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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.
Read the explanation to learn more.
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.
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.
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.
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.
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