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: 4.1 (80 votes)

Hi Kabir Sharma,

I see what you mean, and I can see why confusion is possible. But for me the intended meaning of the sentence is clarified by the "were done correctly" part, as you pointed out. 

To avoid confusion, we could simply use "could" --> "The tasks that could be done correctly were done correctly." 

Best wishes,


The LearnEnglish Team

Submitted by aymen009 on Sat, 18/06/2022 - 23:11


hi i need help with this senario (“One day your colleague doesn’t arrive at work. This is unusual because he has never been sick in the
past. When you ask your boss about him, she tells you that he contacted the company to say that he was
sick. He returns to work two weeks later. He has lost a lot of weight but looks very healthy and has a good
suntan. You also notice that he is very calm when he works and does not seem to get as frustrated as he
did in the past with you or his other colleagues.) and this question about it Why did your colleague take time off work?
How can you explain his physical condition?
How can you explain his new calm manner?
A few days later you talk to your colleague. Here are some of things he told you:
He was feeling burned out and needed a break from work.
He went on a 10-day meditation vacation.
He now meditates regularly and follows a vegan diet.

Submitted by Robi Pokrajac on Thu, 16/06/2022 - 22:32


Hi there, I would appreciate your help. The sentence: "The examples that did not fit the scheme or may have been described more accurately were processed additionally." Is "may have been" used correctly here? Thank you!

Hello Robi Pokrajac,

I think you probably need 'could have been', 'should have been' or 'needed to be' here, but it's really not possible to be sure without knowing the context and what you are trying to say.



The LearnEnglish Team

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