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

Hi !
I have to use in this sentence a modal verb "it's not possible that he heard about it on the radio. He never listen to the news.".
I wrote " he couldn't have heard about it......." But apparently it's wrong. Could someone explain me why, please?

Hi Gager,

As far as I can see 'could have' would be fine as a way of expressing that meaning. If you want to know why it was not accepted then you will need to speak to the person who made that decision.

 

Best wishes,

Peter

The LearnEnglish Team

But you couldn't made me laugh.
Is the sentence correct?

Hello Pratiksha Chauhan,

No, it is not. Modal verbs such  as 'could' (including the negative form 'couldn't') are not followed by past simple forms like 'made'. In this case, 'make' is probably your best option, though 'have made' is also possible.

All the best,
Kirk
The LearnEnglish Team

Thank you Sir.

What's the mistake in it?
He had travelled so much that he could assess the relation between the state and the society at one's airport.

Hello Asgharkhan8,

'the' is probably not needed before 'society' (whether or not it should be used depends on what the sentence means precisely) and 'one's' is also a bit unclear out of context.

All the best,
Kirk
The LearnEnglish Team

Plz read it and tell me my mistakes

My friend asked me to elaborate some topics related to his course. When he asked I had exams on very next day, that’s why we have shortage of time and it was difficult for me to manage this. The topic was little tough to explain in short time period. At last I managed and put all my efforts to explain that topic but it was all in vain. Because he had fear of exam, and he messed all the topics, and got confused, he could not focused on it. I gave my level best but it did not work at eleventh hour. I control my aggression and treat him very politely till end then I realised all my attempts didn’t achieve the desired outcomes. I decided not to bother and left him.

Hello mehdiraza,

Thank you for your comment. I'm afraid we don't offer a correct service for our users, however. We are a small team here and the site has many thousands of users, so it is just not possible for us to do this - and, of course, we would simply end up checking users' schoolwork for them! We do, however, read every comment which is made on the site and we are happy to help where we can with particular aspects of the language.

 

Best wishes,

Peter

The LearnEnglish Team

Which is correct?

-I'm not sure if I can bring....
-I'm not sure if I could bring....

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