1. PERFECT MODAL VERBS
Must + have + past participle : it expresses deduction in the past.
Mary is very sensitive. She must have passed a bad time when her child got sick.
Can’t + have + past participle : it expresses impossibility (negative deduction) in the
past.
Mary is very sensitive. She can’t have passed a good time when her child got sick.
Should (not) + have + past participle : it expresses regret about something we did
wrong in the past.
You should have apologized your parents but you did not pay attention to me.
You shouldn’t have gone so early last night.
- It can also express probability about something we expected to happen but we are
not sure if it has already happened.
They should have arrived by now, but I don’t know if they have.
Or to express that the expected action has not occurred in fact.
They should have arrived but they are not here yet.
Could + have + past participle : a possible action in the past that was not fulfilled.
I could have passed my exam but I didn’t study enough.
NOTE: compare it with this:
I couldn’t study so I didn’t pass my exam. ( It was impossible for me to study )
May/might + have + past participle : it expresses possibility in the past.
I have been phoning John all afternoon and he was not there. He may have left
home earlier. (Maybe, he left before)
- We can also express possibility about something that didn’t really happened in the
past (Only with might).
Why did you drive so fast? You might have crashed.
Needn’t + have + past participle : it says that we did something although it was not
necessary to be done.
You needn’t have come. Why have you done it?
NOTE: compare it with this:
You didn’t need to come, so you didn’t do it.