Questions and negatives:

We make questions by putting the subject after can/could:

Can I …? Can you …? Could I … Could you …? and so on.

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.
We sometimes say could not.

We use can and can’t :

  • To talk about ability:

Maria can speak four languages.
I can’t swim, but my sister can.

  • To say that something is possible or impossible:

Learning English can be difficult [= Learning English is sometimes difficult.]
Children can be very naughty [= Children are sometimes very naughty.]
It’s still light. It can’t be bedtime.

  • For requests and refusals of requests

Can I go home now?
You can go whenever you like.
You can borrow the car today, but you can’t have it tomorrow.

  • To offer to help someone:

Can I help you?
Can I carry that bag for you?

We use could and couldn’t as the past tense of can/can’t:

  • To talk about ability:

I could run very fast when I was younger.
She couldn’t get a job anywhere.

  • To say that something was possible or impossible:

Our teacher could be very strict when we were at school. [= Some teachers were very strict.]
People could starve in those days. [= People sometimes starved.]
You couldn’t use computers in the nineteenth century.

  • To make a polite request:

Could I go now please?
Could you lend me a dictionary please?

  • To make a polite offer:

Could I give you a lift?
I could carry that for you.

We use could have:

  • to show that something is possible now or was possible at some time in the past:

It’s ten o’clock. They could have arrived now.
They could have arrived hours ago.





Could you, please, explain this: They can't have left us without saying goodbye. Is this correct to use such a structure 'can't have left'?

Hello vvst78,

Yes, 'can't' + verb is commonly used to say we believe that something is not possible (e.g. 'You can't be tired - you've just woken up!') and 'can't have' + past participle is used in the same way to talk about something in the past. Take a look at the 'must as deduction' section of this BBC page for more on this.

All the best,
The LearnEnglish Team


Thank you very much!

My question is , regarding the usage of could in showing past ability of something :
A) Telegrams "could be" sent through post offices in 1879.
B) Telegrams "could have been " sent through post offices in 1879.
Which one is correct ? What is the difference ?
Thank you

nice Qus.

Hello viknikwins,

A is making a general statement that it was possible at that time. B is a bit unusual out of context (though correct) – it suggests that it was possible but not done. 'could have' is often used to express that it was possible to do something, but that it was not done, e.g. 'I could have studied in London' (but studied in Manchester instead).

All the best,
The LearnEnglish Team

Kirk i read somewhere :
"What better gift could it have been . "

And what i think after reading your answer it should have been "what better gift could it be than this. " Usage of could in past. Am i right?

Hello viknikwins,

There is a time difference here and it relates to whether or not the present has been given.

If you use 'could it have been' then the giving is completed and any change to the gift is impossible; the sentence describes a hypothetical past. For example, you might be reflecting on a gift which was given to a friend yesterday.

If, on the other hand, you use 'could it be' then you are talking about a gift which has not been given and so might still be changed. For example, you might say this when you are standing in a shop considering whether or not to buy something as a gift for someone.

Remember that modal verbs have many meanings and the form depends upon the meaning. For example, 'could' can describe ability in the past, present possibility, deduced probability and more, as you can see in the information on this page.

I hope that helps to clarify it for you.


Best wishes,


The LearnEnglish Team

Thank you kirk. Somebody told me that you can not use "could be " for past ,that is where confusion came from . Now it is clear .

To say that something was possible or impossible:
Our teacher could be very strict when we were at school. [= Some teachers were very strict.]
===> Please tell me what difference it would make if we say
"Our teacher could have been very strict when we were at school."?