02 Past deduction
Degrees of certainty in the past
1must have + past participle
Meaning
- we are near certain it happened
Example
- The streets are flooded.
- There must have been a heavy storm last night.
2may have + past participle
Meaning
- we are uncertain it happened
Example
- She may have forgotten about the meeting.
3might have + past participle
Meaning
- we are very uncertain it happened
Example
- They might have heard the announcement.
4can't have + past participle
Meaning
- we are certain it did NOT happen
Example
- They can't have heard the announcement — they didn't show up.
Form
- modal + have + past participle (V3): must have experienced, can't have caused, might have felt.
- Never use the past simple after a modal: must have went is wrong.
Quick check
- The streets are flooded. There … been a heavy storm last night. → must have
- They … heard the announcement — they didn't show up. → can't have
- She … forgotten about the meeting. It's likely. → may / might have