Must have, can’t have

  • B2 · Upper-intermediate
  • Grammar lesson
  • 60 min

Guessing about the past from the evidence: must have, might have, could have and can't have + past participle (The crew must have left in the lifeboat. Pirates can't have attacked: the cargo was still there.). The student reads about the Mary Celeste, the ship found with no one on board in 1872, turns clues into conclusions, and argues a theory at the inquiry.

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must havecan't havemight have

What's in the lesson

  1. 1Warm-up
  2. 2In this lesson
  3. 3Reading: the ship with no one on boardReading comprehension
  4. 4What does it mean?Grammar exercise
  5. 5Find the guessesGrammar exercise
  6. 6must have, might have, can't haveGrammar rule
  7. 7Clues and conclusionsGrammar exercise
  8. 8How sure?Grammar exercise
  9. 9Say it with a modalGrammar exercise
  10. 10Find the mistakeGrammar exercise
  11. 11Say it naturallySpeaking practice
  12. 12The inquirySpeaking practice
  13. 13About youGrammar exercise
  14. 14Wrap-up

Homework

  1. 1Homework: Grandma's trunkGrammar exercise
  2. 2Homework: which guess is right?Grammar exercise
  3. 3Homework: build the guessesGrammar exercise
  4. 4Homework: an old photoDiscussion

Two slides from the lesson

Warm-up

A few questions about you before we start.

  1. Do you know any famous unsolved mysteries? Which one interests you most?
  2. Have you ever come home and found something there that you couldn't explain? What did you think had happened?
  3. When something goes missing in your home, who or what do you usually blame first?

Grammar rule

must have, might have, can't have

modal + have + past participle: guesses about the past

How sure are you?FormExample
almost sure it happenedmust have + past participleThe parking lot is full. Half the town must have shown up for the sale.
it's possiblemight have / could have (more formal: may have)That noise might have been the neighbors' cat.
possibly notmight not have (or may not have)They might not have noticed the mistake.
almost sure it didn't happencan't have / couldn't haveShe can't have walked home: it's twelve miles.
a questionCould + subject + have + past participle?Could the letter have gone to our old address?

How we use it

  • We look at the evidence and draw a conclusion. The evidence often comes next, after because, so or a colon.
  • With be: must have been + adjective, -ing or past participle. The road must have been closed. They must have been sleeping.
  • In American English, must not have means "fairly sure it didn't": The coach must not have checked his email. (mustn't have is rare.)

Watch out

  • can is not for guesses about the past: can have → could have or might have. Only the negative works: can't have.
  • After have, the past participle: must have went → must have gone; might have saw → might have seen.
  • In questions, use could, not may: not May they have…?
  • could have has two uses. A guess: It could have been a fox (maybe it was). A missed chance (unit 1): We could have stayed longer (but we didn't). The context tells you which.
  • Now or then? She must be at work (now). She must have been at work (earlier).
  • In speech, have is weak: must've, might've, could've. Never write must of.

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← Unit 2Needn’t have, didn’t need to