Modal verbs of deduction – must, may, might, could, can’t

Exercise 1

Choose all the correct modal verbs of deduction for each gap below. In some sentences there are TWO possible correct answers.

Exercises: 1 2 3

Modal verbs of deduction – Grammar chart

Modal verbs of deduction – must, might, could, can’t

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May, might

He’s more than 2 meters tall. He might be a basketball player. (=perhaps he is)
He says Betty is his friend, but I think she may be his girlfriend.

We use may not or might not to talk about things that are possibly not true, but we don’t know for sure.

You should call her. She might not know where you are. (=perhaps she doesn’t know)

Don’t use can for deduction

We don’t use can as a modal of deduction.

He can be at home now.
He might/may be at home now.

Must, can’t

We use must when we are sure, or quite sure, that something is true.

You must be tired after the long journey. (=I’m sure you are tired)
I’m sure I had the keys when I left. They must be in the car.

But we use can’t (NOT mustn’t) when we are sure, or quite sure, that something is not true.

We’ve been walking for hours. It mustn’t be far from here.
We’ve been walking for hours. It can’t be far from here.
They’ve lived here only for a couple of months. They can’t know many people.

+ be + -ing

After may, might, must or can’t, we can use be + -ing, when we are talking about actions in progress.

They’ve gone to Ibiza, and right now, they must be having a great time.
Call him. He might be waiting for us.

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