Modals: probability

Modals – probability

Do you know how to use modal verbs and other expressions to show how probable you think something is? Test what you know with interactive exercises and read the explanation to help you.

Look at these examples to see how modal verbs and other expressions are used to show how certain the speaker is about something. 

She might well be on the train.
That must be his dad.
That can't be right.
You're bound to make mistakes occasionally.

This page focuses on expressing the probability of present and future situations. To learn how to express probability in relation to past events go to Modals – deductions about the past.
Try this exercise to test your grammar.

Grammar test 1

Grammar test 1: Grammar C1: Modals – probability: 1

Read the explanation to learn more.

Grammar explanation



We use must when we feel sure that something is true or think it's the only realistic possibility.

You must be tired. You've been travelling all day.
That must be Clare's house. I can see her car outside.

Note that we use must to show that we deduced this – we have arrived at this conclusion by reasoning.  

This must be her house. (I've arrived at this conclusion by reasoning or looking at the evidence.)
This is her house. (A simple statement of fact.)

be bound to

We can also use be bound to to express certainty about a guess or prediction.

There are transport strikes tomorrow, so travel is bound to be more difficult.
They are by far the best team – they're bound to win.

Be bound to is not a modal verb, but it is a related expression.


We use can't when we feel sure that something is not possible.

That can't be right, can it?
It can't be easy for him, looking after three kids on his own.

Degrees of uncertainty


We use should and shouldn't to show expectations about the future. They show we think something will probably be the case because it's normal or reasonable to expect. 

Rest and drink plenty of water. You should feel better in a day or two.
It shouldn't be a problem.

Should and shouldn't in this context have the meaning of 'if all goes well'. We don't use them to predict something negative or unwanted. 

The treatment should be very painful.
Our flight shouldn't arrive on time.

might, may, could

We use might, may or could to say that we think something in the present or future is possible but we're not sure. 

I might see you tomorrow if you're in the office.
There may be another issue that we don't know about.
This illness could be prevented.

They all have the same meaning, but may is more formal than might and could.

Adding well after the modal makes the situation sound more likely.

I'll try the pharmacy, but it might well be closed now.
She may well have to rethink her plan.
That could well be true.

The negative forms are may not and might not (or mightn't).

We may not need waterproof jackets, but I'll pack them anyway.
Safi might not come today as he has his driving test.

Couldn't is different from may not and might not. It means something is impossible.

General possibility


Note that can is not used to talk about possibility in relation to a specific event or situation. 

Azi can may/might/could be in the garden.

Instead, can shows that something sometimes happens or is capable of happening.

Noisy neighbours can be a problem if you're living in a flat.
It can be very cold here in winter.

Note that all modal verbs are followed by an infinitive without to.

Do this exercise to test your grammar again.

Grammar test 2

Grammar test 2: Grammar C1: Modals – probability: 2

Language level

Average: 4.8 (17 votes)
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Submitted by ivanskcheung on Sat, 10/02/2024 - 11:31


For Question 7 of the 2nd test, I chose "mustn't" as the answer. Although in "Show Answers", it has "can't" as the sole correct answer, I input both answers, including the sentences they are situated in, into Bing Chat, which found that both answers were grammatically correct, because according to Bing,
1. “He was here a second ago.”: This is a complete sentence. It has a subject (“He”) and a verb (“was”). The phrase “a second ago” provides additional context about the timing of his presence.
2. “He mustn’t be far away.”: This is also a complete sentence. The subject is “He,” and the modal verb “mustn’t” indicates a strong probability or necessity. The phrase “far away” describes the distance.
So, are the answers correct or is Bing correct?

Hello ivanskcheung,

This is a good example of the limitations of certain types of language models. The sentence is structurally correct but does not make sense in terms of meaning. The speaker is making a logical deduction: since he was here such a short time ago, it is impossible for him to be very far away now. We do not use mustn't for logical deduction and it does not fit the context here.



The LearnEnglish Team

Submitted by Basheer Ahmed on Mon, 27/11/2023 - 11:04



As it has been mentioned in the lesson that "CAN" can't be used for the sentences showing possibility. In this regard, there are two sentences,

She can perform at the concert tonight. (in the context of possibility)
She might perform at the concert tonight.

Which one is correct and which, not.

There is another question in my mind, confusing me a lot. I would be indebted to you if you could help me clarify its function:

She can't still be working.
You should be studying hard to pass the exam.

I have seen present participle used with CAN and SHOULD, at multiple places multiple times. Please highlight the purpose behind using progressive form of verb with MODAL verbs.

Thank you.

Hello Basheer Ahmed,

1) 'She can perform at the concert tonight' expresses the idea of ability. She is able to perform. There can be many reasons for this -- because she is in the city, because she has no other engagements, because she is healthy, etc. If we understand the word 'possible' to mean that the conditions are correct, then you could also say that this sentence expresses the idea of possibility.

But that is not what is meant in the explanation above when it says 'Note that can is not used to talk about possibility in relation to a specific event or situation'. When the explanation refers to possibility, it refers to the speaker not knowing for certain. When we are not certain, we use 'might'. Perhaps she has been ill for several days and so we aren't certain if she will be able to perform, or perhaps her flight into the city has been delayed and we aren't sure she will arrive in time. These are examples of us what the explanation refers to as possibility.

2) The use of the progressive form in the examples you provide are examples of the continuous aspect. If you follow the link, you'll see that we use the continuous aspect to communicate several different ideas. Which one is meant depends on the situation, but, for example, 'You should be studying hard' could mean that the speaker thinks you should study not just one day this week, but every day this week. The sentence 'You should study hard' is more general and provides less information. The continuous aspect communicates something extra, but what exactly that extra meaning is depends on the situation and how the speaker sees it. Normally the situation will make it clear.

Best wishes,
LearnEnglish team


Submitted by Sefika on Sun, 12/11/2023 - 09:41


"On Tuesday morning, Saudi Arabia's first official envoy to the Palestinians, Nayef al-Sudairi, who is also ambassador to Jordan, drove into the West Bank via the Karama crossing for a two-day visit. Israel controls entry at the border and would have had to have authorised his arrival."(

In the excerpt above, does the "Israel ... would have had to have authorised his arrival" part imply that Israel (had) authorised his arrival? Could it be an unconfirmed past fact? Could it mean "Israel probably (had) authorised his arrival"?
I would really appreciate it if you could/would help me with this?

Hello Sefika,

Yes, I think that's right. As far as I can tell, it means that the journalist did not have confirmation of this detail, but given the situation, assumed that it was true. 

Nice job interpreting that!

Best wishes,
LearnEnglish team

Submitted by DoraX on Fri, 06/10/2023 - 13:11


Hello LearnEnglish team,
Are the modals "should" and "might" alsο used for a request as in the following examples? "I should be grateful if you could translate it for me."
"You might post it for me, please." If yes, how common is this use nowadays both in spoken and in written English?

Hi DoraX,

Yes, "should" is used in that particular phrase: I should be grateful if ... . It's somewhat formal in style.

"Might" is sometimes used to make requests, but normally in the question form: Might I make a suggestion? Might you have time to help me with something? This is also rather formal in style.

I hope that helps.


LearnEnglish team