How to use English Modal Verbs | Possibility & Probability

Can. Could. May. Might. Shall. Should. Will. Would. Must

Hey our English learners! Do you know what type of words these are? They’re modal verbs.

Recently, Learn English Fun Way team have been getting lots of questions about modal verbs from readers. Therefore, in this writing, we are going to share some useful tips to help you use them a little more effectively when you’re speaking English.

These modal verbs are auxiliary verbs, just like be, do and have because they work together with a main verb.

You always have a modal verb with a main verb and the main verb that follows is always in the bare infinitive form – without to.

Form: Modal verb+ V_bare

For example:

  • I could go..
  • You should take…
  • They would like…
  • Paul may borrow…

These modal verbs are used in English to express something. They have a purpose, and we need to try and understand that purpose today.

They can be used to talk about possibility and probability. To talk about how likely something is.

You can use these modal verbs to express how likely it is that that action will happen? Are you certain? If you’re sure, you’re confident that will happen, you can say:

  • It will happen.

Is it probable? Is it likely to happen? Is there a good chance it will happen?

  • It should happen.

Is it possible?

  • It can happen.

Or is it unlikely?

  • It couldn’t happen.

In all of these situations, you can use a modal verb to explain how certain you are that something will happen, how possible something is. Besides, these same modal verbs can also be used to explain ‘ability’– how able you are to do something. They can be used to ask permission, make requests and offer help.

There are quite a few different uses, so wwegoing to split this lesson in two so that you will not feel overwhelmed and confused. Let’s just take one step at a time.

In this lesson, we are going to teach you about how we can use modal verbs to talk about three main purpose: certainty, probability and possibility. So, these are three differen levels how likely something is about to happen.

And the next lesson will focus on ability and the other uses. So, try not to worry about them right now.

Now, let’s get started!

How to use English Modal Verbs | Possibility & Probability

I) Probability

Now, let’s start with probability, how likely something is to happen.


We use ‘will’ to talk about the future, when we’re confident that something will happen. We believe it. We’re certain it’s true.

  • The sun will rise tomorrow. => (I’m) pretty sure that will happen.
  • Ashley will be late. => She’s always late so I definitely believe that to be true!
  • If you don’t take a jumper, you will get cold. It’s freezing out there!

You’ll also hear ‘will’ used to give reassurance when you want to confirm that something is true.

  • “You will pass the exam. Don’t worry!” – My mum told me.
  • She’s using ‘will’ to tell you that she’s confident, she believes in you.
  • “It will be okay”- my friends told me.
  • They’re confident, they believe that everything will be okay.

Now, if you’re certain that something is not going to happen, use ‘will not’ or’ ‘won’t’.

  • If they walk, they won’t arrive in time. It’s too far!
  • I’m certain that that won’t happen.

How to use English Modal Verbs | Possibility & Probability

2, Must

We also use ‘must’ when we are confident and sure of something that is happening in the present. And usually we have a reason or an explanation to tell us why something is happening.

  • The baby’s crying. He must be hungry.
  • I thought Sarah would be here by now. She must be stuck in traffic.
  • They didn’t eat any of the meat. They must be vegetarian.

Notice how we’ve given a reason for all of these examples to show why we believe something to be true, and it’s quite common when you’re using ‘must’.It explains that you are quite confident about the statement and you’re able to give a reason to explain why you’re so sure.

You can use ‘must’ to talk about the past when you’re quite sure that something happened, then use ‘must have’.

  • After flying for 36 hours, you must have felt exhausted.
  • I thought I’d do better in the exam. I must have been really nervous.
  • Jack’s not here right now. He must have thought that you were meeting him downstairs.

See how this creates the perfect tense. The main verb following ‘have’ is in the past participle form.

So when talking about the present or the future, ‘must’ is followed by the bare infinitive form but when talking about the past, ‘must’ is followed by ‘have’ and the past participle verb form.

  • Present/ Future: Must + Vbare
  • Past: Must + have Vpp

And this pattern is true for many of the modal verbs that we’ll talk about today.

How to use English Modal Verbs | Possibility & Probability

3, Should

We use ‘should’ to say that something is likely. We’re not a hundred percent certain but we believe it to be true.

  • They left an hour ago, they should be here by now.
  • If they take the car, they should arrive by three.

To talk about the past, we use ‘should have’. It’s the same pattern.

  • I didn’t realise he was unwell. We should have offered to take him to the doctor.
  • The school knew Sam was going to be late. They should have called her mother.

How to use English Modal Verbs | Possibility & Probability

II) Possibility

1, Can

So if you’re making really general statements about something that is possible, use ‘can’.

  • People can be really rude.
  • Be careful because it can be quite dangerous on the streets at night.
  • It can be really hard to find a speaking partner to practise English with.
  • It can take over twelve hours to hike through those mountains.

These are all general statements, they’re not specific. It is said these statements are possible but it is not said exactly what is happening.

In this context, ‘could’ is used as the past tense of ‘can’.

  • I remember winters in London. Weeks could go by without ever seeing the sun!

How to use English Modal Verbs | Possibility & Probability

2, Could- May- Might

When we’re uncertain or unsure about the present and the future, we use the modal verbs ‘could’, ‘might’ and ‘may’. They explain that something is possible but not certain or guaranteed.

  • If you wait near the door on Lewis Street, you could see the Prime minister leaving.
  • They might arrive before lunch, but I’m not sure.
  • I may need to borrow your car.

‘Might’ and ‘may’ here are very similar.

There is a very slight difference between the two, in that ‘might’ tells us that the outcome is a little bit less likely. But the truth is that ninety-nine percent of native English speakers don’t even realise this. So you don’t need to worry about the difference at all. When used in spoken English, you can use either when talking about possibility. Just consider them to be the same.

  • We may go on a holiday in September.
  • We might go on holiday in September.

The meaning of this sentence is so similar but the second one suggests that it’s a little less likely.

We can also use ‘could’ to explain that we are uncertain or unsure about the future.

  • It could rain this afternoon.
  • It might rain this afternoon.
  • It may rain this afternoon.

All of these sentences tell us that it’s possible but not certain. There is a chance that it will happen.

  • Simon could arrive before us.
  • Simon might arrive before us.
  • Simon may arrive before us.

These examples all talk about the present or the future. And the modal verb is followed by the bare infinitive verb form. However,  if you want to talk about the past. Then we use these same modal verbs with ‘have’ followed by the past participle verb, so suddenly we’re using the present perfect tense.

  • Present/ Future: Could/may/might + Vbare
  • Past: Could/may/might + have Vpp

For example:

  • They might have finished dinner by now.
  • I’m worried. Something could have happened to Sara.

How to use English Modal Verbs | Possibility & Probability

III) Impossibility

We have mentioned about possibility above, now, let’s focus on impossibility – when something is not possible, when we know that something is unlikely to happen, the chances of it happening are really, really, really small.

When we think that something is impossible, we use the negative forms of ‘can’ and ‘could’. It means in these cases, we will use “can’t” or “couldn’t”.

  • You can’t be serious! It’s not possible. I don’t believe you!

=> This expression is often used after someone says something that you just don’t believe. When we think that what is said is very unlikely to be true.

  • When we told them they’d won, they couldn’t believe it!
  • He said he was in a band called ‘Meatball’! He couldn’t have been serious.

So when spoken, these negative forms are usually contracted:

  • Can’t. Couldn’t. Couldn’t’ve.

Especially, you will never see this last one written as a double contraction but you will hear it spoken.

In some cases, you will hear people pronounce the full negative form especially to add emphasis, or to make the meaning stronger.

  • That cannot be true!

You can make it even more dramatic by stressing every single word.

  • That can not be true!

How to use English Modal Verbs | Possibility & Probability


  • It is gonna be the end of the writing today. Let’s summarise now!
  • If you are certain about something use ‘will’ or use ‘won’t’ if you are certain that something is impossible.
  • If you’re confident about something and you have a reason for believing that, use ‘must’ or ‘should’.
  • If you’re talking about something generally that’s possible, use ‘can’.
  • If you are not certain but it’s possible, use ‘might’, ‘may’ or ‘could’.

So remember that there are different meanings for all of these modal verbs and we’re going to talk about these more in the next lesson.

We hope that you enjoyed that lesson! Hope you feel a little more confident using modal verbs to talk about possibility and probability.

In the next article, we will talk about how these modal verbs can be used for ability, to ask for permission, to give suggestions and ask for advice. But for now, keep practising with this lesson  and we will be back again next week with a new lesson for you.

In order to get further explanation and practice your listening skills also, watch the video below. Thank you for reading and see you in the next writing!

Credit: Youtube Channel “mmmEnglish!”


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