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
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