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,
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

Hi sir,

In this sentence 'You could lose your way in the dark. ' , I can't get the aspect. Could you please explain the context . Because I can't understand the usage of could in the past possibility.

Thanks

Hi TJ,

It's important to remember that modal verbs have multiple uses. One use of 'could' is as the past form of 'can' to describe possibility. It's helpful to compare the two:

When it is foggy people can easily get lost on their way home.

I lived in Scotland as a child and it was often foggy, so people could easily get lost on their way home.

The first sentence describes something that is generally possible (getting lost) in certain situations (when it is foggy). The second sentence describes something that was generally possible (getting lost) in certain situations (when it was foggy).

 

Peter

The LearnEnglish Team

got it, clear. Thanks for the quick reply.

cheers

Hi
If I am sure that I did well in exams ,can I say :"I am sure I passed" ?
or something else

Hello Hamdy Ali,

Yes, that is right. Both 'I'm sure' and 'I'm confident' are common ways to experss this. Good work!

All the best,
Kirk
The LearnEnglish Team

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