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.

 

Exercise

Section: 

Comments

Hi

While I understand the use of "could have", would there be such a thing as "can have"?

Regards,
Tim

Hello Tim,

We do not use 'can have' as a perfect modal. We do use 'can't have', however, in order to express a logical deduction of a past event:

He can't have left the building because we would have seen him.

 

Best wishes,

Peter

The LearnEnglish Team

Hello ,Sir. I hope you are doing well. My question is that you have used the usage of can (Requests or Refuse Requests) , moreover the sentence that has made me strained is , "Can I go home now?" I want to know whether this sentence shows "request" or "permission". Thanks a million in advance.

Hello nadarali1996,

Giving or asking for permission is a specific kind of request -- you are requesting someone for permission. Does that make sense?

All the best,
Kirk
The LearnEnglish Team

Also, please in the following sentence, do we use 'could come' or 'would come'?
- He can't come tomorrow, I wish he ............

Hello ExistentialAwareness,

With can't in the first clause you have already established that not coming is not his choice but something which is imposssible for him. It would, therefore, not be logical to use would in the second clause as this refers to choice or preference. Could is the only logical option here.

 

Best wishes,

Peter

The LearnEnglish Team

I have a question, please.........
Can we use 'could know' in the following sentence,
- He wishes he .......... where he put the money, he misplaced.
Or is it just. 'knew' ?

Hello ExistentialAwareness,

Grammatically it is possible, but we would not use it as the question is not whether it is possible to know or not but whether the person in question actually does know or does not. We might talk about the possibility of knowing in the context of, for example, theoretical physics, where there are possible limits to the extent of our ability to observe phenomena, but this does not apply to your example.

 

Best wishes,

Peter

The LearnEnglish Team

#Peter M
Thank you very much!

Hey there,

For a question such as:

"When can you start?"

Is that considered a request or an offer?

Cheers,

Jordan

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