
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. 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.
Peter
The LearnEnglish Team
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.
Peter
The LearnEnglish Team
Hello BobMux,
Perfect forms relate a later state or event to an earlier state or event, and the perfect modal forms are no different.
These forms are used for deductive reasoning, relating present evidence or knowledge to a past situation or action:
Peter
The LearnEnglish Team
Hi majesticdagny,
Yes! The passive is fine to describe this action/event.
Jonathan
The LearnEnglish Team
Hello wasan0909,
Aside from punctuation, the first two sentences are correct, though we would only write contractions like might've in a very informal context; generally we only contract have when used with pronouns (I, you, we etc).
The third sentence is not correct. We don't use can have for speculation. You could use might have, may have or could have instead.
Peter
The LearnEnglish Team
Hello Leila77,
In the context of deduction about the past as described on this page, there is no difference.
For more information about can and could, including can have and could have, you can visit this page:
https://learnenglish.britishcouncil.org/english-grammar-reference/can-and-could
Peter
The LearnEnglish Team
Hi kyawkyawsoezhu,
Yes, it is part of a third conditional structure! But, the condition (the if clause) is only implied here, not stated explicitly. In full, it would be: I'm sure he would have told me if he'd known. But the first sentence implies the if he'd known part, so the speaker omitted it.
Does that make sense?
Best wishes,
Jonathan
The LearnEnglish Team
Hello Jamalmoghni,
There are many different forms which use have and have been, both as main verbs and as parts of other verbs (perfect forms, passive forms etc). Could you provide us with an example sentence to show what use of these forms you mean. Then we'll be sure we're giving you the right information.
Peter
The LearnEnglish Team
Hello Raaz Gupta,
The modal verb 'could have' has many different uses. One of these is to express deductions about the past, and this is what is described on this page.
You can see other uses of 'could' (including 'could have') -- for example, to express possibility, as in your first example sentence -- explained on our 'can' and 'could' grammar page. I'd also recommend having a look at the Modals with 'have' page as well.
Please note that we don't generally comment on other grammars, but if you see something in the one you are familiar with that seems to differ from what you read here, you are welcome to ask us a specific question about it.
All the best,
Kirk
The LearnEnglish Team
Hello Eman_Alhindal,
This is a sentence with a superlative form ('the most uninspiring') and a reduced relative clause. If we add the relative pronoun back to the sentence, it is: '... documentary that I have ever watched'.
Does that help? Feel free to ask us a specific question if it's still unclear.
All the best,
Kirk
The LearnEnglish Team
Hello Eman_Alhindal,
If I say 'You can't be hungry' to you, it means that I think it's not possible that you are hungry. Perhaps I've just seen you eat a lot of food, for example, and so now it's hard for me to believe that you are still hungry.
'You're not hungry' is less specific and so it could be used in many situations. For example, maybe I believe you're not hungry because I just saw you eat, or maybe I'm encouraging you not to eat when you appear tempted to have a piece of cake. The meaning here is much more dependent on the context than the first one.
As for the last two sentences, in many cases they would mean the same thing. The first one could suggest you've already made arrangements to go -- i.e. that you already have a ticket for the event -- than the second one, which could indicate an intention to go more than having taken action to go (i.e. you might not have a ticket). But in ordinary speaking, most of us are not so precise, and so you could often say one or the other and mean the exact same thing.
All the best,
Kirk
The LearnEnglish Team
Hello Inci Ozturk,
Can't have is used to express something that the speaker thinks was not possible. Thus, the speaker is saying this:
The speaker remembers paying for the taxi and the implication is that this is proof that the speaker had the wallet at that time. Therefore it is not possible that it was left it in the restaurant.
Must have would have the opposite meaning.
Peter
The LearnEnglish Team
Hello ryankht,
Perfect modals like mustn't have do have a past meaning, but they are not past forms of the modal verbs. For example:
With modal verbs, the context is crucial. I think for your second question you really need to provide concrete examples of what you have in mind so that we can be sure we understand properly.
Peter
The LearnEnglish Team
Hello Vinod,
Yes, it's possible to use may have in this way but only for something which is not part of a constant routine. It implies that you are speculating, and it's most often used with a verb which also indicates this:
When we are talking about a situation which is constant - something normal such as an everyday routine rather than something Mr. David might do on a particular occasion - then just have to is used:
You could replace may with might in the first instance without changing the meaning.
It is possible to say must have to. The meaning is something like must be obliged to and it is used when you are speculating about what is required of another person.
Peter
The LearnEnglish Team
Hi vinod,
Thank you for saying so! We try to response as quickly as we can, though sometimes it takes some time. If you post a question in the comments section of any page it will be read by someone on our team and we will try to respond. It may be me or it may be one of my colleagues - there's no need to address the question to anyone in particular.
Peter
The LearnEnglish Team
Hello carmenwf.jung,
Yes, that's correct. When we are making deductions about the past we use perfect modal verbs:
Peter
The LearnEnglish Team
Hello Rsb,
I've answered this question on another page for you. We reply to questions as quickly as we can, though we are a small team here. If you post the same question multiple times then it only slows the process down.
Peter
The LearnEnglish Team
Hello Bharati,
This is very similar to your question/statement on the conditionals page, so I'll refer you to my answer there:
https://learnenglish.britishcouncil.org/grammar/intermediate-to-upper-intermediate/conditionals-1
Peter
The LearnEnglish Team