Worksheet on Modals of Deduction for English language learners.

Let's solve the exercise on "Modals of Deduction" step by step. This worksheet focuses on using modal verbs like may, might, could, must, can't, and their past forms (must have, can't have, etc.) to express possibility, probability, certainty, or deduction based on evidence.

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🔹 Key Rules Recap:

1. Possibility / Probability (not certain):
- May, might, could → for possible situations
- Example: *She might be watching TV.*

2. Certainty (highly likely):
- Must → positive deduction
- Can’t → negative deduction
- Example: *It must be raining.* / *It can’t be him — he’s in Canada.*

3. Past deductions:
- Use must have + past participle, can’t have + past participle, etc.
- Example: *She must have missed the bus.*

4. Negative sentences:
- Only may not and might not are used with possibility.
- *Could not* is acceptable but less common in this context.

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Now let's go through each sentence and fill in the correct modal verb and verb form.

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✔ Answers with Explanations:

1. That _________ (be) Sean. No one else walks in such a silly way.
→ must be
*Explanation:* The speaker is certain based on behavior. "Sean walks like that" → so it must be him.

2. Take your umbrella. It _________ (start) raining during the day.
→ might start / could start
*Explanation:* Possibility, not certainty. "Might" or "could" are both correct here.

3. Oh no! There’s nobody at the bus stop, the bus _________ already (leave).
→ must have left
*Explanation:* Deduction about the past. Since no one is there, the bus must have already left.

4. Who is Mary talking to? – I don’t know. But she _________ (talk) to the Austrian, because she doesn’t speak German.
→ can’t be talking
*Explanation:* Logical deduction — if she doesn’t speak German, she can’t be speaking to an Austrian.

5. What is he looking for? – I’m not sure, but he _________ (look) for his cell phone.
→ might be looking / could be looking
*Explanation:* A possibility, not a fact. So use might/could be + present continuous.

6. Has John already come? – No. He _________ (stay) longer at work, because he’s so busy these days.
→ must have stayed
*Explanation:* We deduce from his being busy that he must have stayed late.

7. What did you say??? You _________ (joke)! I don’t believe you a single word.
→ must be joking
*Explanation:* Speaker thinks the person is joking based on what was said. Present tense deduction: must be joking.

8. It _________ (be) Dave, who tidied up the room. He never does it.
→ can’t be
*Explanation:* Dave never cleans — so it can’t be him.

9. The book is excellent! It _________ (become) a bestseller soon.
→ must become / will probably become
*But note:* "Must" implies strong belief, but for future predictions, will is more natural. However, since the instruction says "modals of deduction", must is acceptable here as a logical conclusion: *"It must become a bestseller."*

→ must become

10. Where’s your sister? – No idea, she _________ (sit) in the garden and reading a book. Or she _________ (be) chatting in her room.
→ might be sitting / could be sitting
→ might be / could be
*Explanation:* Two possibilities — use might or could for both.

11. I know you’ve given me the keys, but I can’t find them! I _________ (lose) them somewhere.
→ must have lost
*Explanation:* Past deduction. Since they’re missing, the speaker concludes: must have lost them.

12. I’m not sure what to think about what he said. He _________ (be) right. Who knows.
→ might be / could be
*Explanation:* Uncertainty — so use might be or could be.

13. The house is completely dark. They _________ (be) at home.
→ can’t be
*Explanation:* If the house is dark, they can’t be at home.

14. You did very well at the exams. You _________ (study) hard.
→ must have studied
*Explanation:* Good result → logical conclusion: must have studied hard.

15. He looks quite upset. – Yes, he _________ (not/understand) you when you were giving the explanation. – Maybe, I’ll ask him.
→ might not have understood
*Explanation:* Possibility about the past. "He didn’t understand?" → might not have understood.

16. Don’t take that journey, it _________ (be) dangerous for you.
→ might be / could be
*Explanation:* Warning based on possibility — not certain. Use might be or could be.

17. The boss _________ (come) a bit later, he’s talking to some people in his office.
→ must be coming
*Explanation:* Based on current situation ("talking to people"), we deduce he must be coming soon.

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✔ Final Answer List:

| No | Sentence | Correct Answer |
|----|--------|----------------|
| 1 | That ______ (be) Sean. | must be |
| 2 | Take your umbrella. It ______ (start) raining... | might start / could start |
| 3 | ...the bus ______ already (leave). | must have left |
| 4 | ...she ______ (talk) to the Austrian... | can’t be talking |
| 5 | ...he ______ (look) for his cell phone. | might be looking / could be looking |
| 6 | He ______ (stay) longer at work... | must have stayed |
| 7 | You ______ (joke)! | must be joking |
| 8 | It ______ (be) Dave... | can’t be |
| 9 | It ______ (become) a bestseller soon. | must become |
| 10 | she ______ (sit)... Or she ______ (be)... | might be sitting / might be |
| 11 | I ______ (lose) them somewhere. | must have lost |
| 12 | He ______ (be) right. | might be / could be |
| 13 | They ______ (be) at home. | can’t be |
| 14 | You ______ (study) hard. | must have studied |
| 15 | he ______ (not/understand) you... | might not have understood |
| 16 | it ______ (be) dangerous for you. | might be / could be |
| 17 | The boss ______ (come) a bit later... | must be coming |

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📝 Summary Tips:

- Use must for logical conclusions (certainty).
- Use can’t for logical impossibility.
- Use may / might / could for possibility.
- For past deductions, use must have + past participle.
- For negative past deductions, use can’t have + past participle.
- Might not and may not are used for negative possibilities.

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