Look at these examples to see how must, might, may, could and can't can be used.
That must be the main entrance. I can see people queuing to get in.
I've lost my keys. They might be at work or they could be in the car.
You can't be bored already! You've only been here five minutes.
Try this exercise to test your grammar.
- Grammar test 1
Read the explanation to learn more.
Grammar explanation
We can use modal verbs for deduction – guessing if something is true using the available information. The modal verb we choose shows how certain we are about the possibility. This page focuses on making deductions about the present or future.
must
We use must when we feel sure that something is true or it's the only realistic possibility.
This must be her house. I can see her car in the garage.
He must live near here because he always walks to work.
Come inside and get warm. You must be freezing out there!
might, may, could
We use might, may or could to say that we think something is possible but we're not sure.
She's not here yet. She might be stuck in traffic.
He's not answering. He could be in class.
We regret to inform you that some services may be delayed due to the bad weather.
They all have the same meaning, but may is more formal than might and could.
can't
We use can't when we feel sure that something is not possible.
It can't be far now. We've been driving for hours.
She can't know about the complaint. She's promoted him to team leader.
It can't be easy for him, looking after three kids on his own.
Note that these verbs, like all modal verbs, are followed by an infinitive without to.
Do this exercise to test your grammar again.
- Grammar test 2
Hello!
Could you please help me with this issue:
If I, for example has fixed my sink, could I say "It has to be better now" or "It must be better" is the only correct variant? As I understand, we never use "have to" for deductions, but I'm not certain.
I very appreciate your work and thank you very much for answering this post!!!!!
Hello howtosay_,
You can use either form for deductions. Must is more common, but it's possible to use have to when you want to express a strong conviction:
Peter
The LearnEnglish Team
Hello. Could you please help me? I think both give suitable meaning.
- He (must be - can't be) cold. He isn't wearing a jacket.
Thank you.
Hello Ahmed Imam,
Both are possible but show the speaker has a different perception. 'He must be cold' means the speaker thinks the man is cold; 'He can't be cold' means the speaker thinks he is not cold.
Does that make sense?
All the best,
Kirk
The LearnEnglish Team
Hello Oliver Goldwyn,
In this context you are speculating about the future so the correct choice is might.
Peter
The LearnEnglish Team
Hello BobMux,
To be honest, neither of these sound natural to me, but if I were to use one of them, I'd use 1. If I don't know whether they are sleeping or not, but think that they probably are, I'd say 'Don't call them now. They're probably sleeping' (or perhaps 'They might be sleeping').
I'd use 'they must be sleeping' if, for example, I called them but they didn't answer the phone.
I can't think of a situation when I'd use 'can' here.
All the best,
Kirk
The LearnEnglish Team