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Updated: Aug 16, 2022

- it is possible to use modal verbs to refer to the past

- so-called perfect infinitive is used

- THE FORM IS: modal verb + have + past participle


1 part of the third conditional sentence, past unreal actions

Maria would have booked a plane to Greece if she had got money.

If he had bumped into her, he would have asked her out.

2 talking about something we wanted to do but did not

I would have called you, but my phone died.


- to speculate about the past

- to talk about possibilities that something happened or was true in the past


- to make assumptions or guesses about the past (small probability)

I might have won the prize.

- possibility about the real past

Martin could have forgotten to book his ticket. (was able to forget)


1 to make an assumption or guess about the past (I think/I suspect)

could have / might have can be interchangeable

Martina could have lost her wallet in the cinema.

Your grandpa is late. He might have got stuck in traffic.

2 past possibility - talking about something that could have happened but did not

I could have broken the key.

We could have gone to the pub, but we were lazy.

Martin could have forgotten to book his ticket.

3 couldn’t have –(near) certainty about the past, used to talk about something impossible that couldn’t have happened

Me and Mike couldn’t have met 5 years ago. I was living in India, and he was in the US.

They couldn’t have sold the car, I saw them in it just yesterday.

4 annoyance at past behaviour (also might have)

You could have told me you were not coming.


- to express that we are almost sure something didn’t happen or that it is impossible

- we use only couldn’t have for the speculation in the distant past

They couldn’t have been to together that long. They both died in their twenties.

He can’t have left yet. His keys are still here.

We can’t have missed the turn. There weren’t any.

This soup tastes strange. You can’t have followed the recipe.


- to express certainty that something certainly happened

- it is the past form of must but to for making deductions from evidence

- the opposite is can’t have

I must have been crazy to fall in love with you.

She must have gone mad. Look at all those broken things.


- to express a good idea, a regret, criticism, common apologies and when giving advice

I shouldn’t have texted him because he is obviously not interested.

We oughtn’t have proposed that idea. We’re going to pay for it.

I apologize. I should have contacted you earlier.

You should have booked the flight asap.

You shouldn’t have called him.

- Probability about the past

Jane should have finished his lesson by now, shouldn’t he?

- a reaction to gifts

A visitor comes to your house and they bring you a bottle of wine and a box of chocolates. You can reply: 'Oh. Thank you. But. You shouldn't have'. Meaning it was not necessary to bring any gifts.


- somebody did sth but it was not necessary

You needn’t have woken me up. I don’t have to go to work today.