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  3. Modals: deductions about the past

Modals: deductions about the past

Modals: deductions about the past

Do you know how to use modal verbs to show how certain you are about past events? Test what you know with interactive exercises and read the explanation to help you.

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

Modals – deduction (past): 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

Modals – deduction (past): Grammar test 2

Try another grammar lesson
Average: 3.8 (162 votes)

Submitted by Seti21 on Mon, 09/02/2026 - 10:24

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Hi, I have a question about this sentence, Why could'nt have is correct: 

I was amazed by her performance. She couldn't / can't / 
mustn't have spoken more convincingly in the debate. 

Hello Seti21,

It's possible to use either couldn't have or can't have to speculate about the past. However, in this sentence the speaker ('I') is not speculating, but rather making a comment about ability. We know this because the speaker was present at the performance and is therefore giving an opinion about 'her' capability. Therefore, the modal verb describes ability, not logical deduction. To describe ability in the past we couldn't have is the only possibility here.

 

Peter

The LearnEnglish Team

In my opinion, i think the other 2 (can't and mustn't) are referring more to that the person who speaks is very sure about that she can't perform better, but in fact who knows, so she could perform better anyway.

Submitted by Winnie0900 on Mon, 01/12/2025 - 16:39

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  1. There's a burnt smell coming from the kitchen. I must have left something on the stove!
  2. My friend didn't go to school yesterday. She might have been ill.
  3. She can't have bought that phone by herself. She doesn't have a job. 
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Submitted by MounirBr44 on Wed, 27/08/2025 - 15:42

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𝕌𝕤𝕖𝕕 𝕔𝕒𝕣 𝕠𝕟𝕝𝕚𝕟𝕖 𝕞𝕒𝕣𝕜𝕖𝕥𝕡𝕝𝕒𝕔𝕖 𝕨𝕚𝕥𝕙 ℂ𝕝𝕚𝕔𝕜 & ℂ𝕠𝕝𝕝𝕖𝕔𝕥 𝕤𝕖𝕣𝕧𝕚𝕔𝕖 𝕚𝕟 𝕥𝕙𝕖 𝕌𝕂:

Customer: I wanted to buy this car, and it might have been good for hot weather and long distances.

Seller: Also, if you bought this car, you probably wouldn’t be able to find spare parts for it in your country.

Customer: You’re right, thank you.I think I may have found the right service on your website before contacting you.

Seller: We appreciate your trust. You must have been taking your car to Africa! 

Customer: Of course. My previous imported car used to break down a lot. It just couldn’t have managed the harsh weather conditions there.

Seller: I see. Don’t worry. I’ll help you find a suitable car, with installment payment options and free delivery. It will be of good quality and reasonably priced.

Submitted by MinhLuu on Sat, 02/08/2025 - 06:51

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Hi, I have a question regarding the meaning of modals in specific context. From online research and my experience of teaching, it seems their perfect forms and negative can impact their functions, like in the case of possibility where must have is used to express affirmation while can't have is used for the negative form. I tried searching on some of the English language corpus and notice that the negative form of must have is also possible, albeit at a less common frequency. So, my questions are:

  1. Is it a very rigid rule that the negative form of the same perfect mood must be used in this form rather than another as it is with mustn't and don't have to?
  2. Is there a negative form for may/might have that we should be aware of? If so I think it would be convenient to categorise modals on the aspects of perfect or simple and negative or positive cases 

Hello MinhLuu,

Modal verbs do not have a 1-1 correllation between form and function, so a single modal verb has multiple uses and a single meaning can be expressed by multiple modal verbs. Further, the uses of perfect forms of modal verbs do not necessarily match the uses of the equivalent non-perfect forms. For example, must can be used to express obligation and deduction:

must for obligation: I must finish the project by the end of the week.

must for deduction: She must be fit if she is running the marathon this weekend.

We can use must have for deduction:

She must have been fit if she ran the marathon last year.

However, we need to use a different verb for past obligation:

I had to finish the project by the end of the week.

Given all of these considerations I think to answer your questions clearly we need to see the context that you are thinking about. What use of might/may do you have in mind? Please provide an example as this will determine if might not (have)/may not (have) is possible or if another form is required.

 

Peter

The LearnEnglish Team

Submitted by HenryHtut on Tue, 24/06/2025 - 14:00

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Are there any official terms for those types of specific verb forms? As they are not included in the 12 tenses of English grammar, I wonder how they are called officially. I used to believe that can have, should have, etc. + V3 are parts of Future Perfect Tense, but it turned out wrong. For these reasons, I would like to know if they are any official terms for the verb forms described below:

  1. can do, could do, may do, might do, shall do, should do, would do, must do, etc.
  2. can be doing, could be doing, may be doing, might be doing, shall be doing, should be doing, would be doing, must be doing etc.
  3. can have done, could have done, may have done, might have done, shall have done, should have done, would have done, must have done etc.
  4. can have been doing, could have been doing, may have been doing, might have been doing, shall have been doing, should have been doing, would have been doing, must have been doing etc.

Hello HenryHtut,

Are there any official terms for those types of specific verb forms? As they are not included in the 12 tenses of English grammar, I wonder how they are called officially. I used to believe that can have, should have, etc. + V3 are parts of Future Perfect Tense, but it turned out wrong.

That's not how modern grammarians view English. English has two tenses only: past and present. Everything else is a combination of these with other grammatical elements of the verb such as aspect, voice, mood and modality. The present perfect continuous, for example, is not a separate tense but rather present tense with perfect and continuous aspects. It's a rather academic discussion but it is a much more accurate way to describe the language.

You can read more about this on our pages about present and past tenses:

https://learnenglish.britishcouncil.org/grammar/english-grammar-reference/present-tense

https://learnenglish.britishcouncil.org/grammar/english-grammar-reference/past-tense

And you can read in more detail about how the English verb system works here:

https://en.wikipedia.org/wiki/Tense–aspect–mood

 

For these reasons, I would like to know if they are any official terms for the verb forms described below:

can do, could do, may do, might do, shall do, should do, would do, must do, etc.

These are modal verbs followed by bare infinitives (the infinitive without 'to').

can be doing, could be doing, may be doing, might be doing, shall be doing, should be doing, would be doing, must be doing etc.

These are modal verbs followed by continuous infinitives.

can have done, could have done, may have done, might have done, shall have done, should have done, would have done, must have done etc.

These are modal verbs followed by perfect infinitives.

can have been doing, could have been doing, may have been doing, might have been doing, shall have been doing, should have been doing, would have been doing, must have been doing etc.

These are modal verbs followed by continuous perfect infinitives.

 

Peter

The LearnEnglish Team

Thank you for your reply. So what about the future tense? What I have learnt is that there are 12 tenses. Present and Past tenses that you refer to in the links are included in what I meant about 12 tenses. But one more thing is that I have also been taught about the future tense which have simple, continuous, perfect and perfect continuous aspects like below:

  1. will do (Future Simple Tense)
  2. will be doing (Future Continuous Tense)
  3. will have done (Future Perfect Tense)
  4. will have been doing (Future Perfect Continuous Tense)

By what you stated, in the official terms, they don't really exist, right? So am I right to assume that those tenses are described in some of the grammar books just to help the learners understand more easily about grammar? 

Thank you in advance.