Must have, might have, can’t have
Make deductions about the past: must have left, might have forgotten, can’t have seen — and speculate about what happened.
In this lesson you will
- Use modal + have + participle for past deductions
- Use continuous forms: must have been working
- Speculate about past events with evidence
Learn
must have + participle = sure it happened: The ground is wet — it must have rained.
can’t have / couldn’t have = sure it didn’t happen: She can’t have seen* us, or she would have waved.*
might / may / could have = it possibly happened: He might have missed* the bus.*
Continuous: must have been + -ing: You look exhausted — you must have been working* all night.*
Examples
- The door was locked. Someone must have taken the key.
- They can’t have finished already — they only started an hour ago.
- She might have forgotten about the meeting.
- He must have been waiting for ages.
Vocabulary
speculate
guess without full information
clue
a piece of evidence
explanation
a reason for something
mystery
something not understood
witness
a person who saw something
Practice
Complete the sentence.
Listening: The missing cake
Audio isn’t available in this browser — read the transcript instead.
Ana: Someone’s eaten half the birthday cake!
Leo: It can’t have been me — I’ve been at the gym all afternoon.
Ana: Well, it must have been someone who knew where it was.
Leo: The dog might have got it?
Ana: The dog can’t have opened the fridge.
Leo: True… Oh — there are chocolate fingerprints on Tom’s homework. It must have been Tom!
1.Why can’t it have been Leo?
2.Why can’t it have been the dog?
3.Who do they think ate the cake?
Speaking
Choose a real mystery (a famous one or from your life) and speculate about what happened using past modals of deduction.
Writing
Write a detective’s report (120–150 words) on a small mystery, explaining what must, might and can’t have happened.
Lesson quiz
She ___ have arrived — her coat is here.
Review
Key points
- must have done = sure it happened.
- can’t/couldn’t have done = sure it didn’t.
- might/may/could have done = possibly.
- must have been doing for ongoing past actions.
What you learned
- ✓ I can make past deductions.
- ✓ I can speculate with evidence.
- ✓ I use continuous forms correctly.
Grammar reference: Modals of deduction: must, might, can’t