Using Perfect Infinitives with Modal Verbs

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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Using Perfect Infinitives with Modal Verbs

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