Level: beginner

Possibility

We use may, might and could to say that something is possible, but not certain:

They may come by car. (= Maybe they will come by car.)
They might be at home. (= Maybe they are at home.)
If we don't hurry, we could be late. (= Maybe we will be late.)

We use can to make general statements about what is possible:

It can be very cold here in winter. (= It is sometimes very cold here in winter.)
You can easily get lost in this town. (= People often get lost in this town.)

Be careful!

We do not use can to talk about specific events:

A: Where's John?
B: I'm not sure. He may/might/could be 
(NOT can) in his office.

Notice the difference in meaning between can and may/might/could:

That dog can be dangerous.
(= Sometimes that dog is dangerous. I know.)

That dog may/might/could be dangerous.
(= Perhaps that dog is dangerous. I don't know.)

can and may/might/could

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Level: intermediate

We use may have, might have or could have to make guesses about the past:

I haven't received your letter. It may have got lost in the post.
It's ten o'clock. They might have arrived by now.
Where are they? They could have got lost.

We use could to make general statements about the past:

It could be very cold there in winter. (= It was sometimes very cold there in winter.)
You could easily get lost in that town. (= People often got lost in that town.)

could and could have

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Impossibility

Level: beginner

We use can't or cannot to say that something is impossible:

That can't be true.
You cannot be serious.

Level: intermediate

We use can't have or couldn't have to say that a past event was impossible:

They know the way here. They can't have got lost!
If Jones was at work until six, he couldn't have done the murder.

Certainty

Level: beginner

We use must to show we are sure something is true and we have reasons for our belief:

It's getting dark. It must be quite late.
You haven’t eaten all day. You must be hungry.

We use should to suggest something is true and we have reasons for our suggestion:

Ask Miranda. She should know.
It's nearly six o'clock. They should arrive soon.

Level: intermediate

We use must have and should have for the past:

They hadn't eaten all day. They must have been hungry.
You look happy. You must have heard the good news.
It's nearly eleven o'clock. They should have arrived by now.

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Comments

Hello jitu_jaga,

'Would' is not used for future possibility without some kind of condition: Knowing out luck, it would rain tomorrow if we went to the beach. 

We do not use 'would' for future possibility in other cases, however.

 

Best wishes,

Peter

The LearnEnglish Team 

Hello,
I am Wondering whether one can use sentences like "It could/may/might have not happened"? Or " It could not/may not/might not have happened"? for negation of possibilities in the past, which also are possibilities and not happened?
Thanks in advance

Hello Seyyed,

The negation can be put in either position with no change in the meaning:

She might/may not have seen him.

She might/may have not seen him.

Both these sentences mean it is possible that she did not see him.

 

Note that 'could' is different. Here the position of the negation changes the meaning:

She could not have seen him. [is is impossible that she saw him]

She might/may have not seen him. [it is possible that she did not see him - the same meaning as above]

 

Best wishes,

Peter

The LearnEnglish Team

Sir, I think He must be sleeping, It's for present, But for past, Should I use this-
I thought He must have been sleeping yesterday ?

Hello SonuKumar,

I'd probably just say 'I thought he was sleeping'. 'I thought' already indicates supposition. Or you could just say 'He must have been sleeping', which indicates supposition. The two forms together would mean you are emphasising the act of making a supposition about him sleeping.

All the best,
Kirk
The LearnEnglish Team

what are the usages of 'Must, must be, and must have been' please help me understand with at least one example for each ?

Hi Kirk
Thank you for answering my previous question . Please I have one more query.
I would go to the cinema , if I have the time.
Is the above sentence correct or should I say I would go to the cinema if I had the time.
Many thanks for your help

Hello sumanasc,

We would use 'had' here. Conditional forms are either about likely/possible events or unlikely/impossible events and we do not mix the two in one sentence. Therefore in your sentence we would either use 'will... have' (likely) or 'would... had' (unlikely).

 

Best wishes,

Peter

The LearnEnglish Team

Hi Kirk
Can you please tell me whether the sentence under modal verb " I could help you , if I find my car " is correct .
Many thanks

Hello sumanasc,

You could probably hear some people say 'I could help you if I find my car', or perhaps find it in writing, but the grammar is a little bit non-standard. This is because the sentence has one verb ('find') in a first conditional structure and the other verb ('could') in a second conditional structure. Please take a look at our Conditionals 1 page to see what I mean.

The sentence in full first conditional structure would be 'I can help you if I find my car' and in full second conditional structure would be 'I could help you if I found my car'.

All the best,
Kirk
The LearnEnglish Team

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