must have, might have, can't have
Guessing about the past with confidence, possibility or disbelief.
The rules
- "Must have" = a confident conclusion from evidence: lights off → they left.
- "Might have" (or "may have") = a possible explanation, not certain.
- "Can't have" = confident it's impossible, the evidence rules it out.
- Positive evidence → confident deduction: "must have studied".
- Modal perfect: must + have + past participle.
- "Should have" + past participle = regret/criticism about the past, a different meaning from deduction.
- Dead plant despite being away → nobody watered it: "can't have watered it".
Examples
- The lights are off, they must have gone out.
- I'm not sure, but she might have forgotten the meeting.
- He can't have been at the meeting on Tuesday.
- You must have studied hard, this is an excellent essay.
- She must have left her keys.
- I should have called her sooner.
- The plant is dead, someone can't have watered it while I was away.
Quick check
Pick an answer to see the rule behind it.
1.The lights are off, they _____ gone out.
2.I'm not sure, but she _____ forgotten the meeting.
3.He was in Paris all week. Which sentence is correct?
4.You _____ studied hard, this is an excellent essay.
5.Which sentence expresses regret about a past action (not deduction)?