Modals of Deduction — Past (must have / might have / can't have)

B2 — grammar, listening, reading, writing

Kenji: Ben's not answering his phone.

Sofía: He must have lost it again.

Kenji: It's only been a week since the last one!

Abuela Carmen: He can't have learned his lesson yet, then.

Common mistake: “He must lost his phone yesterday.” — Correct: “He must have lost his phone yesterday.”

To guess about something in the past, add 'have' between the modal and the past participle — must have, might have, can't have.

• ~95% sure must have + participle — deduced that an action definitely occurred
• ~95% sure not can't have + participle — deduced that an action was impossible
• ~50% possible might / could have + participle — possible that an action took place

• Ben must have dropped his phone in the sea again.
• Someone might have taken the wrong bag by mistake.
• She could have forgotten the meeting.
• They must have left already — the lights are off.
• It can't have been Sofía; she was with me all afternoon.
• He can't have finished already — it's only been five minutes.
• They might not have received the message.
• Could he have missed the bus?
• Do you think she might have forgotten?
• Might they have left without us?
• Did Ben lose it on purpose? He can't have — he loved that phone.
• Could she have called earlier? She might have.
• Did they forget the address? They must have.

Practice

1. Ben ___ lost his phone again. (must have, must, have must)
2. It ___ have been Sofía, she was with me. (can't, mustn't, doesn't)
3. They ___ have left without us — maybe. (might, must be, can)
4. 'He must lost it' is correct.
5. 'Must have + participle' guesses about the past.
6. 'Can't have' is the negative form of 'must have' for deduction.
7. She ___ have forgotten the meeting. (almost sure)
8. It ___ have been him, he was working. (almost sure NOT)
9. They ___ have missed the bus. (possible)
10. Unscramble: he, must, have, dropped, his, phone, again
11. Unscramble: it, can't, have, been, Sofía
12. Find the mistake: He must lost his phone yesterday.
13. I'm almost sure Ben dropped his phone. — Rewrite using 'must have'.
14. I'm almost sure it wasn't Sofía. — Rewrite using 'can't have'.
15. Maybe they missed the bus. — Rewrite using 'might have'.
16. He must have finished. — Write the negative deduction (use 'can't have').
17. Do you think Ben lost his phone on purpose? (short answer, No)

Listening

Sofía: Ben still isn't answering.

Kenji: He must have lost his phone again — it's the third time this year.

Sofía: Or his battery might have died. He never charges it.

Abuela Carmen: It can't have died, he charged it at my house this morning.

Kenji: Then he must have dropped it somewhere. Classic Ben.

Reading

By the time Ben finally called back, everyone had a theory. Sofía was sure he must have left his phone at the beach — again. Kenji thought he might have dropped it on the bus, since Ben always sits by the window with the door open. Abuela Carmen refused to guess: 'He can't have lost it the same way twice,' she said, 'even Ben isn't that unlucky.' When Ben finally explained, the truth was worse than any of their guesses: he had lent it to a stranger to make a call and never got it back. 'You must have known better than that,' Abuela Carmen sighed.

• Sofía thought Ben must have left his phone at the beach.
• Kenji was sure Ben sold his phone.
• Ben actually lent his phone to a stranger.
• Abuela Carmen believed he lost it the same way as before.