Modals of Deduction (IELTS, TOEFL, YDS Practice) – B2 Grammar Test
This B2 grammar test focuses on modals of deduction, which are used to express certainty, probability, and impossibility based on evidence.
Choose the correct answer.
RESULTS
#1. The lights are off and nobody is answering the phone. They ___ be at home.
#2. She has been studying all night. She ___ be exhausted.
#3. I’m not sure where Tom is. He ___ be at the gym.
#4. That restaurant ___ be very good. It’s always full.
#5. He just ate a huge meal. He ___ be hungry now.
#6. She didn’t answer my message. She ___ have seen it yet.
#7. The car keys aren’t here. You ___ have left them at the office.
#8. He looks very confident. He ___ know the answer.
#9. It’s possible that the train is delayed. It ___ arrive late.
#10. She ___ be the manager. She looks far too young.
#11. Someone is knocking at the door. It ___ be the courier.
#12. He didn’t attend the meeting. He ___ have forgotten about it.
#13. The ground is wet. It ___ have rained last night.
#14. This answer is completely wrong. You ___ have understood the question.
#15. She isn’t answering her phone. She ___ be driving.
✅ Answer Key with VERY DETAILED EXPLANATIONS
🧠 B2 Modals of Deduction – Exam Logic
🔑 Core Concept (Read First)
Modals of deduction express how certain the speaker is, based on evidence.
| Modal | Meaning |
|---|---|
| must | strong logical certainty |
| might / may | possibility (50% or less) |
| can’t | logical impossibility |
These modals are not about rules or permission, but about logical inference.
1. can’t
The evidence strongly suggests they are not at home. If the lights are off and nobody answers, being at home is logically impossible.
❌ must → certainty in the opposite direction
❌ might → too weak for the evidence
📌 Typical YDS deduction question
2. must
Studying all night is strong evidence of exhaustion. The speaker is almost certain.
❌ might → uncertainty not justified
❌ can’t → contradicts evidence
📌 IELTS Speaking inference
3. might
The speaker is unsure and only suggests a possibility.
❌ must → too certain
❌ can’t → no evidence of impossibility
📌 TOEFL listening-style reasoning
4. must
A restaurant that is always full is logically very good.
❌ might → weak conclusion
❌ can’t → illogical
📌 Common IELTS inference pattern
5. can’t
Someone who has just eaten a large meal is logically not hungry.
❌ must → opposite meaning
❌ might → contradicts strong evidence
📌 YDS cause–effect logic
6. can’t
If she had seen the message, she would probably have replied. This suggests impossibility.
❌ must → certainty without proof
❌ might not → weaker than required
📌 Advanced past deduction
7. must
The absence of the keys strongly suggests they were left elsewhere.
❌ can’t → illogical
❌ would → conditional, not deduction
📌 TOEFL past inference
8. must
Confidence is strong evidence of knowledge.
❌ can’t → contradiction
❌ might not → unlikely
📌 IELTS Speaking evaluation language
9. might
A delay is possible but not certain.
❌ must → too strong
❌ can’t → no impossibility
📌 TOEFL uncertainty marking
10. can’t
Looking far too young makes the conclusion logically impossible.
❌ must → opposite conclusion
❌ might → uncertainty not appropriate
📌 YDS appearance-based deduction
11. must
Knocking at the door is strong evidence that the courier has arrived.
❌ can’t → illogical
❌ would → hypothetical
📌 IELTS real-life inference
12. must
Forgetting is the most logical explanation for missing the meeting.
❌ can’t → no contradiction
❌ will → future prediction
📌 TOEFL reasoning tasks
13. must
Wet ground strongly suggests rain occurred.
❌ can’t → contradicts evidence
❌ might not → illogical
📌 Science-related deduction
14. can’t
A completely wrong answer suggests misunderstanding.
❌ must → wrong direction
❌ might → too weak
📌 YDS inference elimination
15. might
Driving is a possible explanation, but not certain.
❌ must → too strong
❌ can’t → no evidence
📌 IELTS everyday deduction
🧠 B2 Exam Survival Summary
Use must when evidence is strong
Use might / may when evidence is uncertain
Use can’t when something is logically impossible
At B2 level, exams test reasoning strength, not grammar labels.
