Should have / could have / might have / may have / must have (b)

We use should have / could have + past participle

• to talk about unreal past situations that are the opposite of what actually happened:

She could have moved to Lisbon last year (= but she didn’t).
I could have danced all night (but I did not do so)!
We should have told her she had done an excellent job (but we did not do so).

We can use could have / might have

• to criticise people for not doing things:

He might have volunteered to change the tyre! (Why didn’t he?)
They could have offered us a hand*. (Why didn’t they?)

*offer s.o. a hand – to offer to help someone

We use this structure to talk about things

• that are not certain to have happened, or
• that we suppose (but don’t know for certain) have happened. May have / must have are also common in these senses:

He may have lost his temper* (= I wonder if he lost his temper).
He could have arrived by now (= it is possible he has arrived).
You must have had such a surprise when he walked in the door! (It’s probable you were very surprised….)
She can’t have got the job (= maybe she hasn’t ……)

*Lose your temper – fail to keep control of your anger