Grammar Lessons: Modals of Deduction

Modals of Deduction

Modals of Deduction

The English modal verbs “must”, “have to”,”may”, “might” “can’t” and “couldn’t” are used to express deduction and contention. Modal verbs are used to state how sure the speaker is about something.

Must (Certainty about the Present)

We use must when we feel sure that something is true because there’s very strong evidence.

  1. He must be around here because his car is parked there
  2. You are pilot, that must be interesting
  3. You have worked all day, you must be tired
  4. He has an expensive car, he must have some money
  5. He must live near here because he comes to work  on  foot.
  6. She’s not here. She must be in the kitchen.
  7. Her son is at university so she must be at least 40
  8. Carla works every day from 9 AM to 5 PM so she must be at work
  9. She isn’t answering the phone, she must be out
  10. He drives an expensive car, he must have a good job

Must (Certainty about the Past)

W use must have and couldn’t have plus the past participle of the verb to draw a conclusion abour what happened in the past

  • Sheila got a tan. She must have spent a lot of time in the sun lately.

Might, May and Could

We use mightmay or could to say that we think something is possible but we’re not sure.

  1. I heard a noise, there might be a cat on the roof
  2.  He might be  in his bedroom
  3. He might be in the Gym,  sometimes he goes there
  4. Don’t eat it! It could be poisoned!
  5. Jerry is very tall so he might be good at basketball.
  6. She is busy, she might not be able to come tonight


We use can’t when we feel sure something is not true.

  1. He can’t be dead, I just talked to him on the phone
  2. It can’t be a mechanical problem, the car is new
  3. That can’t  be James, James wears glasses
  4. My wallet can’t be in my backpack, I already checked there
  5. She can’t be a mother, she’s only 14!
  6. He can’t be in prison, I saw him yesterday in a pub.
  7. They can’t be Spanish, they’re speaking Portuguese

Modals of Deduction Exercises

Exercise #1

Modals of Deduction: Must, Might and Can’t

Choose Must, Might and Can't

Exercise #2

A: Hey, what is the matter with you?

B: Well, I have to tell you something and I think you _________________ like it.

A: Come on! Tell me what it is. It _________________ be that bad.

B: I don’t know. I’m afraid you _________________ react badly.

A: Then I’m sure it _________________ be serious. Please, tell me.

B: I saw Lindsey holding hands with another man.

A: What?

B: Please, I know you 10 __________________ be upset right now, but…

A: Dude, Lindsey and I broke up more than a year ago. Didn’t you know?

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