He might have forgotten that we were meeting today.ġ: Should have + past participle can mean something that would have been a good idea, but that you didn't do it.

We can also choose to use might have + past participle to mean the same thing: He could have forgotten that we were meeting today.We're just talking about our opinion of what maybe happened. (See also modals of probability.) In this case, we don't know if what we're saying is true or not true. It's a really, really difficult exam.Ģ: We use could have + past participle when we want to make a guess about something that happened in the past. He couldn't have passed the exam, even if he had studied harder.There was a terrible traffic jam (= it was impossible for me to have arrived any earlier). He could have studied harder, but he was too lazy and that's why he failed the exam.Ĭouldn't have + past participle means that something wasn't possible in the past, even if you had wanted to do it.Julie could have bought the book, but she borrowed it from the library instead.They could have won the race, but they didn't try hard enough.I could have stayed up late, but I decided to go to bed early.Could have + past participleġ: Could have + past participle means that something was possible in the past, or you had the ability to do something in the past, but that you didn't do it. These past modal verbs are all used hypothetically, to talk about things that didn't really happen in the past.

Perfect modal verbs exercises