Modals of Deduction: B2 Exercises

Every answer with the reason behind it. Read the explanation for the ones you got right as well — that is where you find out whether you were right for the right reason.

Multiple choice questions — answers

1. Her coat is still on the hook, so she ___ have gone far. → can't

The negative of a confident deduction is can't have, never mustn't have.

2. There are three missed calls from the same number — it ___ have been urgent. → must

Must have expresses a near-certain conclusion drawn from clear evidence.

3. She never replied. She ___ have received the message at all. → might not

Might not have leaves the possibility open, which is what never replied allows.

4. The parcel ___ have arrived by now; it was dispatched on Monday. → should

Should have expresses an expectation that may or may not have been met.

5. Which sentence means the speaker is nearly certain something did NOT happen? → He can't have seen the email.

Can't have is the negative counterpart of must have; mustn't means prohibited.

6. You ___ told me the deadline had moved. I sat up all night for nothing. → should have

Should have plus a participle is the standard way of criticising something not done.

7. The discrepancy ___ have been a simple rounding error, though we cannot be sure. → could

Could have hedges a claim, presenting one possible explanation among several.

8. They ___ be in a meeting — the door is shut and the blinds are down. → must

Present deduction with strong evidence takes must plus the bare infinitive.

9. Which sentence is INCORRECT? → She mustn't have forgotten.

Mustn't expresses prohibition and cannot be used to deny a deduction.

10. He looks exhausted. He ___ sleeping properly. → can't have been

Can't have been plus -ing denies an ongoing past situation on the basis of present evidence.

11. The keys are not where I left them, so somebody ___ moved them. → must have

Must have is the strong positive conclusion when the evidence leaves no obvious alternative.

12. The difference between 'must have' and 'should have' is that ___. → must have is stronger and reports what you conclude did happen

Must have concludes; should have only expects, and can be followed by a disappointment.

13. They ___ have signed the contract without reading the indemnity clause. → shouldn't

Shouldn't have criticises an action that was in fact carried out.

14. That ___ be Marek at the door — he isn't due back until Friday. → can't

Present negative deduction takes can't plus the bare infinitive.

15. I ___ have left my phone in the taxi, but I honestly cannot remember. → may

May have marks a genuine uncertainty about a completed past action.

16. Which sentence expresses the weakest degree of certainty? → She might have known.

Might have leaves the widest room for the speaker to be wrong.

17. You ___ have bothered — the meeting was cancelled an hour ago. → needn't

Needn't have reports effort that turned out to be unnecessary.

18. The lock is undamaged, so whoever came in ___ have had a key. → must

Undamaged evidence rules out force, leaving the near-certain positive conclusion.

19. It ___ be raining — look at the state of everybody coming in. → must

Must plus a continuous infinitive draws a confident conclusion about right now.

20. Which sentence correctly criticises a past action rather than deducing it? → They ought to have consulted the union.

Ought to have and should have both express that something was the right thing to do.

Fill-in-the-blank questions — answers

1. Her bag is still under the desk, so she ___ have gone home yet. → can't

A confident negative deduction uses this modal rather than the prohibition one.

2. The bins are out already — the neighbours ___ have got up early. → must

Strong evidence for a completed past action takes this modal plus have.

3. He hasn't answered, so he ___ not have seen the message. → may

This modal keeps the possibility genuinely open rather than settling it.

4. The delivery ___ have arrived on Tuesday, but the courier's system says otherwise. → should

This modal expresses an expectation that has apparently been disappointed.

5. You ___ have warned me the road was closed — I lost forty minutes. → should

This modal plus have criticises something that was not done but ought to have been.

6. Nobody ___ have predicted a result like that, so stop blaming yourself. → could

Could have in the negative denies that the ability or possibility ever existed.

7. That ___ be the postman; he came an hour ago. → can't

Present negative deduction uses this modal with a bare infinitive.

8. The alarm is going off, so somebody ___ be in the building. → must

Present positive deduction from clear evidence uses this modal.

9. She ___ have been working here in 2009 — the branch had not opened. → can't

A negative deduction about a past period uses this modal plus have been plus -ing.

10. They ___ have told us the venue had changed, but nobody did. → ought

Ought to have is the near-synonym of should have for criticising an omission.

11. You ___ have gone to all that trouble; there was plenty of food already. → needn't

This modal plus have reports effort that turned out to be unnecessary.

12. It ___ have been him on the platform — I only caught a glimpse. → might

This modal expresses a real but uncertain possibility about the past.

13. The window is broken from the outside, so it ___ have been an accident. → can't

Physical evidence pointing the other way supports a confident negative deduction.

14. They ___ be away — the curtains have not moved in a week. → must

A pattern of evidence over time supports a strong present deduction.

15. I suppose the file ___ have been deleted by mistake rather than deliberately. → could

This modal hedges between two explanations without committing to either.

16. He ___ not have realised the microphone was still live. → might

The negative of a weak deduction inserts not between the modal and have.

17. The train ___ to have arrived twenty minutes ago according to the board. → ought

Ought keeps its to before have when expressing a disappointed expectation.

18. She ___ have known about the merger; she signed the confidentiality agreement. → must

Documentary evidence supports the strongest positive conclusion about the past.

19. You ___ have left it in the car — you did not take the car today. → can't

A fact that rules the explanation out supports a confident negative deduction.

20. The results ___ be published by now, but the website has not been updated. → should

This modal expresses what is expected rather than what is certain.

Sentence structure: word ordering — answers

1. Draw a confident conclusion about the past. → She must have missed the last train.

Draw a confident conclusion about the past.

2. Deny a past possibility with near-certainty. → He can't have known about the changes.

Deny a past possibility with near-certainty.

3. Suggest a possible explanation without committing to it. → They might have forgotten to book the room.

Suggest a possible explanation without committing to it.

4. Express an expectation about something already due. → The parcel should have arrived on Thursday.

Express an expectation about something already due.

5. Criticise something that was not done. → You should have told me about the delay.

Criticise something that was not done.

6. Criticise something that was in fact done. → They shouldn't have signed without legal advice.

Criticise something that was in fact done.

7. Deduce a present situation from evidence. → The lights are off, so they must be out.

Deduce a present situation from evidence.

8. Deny a present possibility. → That can't be the right platform for Leeds.

Deny a present possibility.

9. Suggest a negative possibility politely. → She may not have seen your message.

Suggest a negative possibility politely.

10. Speculate about a past activity that went on for a while. → He could have been waiting for hours.

Speculate about a past activity that went on for a while.

11. Say that an effort turned out to be unnecessary. → You needn't have come in at all today.

Say that an effort turned out to be unnecessary.

12. Conclude that an unknown person did something. → Somebody must have left the gate open.

Conclude that an unknown person did something.

13. Criticise an omission using the alternative to should. → They ought to have warned the residents first.

Criticise an omission using the alternative to should.

14. Deduce something in progress right now. → It must be raining outside again.

Deduce something in progress right now.

15. Deny a past ongoing action confidently. → He can't have been driving at that speed.

Deny a past ongoing action confidently.

16. Hedge an explanation in a formal report. → The discrepancy could have been a clerical error.

Hedge an explanation in a formal report.

17. Combine a weak deduction with a passive. → She might not have been told either.

Combine a weak deduction with a passive.

18. Deny that anyone had the ability to predict something. → Nobody could have foreseen the collapse.

Deny that anyone had the ability to predict something.

19. Combine a strong deduction with a passive. → The figures must have been checked twice.

Combine a strong deduction with a passive.

20. Use a criticism form as a polite thank-you. → You shouldn't have gone to so much expense.

Use a criticism form as a polite thank-you.