Modals of Deduction Exercises
Do more with this exercise
Use evidence to say how sure you are
Use must when the evidence makes something very likely, might when it is possible but uncertain, and can't when the evidence makes it impossible. For past deductions, add have + past participle.
- Strong conclusion:
- The lights are on. Someone must be home. The evidence strongly supports this conclusion.
- Possibility:
- She might be at the library. It is possible, but I do not know.
- Impossible conclusion:
- He can't be at work; he is sitting next to me. The evidence rules it out.
- Past deduction:
- She must have missed the bus. Use modal + have + past participle for a conclusion about the past.
- Past possibility or impossibility:
- They might have left early. He can't have seen us; he was away. The certainty still comes from the evidence.
Examples
Her coat is here. She must be nearby.
strong conclusion from present evidence
No one answered. They might be out.
one possible explanation
He can't be asleep; he is talking to us.
the evidence makes sleep impossible
The ground is wet. It must have rained last night.
strong conclusion about a past event
I cannot find my keys. I might have left them at work.
possible past explanation
Audio uses a synthetic voice.
Practice exercises
Choose the strength of the deduction
Choose must, might or can't according to the evidence and certainty stated.
1.The café is full and every table is taken. It ___ be popular.
2.I am not sure where Leo is. He ___ be at the gym.
3.Sofia ___ be in Paris now. She is here in the room with us.
4.The cake has disappeared and Max has chocolate on his face. He ___ eaten it.
5.Perhaps Nina ___ missed the email. I don't know yet.
6.Tom ___ seen the concert yesterday. He was in hospital the whole day and the event had no livestream.
Complete the deduction
Use the modal named in the hint. Type all missing words, including have where needed.
Fix the modal form
Replace the incorrect modal phrase with the correct one. Keep the rest of the sentence.
13.Choose the mistake in this sentence.
14.Choose the mistake in this sentence.
15.Choose the mistake in this sentence.
16.Choose the mistake in this sentence.
17.Choose the mistake in this sentence.
18.Choose the mistake in this sentence.
Make careful deductions from evidence
A deduction is a conclusion based on what you can see or know. The modal shows how certain you feel. If the evidence strongly supports an idea, use must. If it is only one possible explanation, use might. If the evidence rules it out, use can't. These forms describe what you conclude, not what someone is required or allowed to do.
For present deductions, the modal is followed by a base verb: “She must be here.” To look back, add have and a past participle: “She must have arrived.” The same pattern works with might and can't. The word have stays in its base form after the modal.
Read the evidence before you choose. Words such as perhaps and not sure point towards possibility; direct contradictions point towards can't. Strong clues support must, though real life rarely gives perfect certainty. Make sure the verb phrase has the right form as well as the right meaning.
Frequently asked questions
What is the difference between must and might for deduction?
Must expresses a strong conclusion based on evidence. Might expresses a possibility that you are not sure about.
Does can't mean impossible here?
Yes. In a deduction, can't means the evidence makes that conclusion impossible or very unlikely: “He can't be at work; he is here.”
How do I make a deduction about the past?
Use must, might or can't + have + past participle: “She must have left,” “She might have left,” or “She can't have left.”
Can could replace might?
Could can also express possibility in many contexts. This lesson uses might consistently for uncertain possibilities so that the contrast with must and can't is clear.
Answer key
1. The café is full and every table is taken. It ___ be popular.
Answer: must
A full café strongly supports the conclusion that it is popular.
2. I am not sure where Leo is. He ___ be at the gym.
Answer: might
The speaker is uncertain, so might shows a possibility.
3. Sofia ___ be in Paris now. She is here in the room with us.
Answer: can't
Being here rules out being in Paris at the same time.
4. The cake has disappeared and Max has chocolate on his face. He ___ eaten it.
Answer: must have
The evidence strongly suggests that Max ate the cake.
5. Perhaps Nina ___ missed the email. I don't know yet.
Answer: might have
Perhaps and I don't know signal an uncertain past possibility.
6. Tom ___ seen the concert yesterday. He was in hospital the whole day and the event had no livestream.
Answer: can't have
The circumstances rule out his seeing the concert.
7. There was a storm here last night, and the streets are wet. It ___ last night.
Answer: must have rained
The storm and wet streets strongly support rain; a past deduction uses must have + past participle.
8. I'm not certain. The parcel ___ at the wrong address.
Answer: might have arrived
An uncertain past possibility uses might have + past participle.
9. She ___ asleep now; I can hear her speaking on the phone.
Answer: can't be
The evidence rules it out, so use can't be.
10. I can see someone moving behind the office window. Someone ___ there.
Answer: must be
Seeing a person moving inside strongly supports the conclusion that someone is there.
11. I am unsure. Ben ___ at home today.
Answer: might be
Might be describes a possible present situation.
12. She ___ the meeting yesterday; she was on a flight without internet throughout it.
Answer: can't have attended
A past event ruled out by evidence uses can't have + past participle.
13. The lights are on. Someone must to be home.
Answer: The lights are on. Someone must be home.
A modal takes the base verb without to: must be.
14. I am not certain, but she might is at the station.
Answer: I am not certain, but she might be at the station.
After might, use the base form be.
15. He can't to be at school; he is standing here.
Answer: He can't be at school; he is standing here.
After can't, use the base form without to.
16. The ground is wet. It must has rained last night.
Answer: The ground is wet. It must have rained last night.
A past deduction uses modal + have + past participle.
17. Perhaps she might has left her bag on the train.
Answer: Perhaps she might have left her bag on the train.
Use might have + past participle for a possible past event.
18. He can't have saw the film at the cinema last weekend; the cinema was closed all weekend.
Answer: He can't have seen the film at the cinema last weekend; the cinema was closed all weekend.
After modal + have, use a past participle: seen.