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Probability

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.

Probability 1

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Comments

Hi Peter M. I see you using 'could in your comments when replying user questions. Is 'could' used to make a suggestion and means be able to?

We can use the definite article in several ways. When you say 'the bus' it could mean a particular bus (Look - the bus is coming!) or it could have a general meaning and refer to the means of transportation (I prefer the bus to the train).

Second, can I say 'it may mean...'/'it may have'...? If so, is there any difference of meaning?

Hello The LearnEnglish Team!
Could you please help me understand better the difference between "can" and "might, may and could" when we are using them to express possibility?

Hello BobMux,

This is a very general question which requires contextualised examples. Perhaps you can provide an example sentence to illustrate what you mean. This will help to clarify your question and also ensure that our explanation is clear for you.

 

Peter

The LearnEnglish Team

Hello there!
I would like to know the difference in meaning of these two sentences:
It can be dangerous to cycle in the city.
It could/may be dangerous to cycle in the city.

Hello BobMux,

The sentence with 'can' speaks more about cycling in the city in general, i.e. at any time, in any situation, for any person. The sentences with 'could' or 'may' are more often used to speak about a more specific hypothetical time or situation in the future.

For example, let's say a friend of ours was cycling in the city and had an accident. We could say the first sentence as a kind of comment on how dangerous it is to cycle in the city after this specific event. The second sentence wouldn't work well in this situation -- it's more for a time we're thinking of that could happen in the future, for example, if we're thinking about whether we should take our children cycling in the city tomorrow.

I hope this helps you make more sense of it.

All the best,

Kirk

The LearnEnglish Team

Hello Kirk,
It was rather useful your explanation and thanks a lot. But i am still a bit confused. I would be really happy if you were able to help me understand better modal verbs:
In a book it is said that the modal verbs "might", "may" and could are used to express both possibilty and make a guess. This words is given " this rush might/could/may be a symptom of something more serious". So here is it possibility or making a guess?
And how can i distinguesh between possibilty and making a guess?

Hello BobMux,

Modal verbs are used in a number of ways, which can make understanding them a little challenging. It's really difficult to summarise these uses in a few posts here, but I will try to help you here. Please know, though, that you'll probably need to spend some time noticing them in different contexts (ideally as you read text or listen to speech) to really understand them well.

I'm not sure exactly what the difference between 'possibility' and 'a guess' are -- these can be defined in different ways. But generally speaking, I'd say 'may' and 'might' are expressions of the speaker's uncertainty about something. If we say 'The bus may be late', we are guessing but don't really know. In a way, this is also saying that it's possible for the bus to be late, though.

'could' can express the same idea of the speaker's uncertainty. Being related to 'can', it can also express the idea of potential, but again, in this context, I'm not that really means anything too different.

I hope this helps you.

All the best,

Kirk

The LearnEnglish Team

Dear teahcers,

1- Why can't we use " can have " to make guesses about the past like may have, might have or could have ?

2- Why can't we use " couldn't " to say that something is impossible like " can't " ?

Hello ahmed16,

I wish that it were a bit more logical, but I'm afraid this is just the way that English has developed as people have been speaking it over the last several centuries. There are some technical analyses of modal verbs that can help understand how they work a bit better, but I'm afraid they require a bit of study to make sense of and are well beyond the scope of what we do here.

Best wishes,

Kirk

The LearnEnglish Team

ok
Do you mean that it is a language and its rules must be adhered to, even if what I am saying is relatively true?

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