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.

Contents

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

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.

Can’t/Couldn’t + Have + Past Participle

Express negative deduction (impossibility in the past)

She can’t have passed such a difficult exam.

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)

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.)

Might + Have + Past Participle

Express a past possibility

Our neighbours might have heard some noises when our car was stolen.

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.

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.)

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.)

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.)

Perfect Infinitives with Modal Verbs | Image

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