Past actions
When expressing past actions, might, may, could, must and should precede
have + past participle, as in the following example.
The explosion was very loud. Even people living several kilometers away
must have heard it.
To form a negative past tense modal sentence, use modal + not + have +
past participle.
Tom is usually a good student , but he did
poorly on the last test. He might not
have understood the instructions.
To say you think an action was happening at a time in the past, use
modal + have been + progressive verb, as in the next example.
The fire alarm sounded very early in the
morning. Most residents of the building
must have been sleeping at the time.
1. Might have, may have, could have
Might have, may have and could have are used to show past
possibility. In other words, they are
guesses about what happened at a period before now. See the examples below.
I can’t find my glasses. I might have left them in the car.
She promised to be here by now, but I don’t
see her. She may have missed the bus.
The lights are all off in the house next
door.. Our neighbours could have gone
out.
2. Could have
Could have is also used to talk about something the speaker was able to
do in the past but didn’t.
We were all having so much fun that we could
have stayed longer. (We didn’t stay
longer.)
I could have finished the report if I had
stayed longer at the office. (I didn’t
stay longer at the office. I went home.)
3. Must have
Must have is used to show probability in the past. That is, the speaker is almost certain that
an action took place at a time before now.
There’s no milk in the refrigerator. We must have drunk it all.
Many more cars than usual were parked on our
street last night. Someone must have had
a party.
4. Should have, ought to have for advice
Should have and ought to have are used to express advice or offer an
opinion regarding the past. It refers to
an action that would have been ood or appropriate, but never happened.
John missed the bus. He should have left his house a few minutes
earlier. (He didn’t.)
John missed the bus. He ought to have left his house a few minutes
earlier.
5. Should have, ought to have for expectation
Should have and ought to have are also used to express past expectation.
John should have been here by now. (I expected him to be here by now, but he
isn’t.)
John ought to have been here by now.
6. Using “not”
The use of not with a past tense modal expresses the idea that whatever
action took place was not good or appropriate. Consider the following examples.
I should not have drunk so much coffee. Now, I can’t sleep.
My suitcase is too heavy. I shouldn’t have packed so many things.
