simply mean that could serves as the past tense of can under "impossibility" and "ability"?

Also, my second question would be that under "possibility", you mentioned the use of could have to "show that something is/was possible now or at some time in the past". Quoting your example above, I suppose I could simply add a "not", as in "could not have arrived" to mean something is/was impossible, now or at some time in the past, and hence relegate this to be under the "impossibility" section?

Thanks!

Regards,
Tim

Hello Tim,

Each modal verb can represent multiple meanings. For example, 'could' can describe ability in the past:

When I was younger I could run 10km without any trouble.

It can also describe possibility in the present or the future:

The guests could be waiting for us already.

The guests could be here before 6.00.

You need to bear in mind that one modal has several uses/meanings and not try to fit all examples into one use.

This is why the modals section on the site is organised in the way it is, with sections showing different ways to express certain notions (possibility, obligation etc) and sections showing the different uses of certain modals (can, could etc).

 

The example you give of 'couldn't have' does represent impossibility from the point of view of the speaker. It is a form of deduction: the speaker does not know for sure but is convinced that it is not possible.

 

Best wishes,

Peter

The LearnEnglish Team

Hi Peter,

Thanks for the advice. Actually, I wanted to seek your clarification on the use of "could" to talk about the past, specifically under the sections of Possibility and Impossibility. Under Possibility, I note that Could may act as the past tense of Can. Under Impossibility, you mentioned couldn't/could not is used to "talk about the past" - does this mean that couldn't/could not is acting as the past tense of cannot/can't (e.g. He was obviously joking. He Could Not be serious)?

Thanks once again!

Regards,
Tim

Hi TIm,

Yes, that is correct. We phrase it quite cautiously on the page as we do not wish to suggest one-to-one correlations in this area when concepts such as possibility, deduced probability and so on overlap a lot and have very subtle distinctions between them.

 

Best wishes,

Peter

The LearnEnglish Team

could you please tell me the difference between two sentences which are :

_ i will wait for you in the airport
_ i will be waiting for you in the airport

thank you

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