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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




Hello sumanasc,

You could probably hear some people say 'I could help you if I find my car', or perhaps find it in writing, but the grammar is a little bit non-standard. This is because the sentence has one verb ('find') in a first conditional structure and the other verb ('could') in a second conditional structure. Please take a look at our Conditionals 1 page to see what I mean.

The sentence in full first conditional structure would be 'I can help you if I find my car' and in full second conditional structure would be 'I could help you if I found my car'.

All the best,
The LearnEnglish Team

Hi there,
I have always tried to learn Modals but I find them really difficult!
We use could have to talk about possibility and about ability.
They could have arrived hours ago( did they arrived or not?)
They could have killed him.( did they kill him or not?)
you said we use could have to talk about something was possible at some time but didn't happen. How can we know if this happened or maybe happened?
thanks to the all team members

Khuder, I'm from Brazil and I'm not 100% sure about what I'll tell you now, but, in my opinion, you need to learn how to use only the modal "Could", as soon as you learn it, you will be able to use it with "have" cause it will sound clearer for you. In your example "They could have arrived", it might be more difficult if you analyse it out of a context for example. Oh, they could have arrived many hours ago, lets prepare something to them... So in this case they "maybe yes/not have arrived many hours ago, it's a possibility but you prefer to prepare something to them...
They could have killed him... Is not 100% of sure that they killed him, maybe yes maybe not, it will rely on an investigation...
I don't know if I helped you but I tried.
Bye bye.

Hello khuder,

Modals have lots of different uses, so it's best to take them in small doses! 'could have' implies that the possibility existed but was not realised, so, for example, in your two examples, they did not arrive hours ago and they did not kill him. If you want to make it clear that something was possible and did happen, most of the time you'd probably just use a past simple form, e.g. 'they arrived hours ago', 'they killed him'.

All the best,
The LearnEnglish Team

Hi there,
I'm always baffled by the 'would'. how to differentiate that would in the sentence is conditional or talking about the possibility ( like might or could )?. Do we need to consider the whole context to differentiate between these two? for instance, this paragraph is talking about the Computer Networking terminology.

" Data link layer protocols add a trailer to the end of each frame. The trailer is used to determine if the frame arrived without error. This process is called error detection and is accomplished by placing a logical or mathematical summary of the bits that comprise the frame in the trailer.

Error detection is added at the data link layer because the signals on the media could be subject to interference, distortion, or loss that would substantially change the bit values that those signals represent."

It would be great if you could help me on this regard.


Namaste Kiran,

'would' and all of the different modal verbs can indeed be difficult to learn to use, as they all have multiple uses is different contexts. 'would' is not used to talk about possibilities in the same way as 'may' and 'might'; rather, it communicates the idea of something unreal (e.g. because it's hypothetical or imaginary).

We don't normally comment on texts from other sources, but I'll try to help you with this one since it's very specific. In the fourth sentence, the 'because' clause is talking about a hypothetical situation, more specifically a situation in which the signal is subject to interference. Since this signal interference situation is hypothetical, the changes in the bit values that would result because of it are also hypothetical. The hypothetical nature of this signaled by 'would'. If we said 'will', it implies more reality than is appropriate for this situation.

Does that help?

All the best,
The LearnEnglish Team

I've come across the phrase "I wouldn't know" and looking it up I' ve found out that it can mean two things:
1)I couldn't say, when you haven't experienced something
2) How am I supposed to know?, when you are not the right person to answer a question/comment.

Is that correct?

Thank you.

Hello Knightrider,

I think that's a good summary. The communicative meaning of the phrase is very much dependent on the context, so it's important to look at how it is used in context, not in isolation.


Best wishes,


The LearnEnglish Team

Hello Peter,

Yes absolutely. Context is all-important to distinguish the two meanings. I just wanted to be sure that I have grasped both senses. Thanks again


How can you differentiate between ability, possibility, probability and obligation in the sentence below?
´´Every person has particular ways to do things that may seem strange to others´´.
Thank you!