Could have, should have, would have

Could have, should have, would have
Could have + past participle
1: 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.
• I could have stayed up late, but I decided to go to bed early.
• They could have won the race, but they didn t try hard enough.
• Julie could have bought the book, but she borrowed it from the library instead.
• He could have studied harder, but he was too lazy and that s why he failed the exam.
Couldn t have + past participle means that something wasn t possible in the past, even if you had wanted to do it.
• I couldn t have arrived any earlier. There was a terrible traffic jam (= it was impossible for me to have arrived any earlier).
• He couldn t have passed the exam, even if he had studied harder. It s a really, really difficult exam.
2: We use could have + past participle when we want to make a guess about something that happened in the past.
In this case, we don t know if what we re saying is true or not true. We re just talking about our opinion of what maybe happened.

Why is John late?
• He could have got stuck in traffic.
• He could have forgotten that we were meeting today.
• He could have overslept.
We can also choose to use might have + past participle to mean the same thing:
• He might have got stuck in traffic.
• He might have forgotten that we were meeting today.
• He might have overslept.