Probability

Learn about modal verbs for possibility, impossibility and certainty and do the exercises to practise using them.

Level: beginner

Possibility

We use may, might and could to say that something is possible, but not certain:

They may come by car. (= Maybe they will come by car.)
They might be at home. (= Maybe they are at home.)
If we don't hurry, we could be late. (= Maybe we will be late.)

We use can to make general statements about what is possible:

It can be very cold here in winter. (= It is sometimes very cold here in winter.)
You can easily get lost in this town. (= People often get lost in this town.)

Be careful!

We do not use can to talk about specific events:

A: Where's John?
B: I'm not sure. He may/might/could be
(NOT can) in his office.

Notice the difference in meaning between can and may/might/could:

That dog can be dangerous.
(= Sometimes that dog is dangerous. I know.)

That dog may/might/could be dangerous.
(= Perhaps that dog is dangerous. I don't know.)

can and may/might/could

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Level: intermediate

We use may have, might have or could have to make guesses about the past:

I haven't received your letter. It may have got lost in the post.
It's ten o'clock. They might have arrived by now.
Where are they? They could have got lost.

We use could to make general statements about the past:

It could be very cold there in winter. (= It was sometimes very cold there in winter.)
You could easily get lost in that town. (= People often got lost in that town.)

could and could have

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Impossibility

Level: beginner

We use can't or cannot to say that something is impossible:

That can't be true.
You cannot be serious.

Level: intermediate

We use can't have or couldn't have to say that a past event was impossible:

They know the way here. They can't have got lost!
If Jones was at work until six, he couldn't have done the murder.

Certainty

Level: beginner

We use must to show we are sure something is true and we have reasons for our belief:

It's getting dark. It must be quite late.
You haven’t eaten all day. You must be hungry.

We use should to suggest something is true and we have reasons for our suggestion:

It's nearly six o'clock. They should arrive soon.

Level: intermediate

We use must have and should have for the past:

They hadn't eaten all day. They must have been hungry.
You look happy. You must have heard the good news.
It's nearly eleven o'clock. They should have arrived by now.

Probability 1

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Probability 2

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Probability 3

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Probability 4

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Probability 5

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Submitted by ashki_ikhsa on Thu, 12/01/2023 - 08:55

Hello,

In the example:"It's nearly eleven o'clock. They should have arrived by now." which meaning can be inferred? Can either meaning be inferred based on the context?
1. The speaker expects them to be there(a known place) now, but they are not (the speaker expects something that didn't occur)
2. The speaker believes they should/must be there(a known place) now, but he/she doesn't know whether they've arrived or not?

Hello ashki_ikhsa,

Great question! Both of these meanings are possible. As you suggest, usually the context will make it clear which one is intended.

All the best,
Kirk
The LearnEnglish Team

Submitted by Ananije on Wed, 16/11/2022 - 22:52

Hi.
I was wondering what is the difference between these 2 sentences if I had to compare them and paraphrase them:
1. It cant be true.
2. It may not be true.

I think second one is clear to me. It expresses possibility. It may be true or may not be true. We're not sure.
First one I think is expressing disbelief but I don't think that's a valid explanation or use. So what can I say about it?

Thank you.

Hi Ananije,

As you say, the second sentence expresses possibility: there is a chance that it is not true, but also a chance that it is true. There is no indication of the degree of likelihood here.

The first sentence (don't forget the apostrophe: can't) expresses disbelief, as you say. The speaker cannot believe something is the case. It is still a belief, not a fact, and so is a form of speculation but it is a firm belief. The equivalent for strong belief that something is true would be 'must': It must be true.

Peter

The LearnEnglish Team

Submitted by nhanvu01 on Sun, 10/07/2022 - 17:39

Hi, I just want to ask why the past event we need to use modal verb + have + v3?

Hello nhanvu01,

Ultimately, this is just the way English has developed, though consider that 'have' is used to indicate the perfective aspect in other situations.

I'm sure someone specialised in the history of English linguistics could say a bit more about how this came to be, but I'm afraid I cannot!

All the best,
Kirk
The LearnEnglish Team

Submitted by fesquivel on Sun, 27/02/2022 - 23:22

I am confused about can and may/might/could for possibility, it says that can is for general and the rest for specific but if you say that "a dog is dangerous" it is very specific to me.

Hello fesquivel,

We use 'can' for possibility when the meaning is general. For example:

"Dogs can be dangerous."

If we are talking about a particular dog (a specific reference) then we use one of the other modals:

"Watch out for that dog - it might/could/may be dangerous."

I hope that clarifies it for you.

Peter

The LearnEnglish Team

Submitted by DaniWeebKage on Sun, 25/07/2021 - 16:02

Dear Team, 1) Where are they? They could be lost in the town. 2) Where are they? They could have lost in the town. What is the difference? Thanks you!!!

Submitted by Peter M. on Mon, 26/07/2021 - 06:30

Hello DaniWeebKage,

The second sentence is not correct.

Lost is a transitive verb, which means it needs an object. You can lose something (lose money, lose your wallet etc) or you can use a passive construction (be/get lost).

Peter

The LearnEnglish Team

Thank You!!! 1)Where is my book? It could be in the cafe. 2)Where is my book? It could have left in the cafe. Among the Aforementioned two sentences, The former is used when we are guessing what could happen in the present. The latter is used when we are guessing past action or sth( maybe affect the present). Is my summary correct? If not, correct me.

Hello again DaniWeebKage,

I'm afraid your second sentence here is also incorrect for the same reason: leave is a transitive verb in this usage so you need an object or a passive construction. The sentences should read as follows:

1)Where is my book? It could be in the cafe.

2)Where is my book? It could have been left in the cafe.

As far as the modal verbs go (which I think is the main focus of your question), your explanations are correct. We use could + verb to speculate about the present and could have + verb3 to speculate about the past. Well done!

Peter

The LearnEnglish Team

Hello! I read this explanation and now I'm a bit confused because it says above that we use could+verb to make general statements about the past. I've always thought that it's used to speculate about the present (except when we talk about past ability o with verbs of the senses), just like you say in this comment.
Are these two different usages? Thanks in advance!!

Hello Victoria7,

You're correct that these are different uses.

• We can use could + verb to speculate about the present: She could be lost. Maybe we should help?
• We can also use could + verb to make general statements about the past: When I was a child you could count on the trains arriving on time.

Modal verbs have multiple uses and there is no 1-1 correlation between verb and use. One verb can have many uses, and each use can be expressed by multiple verbs.

Peter

The LearnEnglish Team

Submitted by Selet on Tue, 23/02/2021 - 16:36

Hi Peter M. I see you using 'could in your comments when replying user questions. Is 'could' used to make a suggestion and means be able to? We can use the definite article in several ways. When you say 'the bus' it could mean a particular bus (Look - the bus is coming!) or it could have a general meaning and refer to the means of transportation (I prefer the bus to the train). Second, can I say 'it may mean...'/'it may have'...? If so, is there any difference of meaning?

Submitted by BobMux on Thu, 24/12/2020 - 06:02

Hello The LearnEnglish Team! Could you please help me understand better the difference between "can" and "might, may and could" when we are using them to express possibility?

Hello BobMux,

This is a very general question which requires contextualised examples. Perhaps you can provide an example sentence to illustrate what you mean. This will help to clarify your question and also ensure that our explanation is clear for you.

Peter

The LearnEnglish Team

Hello there! I would like to know the difference in meaning of these two sentences: It can be dangerous to cycle in the city. It could/may be dangerous to cycle in the city.

Hello BobMux,

The sentence with 'can' speaks more about cycling in the city in general, i.e. at any time, in any situation, for any person. The sentences with 'could' or 'may' are more often used to speak about a more specific hypothetical time or situation in the future.

For example, let's say a friend of ours was cycling in the city and had an accident. We could say the first sentence as a kind of comment on how dangerous it is to cycle in the city after this specific event. The second sentence wouldn't work well in this situation -- it's more for a time we're thinking of that could happen in the future, for example, if we're thinking about whether we should take our children cycling in the city tomorrow.

I hope this helps you make more sense of it.

All the best,

Kirk

The LearnEnglish Team

Hello Kirk, It was rather useful your explanation and thanks a lot. But i am still a bit confused. I would be really happy if you were able to help me understand better modal verbs: In a book it is said that the modal verbs "might", "may" and could are used to express both possibilty and make a guess. This words is given " this rush might/could/may be a symptom of something more serious". So here is it possibility or making a guess? And how can i distinguesh between possibilty and making a guess?

Hello BobMux,

Modal verbs are used in a number of ways, which can make understanding them a little challenging. It's really difficult to summarise these uses in a few posts here, but I will try to help you here. Please know, though, that you'll probably need to spend some time noticing them in different contexts (ideally as you read text or listen to speech) to really understand them well.

I'm not sure exactly what the difference between 'possibility' and 'a guess' are -- these can be defined in different ways. But generally speaking, I'd say 'may' and 'might' are expressions of the speaker's uncertainty about something. If we say 'The bus may be late', we are guessing but don't really know. In a way, this is also saying that it's possible for the bus to be late, though.

'could' can express the same idea of the speaker's uncertainty. Being related to 'can', it can also express the idea of potential, but again, in this context, I'm not that really means anything too different.

I hope this helps you.

All the best,

Kirk

The LearnEnglish Team

Submitted by ahmed16 on Sun, 01/11/2020 - 11:51

Dear teahcers, 1- Why can't we use " can have " to make guesses about the past like may have, might have or could have ? 2- Why can't we use " couldn't " to say that something is impossible like " can't " ?

Hello ahmed16,

I wish that it were a bit more logical, but I'm afraid this is just the way that English has developed as people have been speaking it over the last several centuries. There are some technical analyses of modal verbs that can help understand how they work a bit better, but I'm afraid they require a bit of study to make sense of and are well beyond the scope of what we do here.

Best wishes,

Kirk

The LearnEnglish Team

ok Do you mean that it is a language and its rules must be adhered to, even if what I am saying is relatively true?

Submitted by Kirk on Mon, 02/11/2020 - 10:24

Hello ahmed16,

If you want to be understood by others, then yes, you generally have to follow the rules that other people follow when speaking. There are ways to break the rules and still be understood, but in my opinion it's important to learn the rules most people use first.

Hope this helps.

All the best,

Kirk

The LearnEnglish Team

Submitted by ahmed16 on Sat, 31/10/2020 - 23:43

Dear teachers can we use " can have " to make guesses about the past like may have, might have or could have ? A second question can we use " couldn't " to say that something is impossible ?

Hi ahmed16,

Good questions! I'll answer them in order.

1. No. We can't use can have, but we can use the negative form can't have to show that we think it's not possible that something happened. Have a look at this page on Modals for deductions about the past for more examples and explanation.
2. We can use couldn't have to say that something was impossible (in the past), but we can't use couldn't on its own with this meaning. See this page on can and could for more information.

Does that make sense?

Jonathan

The LearnEnglish Team

Submitted by iamsashafierce on Tue, 13/10/2020 - 10:26

Coul you help me, please? Can we use OUGHT TO instead of SHOULD in these particular cases? 1. They insisted that we should have dinner together. 2. It is essential that everyone should be here on time. 3. It is strange that he should be late. He is usually on time. 4. If it should rain, take an umbrella with you. 5. It is cold outside. I should wear a coat (like advice).

Hello iamsashafierce,

We don't use ought to in place of should in conditional structures (#4) or as an alternative subjunctive form (#1, 2, 3), so only in the last sentence (#5) can you replace should with ought to.

Peter

The LearnEnglish Team

Submitted by OlaIELTS on Sun, 20/09/2020 - 23:34

This tip is really interesting. Thanks.

Submitted by IsabelTim_123 on Tue, 08/09/2020 - 18:16

I reluctantly agreed to a postponement on condition that the sale should be completed and the boat handed over by 31st August. You may borrow the book on condition that you return it tonight Teacher, why is "should" used in 1st sentence but not in 2nd sentence? Thanks for your reply in advance.

Hello IsabelTim_123,

Personally, I wouldn't use 'should' in that sentence -- I'd just say 'be'. I wouldn't say it's wrong there, but it does strike me as redundant. If you check example sentences in dictionaries, I doubt you will see 'should' used in similar sentences.

All the best,

Kirk

The LearnEnglish Team

Submitted by Abhishek on Fri, 31/07/2020 - 16:28

It's ten o'clock. Dad might have finished his work. Or It's ten o'clock. Dad might have finished his work. Which one is correct ? Or Both are correct ?

Hello Abhishek,

Peter

The LearnEnglish Team

Submitted by Ana Silvo on Wed, 27/05/2020 - 09:52

Dear teahcers, Can you explain what is difference between may have, might have or could have? Namely, I want to know difference between them like your explanation about ' may, might and could ' in first paragraph. Thanks a lot in advance

Hello Ana Silvo

There's no difference in meaning between them. 'might' is a little more common in speaking and 'may' a little more in writing, but people often say 'may' and often write 'might'.

Note that each of these modal verbs can be used in other situations, and in some of those situations, they don't mean the same thing. But here in the context of probability they do.

All the best

Kirk

The LearnEnglish Team

Submitted by Amit shukla on Mon, 11/05/2020 - 05:38

Sir, can I use modal verbs for future like "He may have gone by tomorrow 2.00 PM."

Hello Amit shukla

Yes, that sentence is grammatically correct, though I would recommend thinking of 'may' as expressing possibility more than the future.

Please note that when you post a comment, it is not published right away. Please don't post the same comment twice; we'll be able to respond more quickly!

All the best

Kirk

The LearnEnglish Team

Submitted by Rany on Fri, 28/02/2020 - 19:26

Hi teacher, I have one sentence about possibility in the past and I just want to know if it’s right or wrong “ His math may have improved by the time the exam came “ Thank you .

Hi Rany,

The sentence is perfectly fine. It tells us that the speaker does not know if the person's maths improved or not, but that it was possible. The meaning is the same as might have and could have in this context.

Peter

The LearnEnglish Team

Submitted by aria rousta on Fri, 06/09/2019 - 16:16

Dear sir We all know that modals have not indicate tenses, and they only reflect four different aspects of simple, continoues, perfect and perfect continoues. Base of this assumption why in some parts you keep saying this modal use for past certainty, for example they must have practiced too much. But at this example we can not say it is only reflect past tense, it might refer to future or present base on the time phrase used with it , for example For future, they must have practiced well by tomorrow morning. For present, they must have practiced well by now. For past, they must have practiced well already. Would you please tell me if i am thinking in a right way. Sincerely Aria

Submitted by Peter M. on Sat, 07/09/2019 - 07:59

In reply to by aria rousta

Hello Aria,

Modal verbs have a range of meanings. When 'must' is used for logical deduction it is always a deduction following another action, so the only way to use it in a future context is to create an future condition. You cannot say 'They must have practised well by tomorrow morning' but you could say 'If they win the game tomorrow then they must have been practising hard'.

Note that 'must have' can also be used with other meanings. For example, when we use 'must' for obligation we can use it with future reference. For example, you could say 'When I get back to the office you must have finished this project or there will be trouble!'

Peter

The LearnEnglish Team

Submitted by sam61 on Wed, 30/01/2019 - 11:04

I couldn't care less about that. Is this the second conditional without the condition or does it refer to the past modal for ability? Is it ambiguous? Is it the modal for possibility rather than ability? Can it be both?

Hi sam61

Without knowing the context, it's impossible to say which meaning is intended, because both are possible. Normally the context should make it quite clear.

All the best

Kirk

The LearnEnglish Team

Submitted by jitu_jaga on Tue, 03/07/2018 - 23:12

Hi, A-do you remember me? B-how could I forget you? In the second sentence 'could' is used for ability or possibility and which time it refers (present/past/future). Please explain?

Submitted by Peter M. on Wed, 04/07/2018 - 07:14

Hi jitu_jaga,

I think we've already provided a lot of explanations on this point and can't really continue explaining the same point with yet more examples. Why don't you tell us what you think the meaning is here and we will comment on your idea?

The important thing is not which label (possibility/ability etc) you put on a word, but rather that you understand how it is used in communication.

Peter

The LearnEnglish Team

Submitted by jitu_jaga on Mon, 25/06/2018 - 11:53

Hi, 1.How could you do that to me? Here, in this sentence 'could' is used for ability or possibility? and which time does this sentence refer(present/past/future)? 2. What is the difference between possibility and probability?

Submitted by Kirk on Mon, 25/06/2018 - 16:01

Hi jitu_jaga,

It's difficult to say for sure without context, but it looks to me as if 'could' is being used to express past, or perhaps hypothetical, ability in the sentence you ask about. If I found out that a close friend of mine planned to borrow my car without asking my permission, for example, I might say something like this. The idea is that a good friend wouldn't be able to hurt me in that way.

'possibility' refers to whether something could happen or not; 'probability' refers to how likely it is that it could happen -- it's like the level of possibility of something. The lottery is a classic example -- it's not probable that you win the lottery, but it is possible.

All the best,
Kirk
The LearnEnglish Team

Submitted by QaaZee on Sun, 24/06/2018 - 22:52