The empty seat: should have, could have, would have

“Couldn't you have given the ticket to a friend?” — talking about the past that didn't happen.

In the joke, the first man can't believe it: “Couldn't you have given the ticket to a friend?” To talk about the past that didn't happen, English uses a modal + have + past participle.

Should have

should have + past participle

A criticism or a regret: it was the right thing to do (or what was planned)… but it didn't happen. = aurait dû

I should have been accompanied by my wife, but she died. (Stanley Cup)
He should have gone to the funeral!
He shouldn't have asked that question!

Could have

could have + past participle

A possibility that wasn't used: it was possible… but nobody did it. In a question, it's a suggestion or a reproach. = aurait pu

Couldn't you have given the ticket to a friend or relation? (Richard)
Couldn't you have sold the ticket? (American version)
Somebody could have used that seat.

Would have

would have + past participle

An imaginary result: what would have happened in a different situation. = aurait (fait)

Someone would probably have been delighted to see the match. (American version)
You would have appreciated some company. (American version)
Many of them would have liked to come… (American version)

The form never changes

modal + have (never has, never had) + past participle — for all the persons: I / you / he / they should have gone. Negative: shouldn't have, couldn't have, wouldn't have.

give → givengo → gonecome → comesell → soldbe → beenbuy → boughttell → toldsee → seenlike → likedask → asked

Now practise →

All the activities of the empty seat