Deduction Modals Exercises
B2 Level
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For past deductions, add "have" + past participle after the modal: "He must have left early" (I am almost sure he did), "They can't have seen us" (it was impossible), "She might have taken the wrong train" (it is possible). The level of certainty goes: "must" (strongest positive) → "may/might/could" (possible) → "can't/couldn't" (strongest negative). A common mistake is using "mustn't" for negative deduction — mustn't means prohibition (you are not allowed), not impossibility. For negative deduction, always use "can't" or "couldn't": "It can't be true" (not "It mustn't be true"). This distinction is heavily tested in Cambridge B2 First exams.
Quick Rule
must / can't / might / could + be (present) | must / can't / might / could + have + past participle (past)
- 1.She must be tired — she has been working all day. (strong positive deduction)
- 2.He can't be a doctor — he's only sixteen! (impossibility)
- 3.They might be lost — they should have arrived by now. (possibility)
- 4.You must have left your keys at the office. (past deduction — almost certain)
- 5.She couldn't have known about the surprise party. (past impossibility)
All 20 questions
Complete with the correct modal for making deductions about present or past situations. Use evidence to make logical conclusions - think about certainty levels (very sure, impossible, or just possible).
The lights are all off. Everyone _____ asleep.
Complete with must be, can't be, might be, or could be.
That _____ John at the door. He's in Paris this week.
Complete with must be, can't be, might be, or could be.
She's not answering her phone. She _____ in a meeting.
Complete with must be, can't be, might be, or could be.
He's wearing a winter coat in July. He _____ very cold.
Complete with must be, can't be, might be, or could be.
That _____ her car. She doesn't know how to drive.
Complete with must be, can't be, might be, or could be.
The door is locked and all the lights are off. They _____ already left for work.
Complete with must have, might have, or could have.
I heard a noise upstairs. It _____ the cat or the wind.
Complete with must be, can't be, might be, or could be.
She's smiling and laughing. She _____ happy about something.
Complete with must be, can't be, might be, or could be.
That _____ the right address. There's no building with that number on this street.
Complete with must be, can't be, might be, or could be.
The train is two hours late and hasn't moved. There _____ a serious problem on the line.
Complete with must be, can't be, might be, or could be.
That _____ real gold. It was so cheap!
Complete with must be, can't be, might be, or could be.
He looks exhausted. He _____ working too hard lately.
Complete with must be, can't be, might be, or could be.
I'm not sure where Tom is. He _____ in the library or the cafeteria.
Complete with must be, can't be, might be, or could be.
That _____ the teacher. She's wearing our school uniform - she must be a student.
Complete with must be, can't be, might be, or could be.
The shop is closed, dark inside, and there's a 'Back Tomorrow' sign. They _____ already gone home.
Complete with must have, might have, or could have.
She speaks perfect English with no accent at all. She _____ a native speaker.
Complete with must be, can't be, might be, or could be.
That _____ right. I checked it three times.
Complete with must be, can't be, might be, or could be.
Someone is knocking. It _____ the delivery person or our neighbour.
Complete with must be, can't be, might be, or could be.
That _____ his final answer. He never decides things that quickly.
Complete with must be, can't be, might be, or could be.
You've been studying for hours. You _____ tired now.
Complete with must be, can't be, might be, or could be.
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