Do you know how to use must, might, may, could and can't to say how certain you are about a possibility?

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

Modals – deduction (present): 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

Modals – deduction (present): Grammar test 2

Language level

Intermediate: B1