Modal Perfect Verbs

Must have + verb ( past perticiple ) = conclusion about the past.

Ex: They're late and it's rush hour. They must have gotten stuck in traffic.

Can't have + verb ( past participle ) = conclusion about the past in the negative.

Ex: - " I saw George downtown "

     - " It can't have been George. He's out of town ".

Should ( not ) + have + verb ( past participle ) = judgement about the past.

Ex: I feel terrible today  I shouldn't have eaten so much at the party last night.

Could + have + verb ( past participle ) = possibility in the past. ( It probably didn't happen )

Ex: Why didn't you ask ?  I could have given you a ride.

May (not) + have + verb ( past participle ) = possibility about the past you're not sure about .

Ex: Allan missed the class.  He may have felt sick.  I don't know.  I haven't talked to him yet.

Might (not) + have + verb ( past participle ) = remote possibility in the past. You're not sure about it.

Ex: I don't know where I left my car keys.  I might have left them at the shops. I can't remember.