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

Hello Kirk,
Thanks for your reply.

The context was that a patient was discussing possible causes of her having the IBS with her doctor. So she asked the doctor whether starting a stressful job might have triggered her bowel problems.
That is why her question was vague to me " could the new job has something to do with getting IBS?"

I guess now, because of your response, this sentence is not appropriate to be used in an official English speaking test, am I correct?

Hi Hopefinder,

I'd want to see the full context, but as you've explained things, that question sounds appropriate to me, but 'has' should be 'have'.

All the best,
Kirk
The LearnEnglish Team

Thanks Kirk for your help.
I really appreciate it.

Hello Learn English team

Could you kindly explain this sentence for me: "could my new job has something to do with getting IBS" , I was not lucky to find its meaning online , it looks grammatically strange for me as well?

Another Question please if I may, can I use such a sentence in an official speaking test or it is only considered as informal or slang language?

Big thanks in advance

Hi Hopefinder,

You're right in thinking that that question is not grammatical. It should be 'Could my new job have something to do with ...'. I can't say for sure without knowing the context, but IBS could mean irritable bowel syndrome.

All the best,
Kirk
The LearnEnglish Team

Hi, I hope you can help me. In this sentence: "I wanted only to open your eyes to the world we could create together", what does "could" mean? Does it refer to the past or is it a request in the present?

Hi Chris,

'Could' here describes possibility. There is an implied conditional form here: ...the world we could create together (if you agreed / if you were brave enough / if you wanted to / if you came with me).

 

Peter

The LearnEnglish Team

So, 'could' in this sentence does not refer to an action in the past? I have doubts because in this sentence the verb 'sought' is used, which is the past of seek. And that's why I thought the whole sentence was in the past.

Hello again Chris,

No, the meaning here is not past, but rather hypothetical. Could sometimes refers to past time (when describing ability, for example) but it can also refer to present or future time (possibility, probability and so on).

In your sentence we have an implied condition, making the sentence a hypothetical construction. We would need could have if we wanted to refer to a possibility in the past.

 

Peter

The LearnEnglish Team

Thank you very much for answering and helping me.

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