It may/could/must have been, etc

A Introduction

Vicky, Emma and Matthew are at a club in town.

Vicky: Where's Daniel? He should have been here half an hour ago.

Emma: He may have got lost. It isn't easy to find this place.

Matthew: He could have forgotten all about it, I suppose.

Emma: He can't have forgotten. We were talking about it this morning.

Matthew: Well, something must have delayed him.

We can use a modal verb with the perfect (have + a past participle). We use this structure to talk about possible past events.

We use these forms to say that possibly something happened in the past.

He may have got lost. (Perhaps he has got lost.)

You might have left your keys at work. (Perhaps you left them at work.)

Someone could have stolen them. (It is possible that someone stole them.)

We also use could have for an opportunity that we didn't take or a possible result that didn't happen.

We could have gone out somewhere, but we were too tired.

You were very lucky. There could have been a terrible accident.

Compare these different uses.

MAY/MIGHT NOT HAVE Possibly something did not happen.

Daniel may not have caught the bus. I expect he missed it. (Perhaps he didn't catch it.)

I might not have locked the door. (Perhaps I didn't lock it.)

COULDN'T HAVE It is impossible that something happened.

Daniel couldn't have caught the bus. It doesn't run on Sundays. (It is impossible for him to have caught the bus.)

Must have and can't have are opposites.

MUST HAVE

My watch says it's only ten past two. It must have stopped. (I realize it is certainly true that my watch has stopped.)

CAN'T HAVE

You've only spent five minutes on that job. You can't have done it properly. (I realize it is impossible that you did the job properly.)

We use these forms when someone didn't do the right thing.

We didn't play very well We should have played better.

I got lost. ~ Sorry. I ought to have drawn you a map.

It was a lovely old building. They shouldn't have knocked it down.