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

Hello Mr. Kirk. Greetings.
Surely i understand that (should/would/must) - don't have the past forms. But as you have said they
can be used as in the past as and in other tenses. I mean the verbs: (could/should/would/must) don't have some specific time. We use them whether in the past or in the present or future, to express FACT, ASSERTION.
If we add to them the perfect-aspect (could/should/would/must have) - they mean the "imposible condition". It's used to describe a situation that didn't happen, and to imagine the result of this situation. Whether in the past or present or future to express SUPPOSITION, HYPOTHETICAL.

Hello rewand,

I'm afraid you're still trying to oversimplify the use here and the rules you are trying to impose on the language do not fit the way it is used.

'He could stop smoking' - a future possibility

'He could have stopped smoking' - a possibility in the past; without further information we do not know whether or not he stopped; we are simply stating that it is not impossible

Modality is very much context-dependent and describes how the speaker sees a particular action or state.

Best wishes,

Peter

The LearnEnglish Team

Hello sir
I confused sir how can i use might in the future in sometimes

Hello shah Muzamil,

Have you seen our page on may and might? Please give us an example of what you mean. For more guidelines on how to write a comment, please see the question on the comment section on our Frequently asked questions page.

All the best,
Kirk
The LearnEnglish Team

Can the (should/would/must) - use in the past? Or i should use in the past only (should/would/must have)? Thanks)

Hello rewand,

I'm afraid I can't answer this question completely, as it's quite complex and would take too long to explain. These modals definitely don't have past forms, but can be used to express past meanings (e.g. in reported speech, 'He told me I should study more'), among other uses. I'd suggest studying and practising each modal verb in some depth – in that way you'll come across some of these uses.

Best wishes,
Kirk
The LearnEnglish Team

Hello guys. Greetings to the England. I have searched for the explanation of (could have) and i guess i have it.
Could - this is the FACT which says that (something) was able to do something in the past.
Could have - this is the SUPPOSITION which says that something could have happened in the past, but it didn't happen.
The first sentence: When i was at school i could run quickly.(I was able to run quickly)
The second sentence: When i was at school i could have run quickly.(But i didn't) - SUPPOSITION.
1.Could have = 2.(would can) - the second isn't use i guess, but it helps to understand the first.

Hello rewand,

Both 'could' and 'could have' have multiple uses, as shown on this page. While there are core notions behind each, I would advise against oversimplifying in this way. Trying to find an overly simple rule results in a mass of exceptions and confusion, in my experience.

Best wishes,

Peter

The LearnEnglish Team

I can understand the meaning of could have.....but i didn't understand the use of could have been.....??? Or its meaning....kindly guide about that.....

He could have been prime minister now, if he had not decided to leave politics.

What's "could have been" showing/explaining here........because word "been" always makes me confuse....advice me on that....

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