The modal verbs are can, could, may, might, mustshall, should, will and would.

The modals are used to show that we believe something is certain, probable or possible:

Possibility:

We use the modals could, might and may to show that something is possible in the future, but not certain:

They might come later. (= Perhaps/Maybe they will come later.)
They may come by car. (= Perhaps/Maybe they will come by car.)
If we don’t hurry we could be late. (= Perhaps/Maybe we will be late)

We use could have, might have and may have to show that something was possible now or at some time in the past:

It’s ten o’clock. They might have arrived now.
They could have arrived hours ago.

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

It can be very cold in winter. (= It is sometimes very cold in winter)
You can easily lose your way in the dark. (= People often lose their way in the dark)

We use the modal could as the past tense of can:

It could be very cold in winter. (= Sometimes it was very cold in winter.)
You could lose your way in the dark. (= People often lost their way in the dark)

Impossibility:

We use the negative can’t or cannot to show that something is impossible:

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

We use couldn’t/could not to talk about the past:

We knew it could not be true.
He was obviously joking. He could not be serious.

Probability:

We use the modal must to show we are sure something to be 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 must 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.

We use the modal should to suggest that something is true or will be true in the future, and to show you have reasons for your suggestion:

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

We use should have to talk about the past:

It's nearly eleven o'clock. They should have arrived by now.

Exercise

Section: 

Comments

if we are talk about the past..- It is nearly eleven o'clock. They should have arrived by now, is right -or- It was nearly eleven o'clock. they should have arrived by now??

Hello Apurva Shah,

If you are speaking of the past, in most contexts you would say 'It was nearly eleven o'clock'. But please note that 'by now' doesn't work in the past, as 'now' refers to the present. Therefore the end of your sentence should be something like 'They should have arrived by then (or: 'by that time')'.

Best wishes,
Kirk
The LearnEnglish Team

if i am not certain about a past event
1.Then which one should i use could have+pp or might have+pp or may have+pp
2.or all mean same and can be used interchangeably.
please explain in the light of the above examples that you have used above

It’s ten o’clock. They might have arrived now.

They could have arrived hours ago.

they may have arrived by now

Hi imran_000,

In the specific context you mention, all three modal verbs structures you list mean the same thing - they can be used interchangeably.

Best wishes,
Kirk
The LearnEnglish Team

thanks for your quick response
can you please explain as where to use may have+pp,might have+pp and could have+pp with some examples all in past possibility.

thanks

Hell oimran_000,

Examples of exactly this are on the page:

We use could have, might have and may have to show that something was possible now or at some time in the past:

It’s ten o’clock. They might have arrived now.
They could have arrived hours ago.

We can use all of these modal verbs interchangeably; all three have the same meaning. If any of these examples are not clear, or if you have any specific questions about them, then please let us know.

Best wishes,

 

Peter

The LearnEnglish Team

thanks peter for helping me to understand modal verbs.

i want to know that if all three may have+pp,might have+pp and could have+pp can be used interchangeabily then why do we use three different modal verbs with pp to express the same meaning....hope u understand my question
thanks

Hi imran_000,

I'm afraid it's difficult to explain why this is - languages evolve over time in an organic manner, and that's just how English has developed. As far as I know, all natural languages have redundant forms.

Best wishes,
Kirk
The LearnEnglish Team

Can I use couldn't for possibility in the second conditional sentence? For example, If I lived in a big city, I couldn't breathe fresh air every morning.

Hello cabronasoon,

Yes, it's perfectly fine to use 'could' in this way.

Best wishes,

 

Peter

The LearnEnglish Team

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