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.





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."?

Hello binhle410,

We say 'could have been' when something was possible but did not happen. For example, if I say I could have taken the train then it means that taking the train was possible, but I did not do it.

Your second sentence means that your teacher had the choice of being very strict, but chose differently.


Best wishes,


The LearnEnglish Team

sir plz. tell me this
I --------- ride a bike, but I not swim when I ---------- was seven year old.

a can
b could
c both a and b

Hello umer,

I'm afraid that the sentence after 'but' doesn't make sense to me, so I can't really help you with that part - I think there must be an error in it. And the first answer depends on the second part of the sentence. In any case, if this is homework, you should really ask your teacher for help or at least explain what you think the answer is and why. That way you can learn much more.

All the best,
The LearnEnglish Team

hello sir
my teachers say that the answer is b (could)
but some says c (both a and b) sir tell me the answer plz I am very confused

your regards

Hello again umer,

'could' certainly makes sense for the first gap, but, as I said in my previous comment, the rest of the sentence is not grammatical, so I'm afraid there is no answer for the second gap that would make the sentence correct; certainly neither 'could' nor 'can' makes sense to me there.


In any case, since the sentence refers to a past time (when the subject was seven years old), 'could' is more correct than 'can' in general. Then the sentence could be 'I could ride a bike, but not swim when I was seven years old'.

All the best,
The LearnEnglish Team

Hello, Sir in the section that is talking about making a polite offer and the examples are
'Could I give you a lift?'
'I could carry that for you'.
I have read If we use 'could' we sound less certain that the offer will be accepted and 'could' is used when we want the offer to sound more tentative.
So I really get confused to use 'could' instead of 'Can' To make a polite offer
So, could you please help me to know the difference?
and the examples:
'How can I hep you?
'Can I help you?'
'Can I help you in any way?'
are the same if we say:
'How could I help you?'
'Could I help you?'
'Could I help you in any way?'
Thank you, Sir

Are there any other way to use could in present other than could be and could have?

For using could in present could be is used.for using could in past it can be used as past ability as well as could have in conditionals.for using could in future could is used for possibilty not for ability am I right

hello sir,i have gone through the explanation this section provides but i still have some doubts.1)If i say these things could kill you,does it mean that there is a possibility of these things killing me or certainty of getting killed?what would happen if we replace could with can in this statement?
2)in a question,what difference will it make if we replace could with can or visa versa?