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

Section: 

Comments

Hello Lamastry,

I'm afraid that neither of these clauses are grammatical in standard English. Perhaps 'Let the whole word sing'?

Best wishes,
Kirk
The LearnEnglish Team

Hi Teachers, The LearnEnglish Team is very great and thank to you i daily keep improving my English.In order to these clauses above , i noticed some cases in which we can use " should" like in conditional clasues like these ones:1) should you pass by store, please get some bread 2) if you should pass by, say hello to him. another one (subjunctive) for istance: i suggested ironically that the audience should be given the earplugs. i wonder if there are any further cases we can use "should" like above.

i send you my regards.

Hello rosario70,

If you use 'should' in a first conditional sentence, it indicates that you think it's unlikely that the action will happen; in your first sentence, for example, it means you think it unlikely that the person will pass by a store. 'should' is also sometimes used after 'in case' to mean something like 'by chance'. For example, 'I'm going to make a note of our appointment in case I should forget it.'

Keep up the hard work – we're very glad to see you're making progress!

Best wishes,
Kirk
The LearnEnglish Team

Hello I heard someone saying this I'm her to confirm whether it is right or not In my opinion it is wrong "You have no marketing skills, you cant convince nobody" is it cant or can with nobody OR cant with anybody

Hello Lamastry,

You're right – the sentence you report is not standard English, though there are certainly a fair number of people, including native speakers, who say that. Here you should use 'anybody' instead of 'nobody'. See our indefinite pronouns page for more on this. And by the way, you could find this page yourself by searching for 'anybody' in our Search box.

Best wishes,
Kirk
The LearnEnglish Team

Thank you sir

what if I want to make a permission letter? Should I write on letter "dear sir, I would ask for your permission that I cannot attend your meeting today"? Or both of the modals are changed to would and could? Thank you

Dear Winson,

I expect you can find models of such letters by searching for them on the internet, and there are also some on these ESOLNexus and BBC pages. 'permission' is often followed by a to + infinitive, so I'd say something like '... your permission not to attend the meeting today', but check for examples on those pages for other ideas, too.

All the best,
Kirk
The LearnEnglish Team

What is the difference between could and may? I they both express the same thing, that is, could is used for hypothetical situation in the future.

John is coming to visit. He could stay with us.
John is coming to visit. He may stay with us.

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