You are here


Level: beginner


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


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



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.


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


Probability 2


Probability 3


Probability 4


Probability 5




Good morning!

Reading this article, I find myself a little surprised as I always assumed a different pattern of usage for "may", "might" and "might have" because I basically would tend to think about how a sentence sounds more than how much it adheres to grammar rules. I know it's a bad, bad habit and that's why I tend to come to the basics from time to time, although being in the upper-intermediate/advanced level. This is most likely a wrong mindset coming from (another) bad habit of trying to search a direct translation of tenses between my native language and English so a big THANK YOU for this great article.

Hey there
so I'd like asking
what is the difference between those sentencesq
could be very cold in winter.
It can be very cold in winter.
and please point out any mistakes in the question text

Hello abdullah,

You can find an explanation of 'can' and 'could' on our can, could and could have page, and be sure to look at the other pages in the Modal verbs section as well.

Best regards,
The LearnEnglish Team


I need your help in understanding the difference between "must" and "will" when we want to express a deduction. What's the difference between them? Is one stronger than the other? Are they used to express different nuances?

For example: The phone's ringing. That must be Dad...or that'll be dad?

Thank you for your insights.

Hello Knightrider,

The difference is quite subtle. We generally use 'must' when we are making a logical deduction which has a strong basis. For example, we would say 'That must be Dad' if we had been waiting for a phone call from Dad for a while and it was overdue. We would use 'will', on the other hand, for something that is normal, expected or typical. For example, we would say 'That will be Dad' if the phone rings and we know that Dad always phones at this time on this day. In other words, 'must' expresses a logical deduction based on some kind of evidence, whereas 'will' expresses an expectation based on the normal pattern of things.

Of course, these are subjective assessments rather than objective rules of what is correct and what is incorrect. This means that a given speaker can choose which form is most appropriate for a given situation, depending on how they see that situation.

I hope that helps to clarify it for you.

Best wishes,



The LearnEnglish Team

A thorough illustration, as always. Now I got it. Thank you so much Peter.


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,
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,
The LearnEnglish Team