This document discusses the use of past modal verbs like must, may, might, can't, and couldn't followed by the past participle to speculate or deduce about past actions. It explains that must have is used when you are almost certain something happened, might/may/could have express possible actions, and can't/couldn't have indicate when something was almost surely not possible. Examples are provided to illustrate the use of each modal.

1. Past Modals
NEF Upper-Intermediate 4B

2. Must/may/might/can’t/couldn’t +
have + past participle
• To make deductions or speculate about past
actions

3. I must have passed the exam.
I’m sure I got all the answers right
You must have seen something.
You were there when the robbery happened
must have
• Use must have + past participle when you’re
almost sure that something happened or was true

4. Somebody might have stolen your bag when
you were getting off the train
He still hasn’t arrived. I may have not given him.
The right directions
might/may/could have
• Use might/may/could have + past participle when
you think it’s possible sure that something
happened or was true

5. They can’t have gone to bed yet. It’s too early.
They can’t have seen us. It’s too dark.
can’t have
• Use can’t/couldn’t have + past participle when
you’re almost sure that something didn’t happen
or that it’s impossible