can, could and could have


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.




can i use could with negative in questioning for present situations.

for example:
i couldn't buy the book to learn english.
because when i can use,''i couldn't be there" for possibility in present,why cannot i use bare verb in present for possibility?
if i can use this for present to show possibility,what changes i have to make to show ability in past?
Nandish BC.

Hello Nandish BC,

The sentence would probably be 'I couldn't buy the book for learning English' and it describes a past possibility (or lack of possibility), not a present one: 'I couldn't buy the book [this morning]'.

Best wishes,


The LearnEnglish Team

can we use "could" for expressing something that could possible in near future.

Example :
1) i could fall in the trek.
2) i could fall while trekking.

could you help me in understanding "could" usage.

Hello bharathkumarreddy,

Yes, we can use 'could' that way, and those sentences are fine.

Best wishes,



The LearnEnglish Team

Team British Council,

I just found that using "CAN'T HAVE" instead of "COULD HAVE" and have read in some grammar books.I am confused on this right now.Find below written sentences and is it gramatically correct? or What is the meaning of it if we use it?
They can't have started function.
She can't have done it.

Manu K Joy

Hello manumkj,

'Can't have' is an example of a perfect modal verb and is used when we are speculating or making logical deductions about the past on the basis of some evidence or expectation.

There are five modal verbs typically used in this way:

He must have lived in Paris. (I'm sure this was true)

He could/might/may have lived in Paris. (It's possible this was true)

He can't have lived in Paris. (I'm sure this was not true)

The modal verbs in your sentences are correct; however, we would say 'the function' rather than just 'function'.

I hope that helps to clarify it for you.

Best wishes,



The LearnEnglish Team

sir can we substitute could or might for would in conditional....please let me know,,,

Hello maxamun,

Your question is too general. We use 'would' in many different ways in conditionals and some uses can be replaced by other modal verbs while others cannot. If you provide a specific example then we'll be happy to tell you if 'might' can be used or not.

Best wishes,



The LearnEnglish Team

hello sir, i have a huge confusion...such as..i could do it( as past possibility not ability) it possible to say that i could do that(but i didnt) like i could have done that.......another is....i could have done that(but i didnt) but i couldnt have done that(is that mean i did or what) an example..i couldnt have called you if i hadnt bought a mobile...(is that mean i made a call)....please please please sir hepl me out.....

Hello maxmamun,

I'm afraid it's very hard to understand your question, and we can't answer a question which we do not understand! To help us, please ask about one thing rather than several at once and please start with a concrete example, then ask about that example rather than starting with a very general question and adding a sentence at the end.

Best wishes,



The LearnEnglish Team