Modals: deductions about the past

Modals: deductions about the past

Do you know how to use modal verbs to show how certain you are about past events? Test what you know with interactive exercises and read the explanation to help you.

Look at these examples to see how must, might, may, could, can't and couldn't are used in the past.

An earthquake? That must have been terrifying!
We don't know for sure that Alex broke the coffee table. It might have been the dog.
How did she fail that exam? She can't have studied very much.

Try this exercise to test your grammar.

Grammar test 1

Modals – deduction (past): Grammar test 1

Read the explanation to learn more.

Grammar explanation

We can use modal verbs for deduction – guessing if something is true using the available information. The modal verb we choose shows how certain we are about the possibility. This page focuses on making deductions about the past.

must have

We use must have + past participle when we feel sure about what happened.

Who told the newspapers about the prime minister's plans? It must have been someone close to him.
The thief must have had a key. The door was locked and nothing was broken.
Oh, good! We've got milk. Mo must have bought some yesterday.

might have / may have

We can use might have or may have + past participle when we think it's possible that something happened. 

I think I might have left the air conditioning on. Please can you check?
Police think the suspect may have left the country using a fake passport.

May have is more formal than might have. Could have is also possible in this context but less common.

can't have / couldn't have 

We use can't have and couldn't have + past participle when we think it's not possible that something happened.

She can't have driven there. Her car keys are still here.
I thought I saw Adnan this morning but it couldn't have been him – he's in Greece this week.

Do this exercise to test your grammar again.

Grammar test 2

Modals – deduction (past): Grammar test 2

Language level

Average: 4 (85 votes)

Thank you very much, Peter.
Well, my intention was to say something like that there were those additional examples that did not fit the original scheme and that there was a possibility of explaining them more accurately. A paraphrase would be "They were possible to be explained more accurately"
So I used may have been to indicate possibility
What do you think?

Hello again.

In that case I think 'could have been' is the best option. May have been would carry a sense that something was possible but unknown. Could have been can have this meaning too, but can also mean that there was the possibility of doing something differently. For example:

She could/may/might have missed the train. [this is a possibility; I don't know if it is true]

She could have worked harder. [the possibility was there but was not taken]

Your sentence seems closer to the second:

The examples that did not fit the scheme or could have been described more accurately were processed additionally.



The LearnEnglish Team

Submitted by Muhammadqodir on Sat, 04/06/2022 - 05:57


Hello what is the difference neednʼt have and shouldnʻt have

Hi Muhammadqodir,

"Needn't have" means that it was not necessary to do something (e.g. "We needn't have taken heavy jackets. It was a hot day."). It may imply it was a waste of time or resources.

"Shouldn't have" means that it was a mistake to do something, i.e. it's a criticism (e.g. "We shouldn't have taken heavy jackets. They were too heavy to carry.")

I hope that helps.


The LearnEnglish Team

Submitted by Anstasia on Sun, 29/05/2022 - 18:26


hello the learnenghlish team. Can I express deduction by modals and to be used to (get used to) at the same time. e.g. Can I use that "My mom may have been used to getting early. She milked cow every morning"
Or is it wrong?
Thank you in advance

Hello Anstasia,

Yes, it's possible to do that. In this case, I might suggest using 'must' instead of 'may' ('My mom must have been used to getting up early'), but it's perfectly fine to say 'My mom may have been used to getting up early'. The one with 'may' expresses more uncertainty and the one with 'must' expresses more certainty -- as if it's what makes most sense.

All the best,
The LearnEnglish Team

Profile picture for user Ahmed Imam

Submitted by Ahmed Imam on Mon, 28/03/2022 - 15:33


Hello. Could you please help me? Which one is correct or both? Is there a difference?
A: Last term, I took four exams and passed them all!
B: You (couldn't - can't) have been disappointed.
Thank you.

Hello Ahmed Imam,

In this context I think both are possible and there is no difference in meaning.



The LearnEnglish Team

Submitted by Natasa Tanasa on Mon, 07/03/2022 - 16:11


Hello everyone,

Could you please tell me if this sentence is correct and how to use CAN after IF clause while using THIRD conditional:

I wouldn't have used the car park if I could park on the street

Thank you!

Hello Natasa Tanasa,

This is an example of an unreal past conditional in which both the condition (the if-clause) and the result (the result clause) are describing imaginary events in the past. The best option is 'had been able to':

I wouldn't have used the car park if I had been able to park on the street.



The LearnEnglish Team