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 andyroo,
Yes, you are absolutely right. I'm not sure what I was thinking! I've amended my previous comment so that no one gets confused.
Thanks for taking the time to point this out to us!
All the best,
Kirk
LearnEnglish team
Hi, everyone! I am in desperate need for help!
I keep finding different information when it comes to negative past modals of deduction:
Some materials will say that it is possible to say:
"I must not have seen her" as well as
"I couldn't have seen her"
Others say that the only possibility is "couldn't have" and that "mustn't have" is never used as a modal of deduction. I'm completely lost!!!!!
Hello DANIELEBRAUER,
I (native English speaker from the north of England) would not use mustn't have in this kind of context but that's not to say that it does not occur in some dialects of English.
I do sometimes use 'must have' with a negated past participle. For example:
Note there is a difference in meaning here between couldn't have seen and must have not seen:
> couldn't have seen - this action is not logically possible
> must have not seen - this is the only possible explanation
Obviously, in the context of justifying myself the second is more useful!
Peter
The LearnEnglish Team
Hello!
Could you please say if it is correct "You must have me confused with other person" or am I to say "You must have confused me with other person"?
I'm grateful for your helpful work and thank you very much for answering this post beforehand!
Hi howtosay_,
No worries. Thanks for posting your questions :)
Both of these are grammatically correct. The first sentence (have + object + confused with something) refers to now - the person is confused right now.
The second sentence (have confused + object + with something) is the present perfect and it refers to a confusion that has already happened.
It should also be "another person" (instead of "other person"). Hope it helps!
Jonathan
The LearnEnglish Team
Hello, I'm wondering if what I wrote is correct:
"The referee could have disallowed the goal and the same controversy would have remained."
Context: there was a controversial goal. Some people said it was a goal, while others said it shouldn't have stood. I think that in case the referee had disallowed the goal the controversy would have remained.
My problem: I feel my phrase is not completely right because it combines two past-modal verbs "could have" + "would have". Maybe this is not a right structure.
Thanks in advance.
Hello wilson3827,
The sentence is fine. The first part describes an imagined past and the second describes an imagined result. In conditional constructions we generally do not use a modal verbs in the if-clause (If the referee had... then... would have...), but this is not a conditional construction - perhaps this is the source of your uncertainty.
Peter
The LearnEnglish Team
Few people went to the lecture about animal sounds: she could/must have been very disappointed.
Hello! I'd like to ask you if both options are acceptable here. It's a single sentence taken from an exercise, no further context is given.
Must have been refers to the idea of "certainty", while "could have been" conveys the concept that "she was probably disappointed, but maybe not".
What would you suggest? Thanks a lot beforehand!
Hi Marco Gaiotto,
"Could have been" is certainly grammatically possible and meaningful here, and if this was said in a real life conversation it would be acceptable. But "must" seems the most obvious answer and that would be my first choice, in a grammatical practice exercise.
I hope that helps.
Jonathan
The LearnEnglish Team
Hello, I need some help on this question. Is adding has + present perfect to a modal verb the same as a perfect infinitive? So is "you should have done the same" as "you are supposed to have done"?