Perfect infinitive with modal verbs in English: must have, can’t have, should have, shouldn’t have, needn’t have, ought to have, may have, might have, could have, would have.
Must Have + Past Participle
Express a deduction about something that has happened. We feel quite sure about it.
I didn’t hear her voice . She must have gone out.
I cannot find my watch; I must have lost it.
Can’t Have + Past Participle
Describe a deduction about something that didn’t happen in the past based on present evidence.
He can’t have fallen in love with her. She’s married.
This can’t have been an economically sensible decision.
Should Have + Past Participle
Express the idea that something was desirable or needed but didn’t take place.
She should have asked you before borrowing your pen.
We should have had a proper discussion before voting.
Shouldn’t Have + Past Participle
Something took place but it wasn’t desirable.
She shouldn’t have taken the matter too seriously.
Needn’t Have + Past Participle
Express that something was done but it wasn’t necessary. The person who did it thought it was necessary.
He needn’t have been so careful.
I needn’t have knocked at the door since, in this way, I awoke the baby. (but I knocked)
Ought to Have + Past Participle
Express an unfulfilled duty or obligation.
I ought to have come earlier. I deeply regret.
May Have + Past Participle
Express the possibility that an action took place in the past.
Alert readers may have noticed the misprint in last week’s column.
Might Have + Past Participle
Express a past possibility.
Our neighbors might have heard some noises when our car was stolen.
Could Have + Past Participle
Express past reference about something that was not carried out.
You could have done it. (You didn’t do it)
You could have told me I had a snotty nose!
Would Have + Past Participle
Used in the Third Conditional.
I would have gone to university if my parents had had more money. (The speaker didn’t go to university.)
Perfect Infinitive with Modal Verbs | Picture