Must have, might have, can't have

What's in the lesson

1. 1Warm-up
2. 2Reading: meanwhile, back at the campReading comprehension
3. 3How sure are they?Grammar exercise
4. 4Find the guessesGrammar exercise
5. 5How sure are you?Grammar rule
6. 6Sure or not sure?Grammar exercise
7. 7Now or in the past?Grammar exercise
8. 8Who ate the cake?Grammar exercise
9. 9Make the guessesGrammar exercise
10. 10Say it naturallySpeaking practice
11. 11The hotel roomSpeaking practice
12. 12About youGrammar exercise
13. 13Wrap-up

Homework

1. 1Homework: the empty officeGrammar exercise
2. 2Homework: choose the right guessGrammar exercise
3. 3Homework: a detective's notesDiscussion

Two slides from the lesson

Warm-up

A few questions about you before we start.

1. Have you ever lost something and later found it in a strange place?
2. When a friend is late and doesn't call, what do you usually think?
3. Do you like detective stories or mystery shows? Why, or why not?

Grammar rule

How sure are you?

modal + have + past participle

How sure?	Form	Example
almost certain it happened	must have	The grass is wet. It must have rained.
possible	might have / may have / could have	She might have forgotten her phone.
possibly not	might not have / may not have	They may not have seen the sign.
fairly sure it didn't (American English)	must not have	He must not have heard the doorbell.
sure it didn't	can't have / couldn't have	You can't have finished already!

More forms

An activity: The lights were on all night. They must have been studying. · A passive: The window could have been broken by the wind. · A question: Could he have dropped his phone in the taxi? (Could is the usual choice in questions; not May he have…?)

Now or then?

He must be lost (now). · He must have gotten lost (earlier). The past form is have + past participle, not the past simple: must have went → must have gone.

could have also means a danger that didn't happen: He could have frozen to death in the forest, but he survived.