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.

 

Exercise

Comments

Does "could" mean "can probably" here? Or maybe a hypothetical?

The comentator could have said "the game is underway".
I could have said "I will do my best".

Hello akatsuki,

These look like they refer to the past possibility to me, though it's hard to say without knowing the context. Context is key when it comes to understanding verb forms. 

Best wishes,
Kirk
The LearnEnglish Team

Hi
What does "arrived" representing in could have structure?
Also Above question
Gramatically correct?

Hi Muhammad Salik,

You can find the meanings of individual words like 'arrived' by using the Cambridge Dictionaries Online tool on the right of the page. Simply type the word into the window and click 'Look it up!' to get a definition, examples, synonyms, pronunciation and more. It's a great tool.

Your question is not grammatically correct. The best way to phrase it would be:

What does "arrived" mean in the 'could have' structure in the example above?

Have you tried our section 'Elementary Podcasts'? I think they may be very helpful for you.

Best wishes,

Peter

The LearnEnglish Team

hi,
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?
regards,
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,

Peter

The LearnEnglish Team

Hi,
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,

 

Peter

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

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