Modal verbs for expressing past probability (deduction)

Must have, can't have, couldn't have:
expressing past probability
Structure: modal verb + have + past participle
must have been, can't have gone, couldn't have gone, etc.
We use must have to express that we feel sure that something was true in the past. They must have left early.
He must have already gone.
We use can't have or couldn't have to say that we believe something was impossible in the past. He can't have escaped through this window – it’s too small.
She can't have said that.
She couldn't have said that.
May / might / could have: expressing past probability
Structure: modal + have + past participle
may have been, could have gone, might have lost, etc.
We use may have, could have, might have to say that it was possible that something happened in the past (but we are not 100% sure). He may have missed the bus.
The road might have been blocked.

(= ‘I think the road was blocked, but I’m not 100% sure.’)
The negatives are may not have and might not have. We don’t use couldn’t have in the same way. He may not have left yet.
I might not have given her the money; I’m not sure.

I could not have given her the money, I’m not sure.

Practise this grammar: modal verbs for past probability exercise – must have, can’t have, could have, might have (intermediate)

See also: ‘must have’ vs. ‘had to’

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Stuart is an English teacher and runs the Speakspeak website. He currently lives in Prague and has been teaching English for 20 years.