Modals: deductions about the past
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
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
Hello again Shetu Yogme,
We distinguish between tense (a form of the verb showing when an action occurred) and aspect (showing other elements of meaning such as completion, repetition etc). English strictly has two tenses: past and nonpast/present. Everything else is aspect or mood. For definitions and examples you can take a look at the relevant wikipedia page:
https://en.wikipedia.org/wiki/Uses_of_English_verb_forms#Tenses
Peter
The LearnEnglish Team
Hello dear teachers 🖐
In what situation, we can use may have+past participle,might have+past participle and could have+past participle interchangeably?
Thanks.
Hello jassa,
When we are making logical deductions about past events based on present evidence and want to say 'there is a possibility that this happened' we can use these interchangeably:
Peter
The LearnEnglish Team
Thanks dear sir.One more question🙋
What is the difference between 'Would have+past participle', 'should have+participle','could have+participle' and 'may/might have+participle'?
Hello jassa,
Modal verbs have multiple meanings depending on the context. Most commonly, would have is used to express a belief about a hypothetical past situation, should have expresses advice or expectation and may/might have expresses possibility. You can read more on this topic here:
https://learnenglish.britishcouncil.org/grammar/english-grammar-reference/modal-verbs
Peter
The LearnEnglish Team
Thanks dear teacher. One more questions-
One thing is common that all those modal verbs(with have+past participle) are used to talk about the past(it can be possibility,probability,regret,criticism etc. in the past)?
Is it true?
Hello jassa,
Yes, that's right.
Peter
The LearnEnglish Team
Hello and thank you in advance.
I've read this sentence in a book:
“You got a letter while you were away. Sorry—I opened it. I thought it must be for me.”
I was taught that the past of “must” is “must have been” for past speculation.
Why isn’t the sentence: “Sorry—I opened it. I thought it must have been for me”?
Hello Teresa R.,
We use must have + verb 3 to talk about something that (we believe) was true in the past but is not true anymore. For example:
The sky is blue but there are puddles on the road. It must have rained last night. [it is not raining any more]
Contrast with must + verb, which describes something still true:
Look at the trees shaking. It must be very windy. [it is windy now]
The time here refers to the action being described, not our belief.
In your example the state of the letter does not change. It does not start being for you and later change. All that changes is your belief, so there is no need to use a perfect modal.
You can compare it to a non-modal form. You would not use a perfect verb here because the fact about who the letter was to did not change, so you would say I thought it was mine and not I thought it had been mine.
Peter
The LearnEnglish Team
Hello LearnEnglish Team,
We can use could have instead of may/might have when we think it's possible that something happened. But the sentence with could have + past participle can seem a conditional one:
I think might have + past participle, too, can refer to the same meaning:
It will be great help if you would explain.
Shetu Yogme.