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

  • 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.
 
Respected Sir,
i wanna draw your attention to above your illustrations, as you are giving it that we can make sentences by the help of CAN that what is possible or impossible. cannot we use COULD for this purpose ?
like,1. you are waiting for her, she could come.
it is getting dark, you could hurt yourself.
Thanks.

Hi Alien Mars

Thanks for your comment. There are always lots of different ways to express the same thing in English - that's part of the fun! 

I am an English teacher but do not consider myself an expert on English grammar. I think that the ideas used to describe when we use particular modal verbs are simplified to make things easier for learners. When I have taught this in the past, I have told my students that can and can't are used to say that something is possible or impossible and that could/couldn't might/might not may /may not are used to describe whether something is probable or improbable (whether or not I think something is likely). 

For example:

Alice is singing in a concert tonight. She can sing really well.

Do you think she will sing her own songs? (songs that she wrote)

I don't know, she could do, or she might sing covers. (songs written by others)

I realise that it is more complicated than that and these are simplifications but I hope that they help learners.

Thanks

Jack Radford

The LearnEnglish Team

hello sir,
i am always confused in using 'be' as in can/can be ,may /may be....
cud you help me in this regard .
thanks
mito

Hello Mito,
One basic rule is that after a model verb (like can, may, will, must etc.) we use 'be' if the next word is an adjective, adverb or noun. For example, 'He can be very funny.' 'She may be late to work today.' 'It will be faster to walk.' 'They must be the new neighbours.'
If the next word is a verb then we don't use 'be'. For example, 'You can speak English very well.' 'I will see you later.' One exception is with passive forms, which take the verb 'to be' as part of their form. For example, 'My pet mice must be fed regularly.'
I hope that helps.
Best wishes,
Adam
The LearnEnglish Team

hello every body!
i have a difficulty to make difference between must and can in giving obligations
i want to know the present negative form of must and the past form of must
thanks a lots
 

 Hi amineahmed,
The present negative form of must is must not (mustn't). When talking about the past, must becomes 'had to.' (e.g. 'I had to wake up very early when I was young.')
Can is not used to talk about obligations. Can is used to talk about permission and ability, among other things.
I hope this helps.
-Erik
The LearnEnglish Team

thanks ,Jack, if you are not expert in Englsih right now but it is near to be an expert in English at he future

This  article really helped me in distingushing between 'can' & 'must '. Additionally   it gave an insight about proper use of  'can'.

Thank you for very useful information.

Dear Sirs,
I think there is a mistake in the next sentence: Can I carry bag that for you?
Thank you for teaching
 

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