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

Thanks Peter,
Could you please provide an example with context for 'May' to further elaborate its use for permission.
Thank you once again.

Hi,
Look at the sentence 'I consoled myself with the thought that things could be much worse'.
In this sentence how can we know 'could' is used either as past form of 'can' or 'could' is used for past possibility. we use 'can' for general possibility and 'could' for possibility in a single occasion. So when we want to say this in a past sentence like above, how can we know it is a general possibility or a possibility in a single situation. In the past sentences we use preterite form of 'can'. So I get confused it is a general possibility or a possibility in a single situation.

Hello jitu_jaga,

The modal verb does not carry a marker for this within it so we use the context to inform us. If the context is not clear then it is ambiguous, but this would rarely matter.

For example, the meaning of your sentence is quite clear, I think. The speaker is looking at a bad situation and consoling themselves with the thought that something worse is possible. It may or may not be obvious from the context whether the worse possibility is something specific (my car is not working but it could be worse - my car could have exploded) or general (my car is not working but it could be worse - I could have lost my job, got sick or suffered some family tragedy). It really does not matter, however; what is important is the idea that things are not as bad as they could be, and that the person's ill-fortune is not so terrible when considered in the right way.

 

Peter

The LearnEnglish Team

Thank you Peter. You always provide good explanations. Have a nice day.

Hi,
We use may/might/could for possibility and may/might/could have for past possibility. But we don't use 'would' for possibility. But sometimes, I find sentence like ' You would know, Sachin Tendulkar is a great batsman'. I think here 'would' is used for speculation if I am not wrong.

In this sense, if we write sentences like
It may/might/could rain tomorrow, could we write 'It would rain tomorrow' or 'I would marry next month'?. If not then what would be its meaning? I don't understand how to use use 'would' for future and past speculation.Could you Please explain it clearly.

Hello jitu_jaga,

The sentence about Sachin Tendulkar you mention doesn't sound right to me, at least out of context. In other words, perhaps in a specific context it would make sense, but out of context it does not.

Your other sentences with 'would' to talk about possibility (rain or getting married) are also not standard. At least in British or American English, 'would' isn't used to speak about possibility in this way. It can be used within a conditional structure to speak about a possibility, but that is a different structure, which is clearly indicated in most cases with an 'if' clause.

All the best,
Kirk
The LearnEnglish Team

Thank you Kirk, have a nice day.

Sir, As We use must+have+ed form of verbs to talk about deduction and probability in the past and use could or can+not+have+third of verbs to talk about the same in negative in the past right ?

But is there a structure in English like this must+not+have+ed form of verbs to talk about past negative deduction and probability or to talk about something else?

Hi SonuKumar,

In answer to your first question, yes, that is correct.

'She must have gone home' means the speaker has good reasons to believe she went home, or that it is the only logical explanation they have at hand to explain a situation.

'She can't have gone home' means the speaker has reasons to believe that it is impossible that she went home.

'She must not have gone home' is not as strong. It means the speaker is making a supposition -- they think she probably did not go home, but don't have strong evidence for this.

I hope that makes it clear.

All the best,
Kirk
The LearnEnglish Team

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