The structure “have + past participle” is called a perfect infinitive.
In this lesson, we will learn about the combination between modal verb and perfect infinitive.
Form:
MODAL + HAVE + PAST PARTICIPLE
Usage:
- to refer to the past
- to refer to unreal situations
- to show that the activity was different from what we wanted
- to say how confident we are that something has happened
1. Must + Have + Past Participle
Express deduction, a logical conclusion, probability
- It is very cold; it must have snowed in the mountains.
- If you can’t find your car keys, you must have left them in the house.
2. Can’t/Couldn’t + Have + Past Participle
Express negative deduction (impossibility in the past)
- She can’t have passed such a difficult exam.
3. Could + Have + Past Participle
Express past reference about something that was not carried out
- You could have done it. (You didn’t do it)
- She could have called the doctor early in the morning. (She didn’t call the doctor)
4. May + Have + Past Participle
Express the possibility that an action took place in the past
- The little girl may have lost the key. (It is possible that she lost the key.)
5. Might + Have + Past Participle
Express a past possibility
- Our neighbours might have heard some noises when our car was stolen.
6. Needn’t + Have + Past Participle
Express an unnecessary action, which was, nevertheless, performed
- I needn’t have knocked at the door since, in this way, I awoke the baby. (But I knocked)
- You needn’t have bought the flowers.
7. Should + Have + Past Participle
Indicate that the past obligation was not fulfilled or carried out
- You should have locked the door before leaving the house. (But you didn’t lock it.)
8. Ought to + Have + Past Participle
Express an unfulfilled duty or obligation
- Paul ought to have waited until the lights were green before he crossed the street. (But he didn’t wait.)
9. Would + Have + Past Participle
The third conditional
- I would have gone to university if my parents had had more money. (The speaker didn’t go to university.)
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