How to Use Modal Verbs of Necessity: must, have to, need

You absolutely have to learn this! Without these modal verbs, you simply can’t express necessity or the importance of an action. And how else would you say “I really need a vacation” when deadlines are on fire? How do you express in English important things like: “I have to go to work” or “You should get more rest”? That’s where modal verbs of necessity come in. They help express obligation, need, advice, or rules. In this article, we’ll explore the key modal verbs of necessity, look at examples of how they’re used, and try out some practical exercises.

And if you want to delve deeper into the topic of modal verbs, we recommend reading our other articles:

• Modal Verbs of Willingness;
• Modal Verbs of Probability;
• Modal Verbs of Deduction;
• Modal Verbs of Ability.

Contents

1. Modal Verbs of Necessity: rules and examples
2. Must, Have to, Have got to
3. Need (to), Ought to, Shall
4. Exercises
5. FAQs

Modal Verbs of Necessity: rules and examples

So let’s get to it! There are several different situations where these verbs are used — something might be important personally to you, something else might be required by law or rules, and then there are just general needs. Let’s break it down more clearly.

We use these modals when we talk about:

• Obligation or duty
  You must attend the meeting.

• Rules or laws
  You have to wear a seatbelt.

• Moral advice
  You ought to be honest.

• Necessity
  You need to take a break.

• Formal promises or statements (in documents)
  I shall inform you tomorrow.

They often appear in business English, formal contexts, and everyday language when we talk about responsibility or the need to take action.

Must, Have to, Need, Ought to

If you’re still reading, that means learning English is definitely important to you — “I must learn these modal verbs!” And that’s exactly where we use must:

Must expresses a strong obligation, often moral or personal:

• You must apologize for being late.

The negative form — must not / mustn’t — expresses prohibition:

• You must not smoke here.

Must doesn’t have a past form, so we usually use had to for the past.

Now, if someone’s making you improve your English for work, then you’d say — I have to learn this.

Have to shows an obligation caused by external factors (laws, rules, requirements):

• I have to submit my taxes by April 15.

Have to changes with tenses:

• present: I have to go.
• past: I had to go.
• future: I will have to go.

Have got to is a conversational alternative to have to, especially in British English. It means the same but is used in the present tense:

• I've got to go now. (= I have to go now.) 

• Not used in past or future questions:
  ✗ Did you have got to...?
  ✓ Did you have to...?

Let’s compare:

• I have to work late tonight.
• I've got to work late tonight.

Both sentences mean the same (I have to work late tonight), but the second is less formal.

Need (to), Ought to, Shall

The simplest modal verb to express that you need something is need (to).

Need (to) indicates a requirement or necessity:.

• You need to drink more water.

In the negative, the construction looks like this:

• You don't need to worry.

Needn't is also possible, especially in British English:

• You needn't bring anything.

Аnd if you want to sound more formal, ought to is a great choice.

Ought expresses moral advice or expectation.

• You ought to respect your parents.
• You ought not to eat so much sugar.

The modal verb should is close in meaning to ought to, but it’s a less formal option and is more commonly used for giving advice

• You ought to submit the application by Monday. (slightly more formal)
• You should submit the application by Monday. (less formal, more like conversational advice)

For those dealing with documentation or official obligations, shall can come in handy.

Shall is used less frequently in the context of necessity, but it can express a formal obligation or decision — especially in legal documents or formal English.

• The tenant shall pay the rent on the first of each month.

It can also be used to express a suggestion or promise, especially in British English:

• Shall I open the window? (suggestion)
• I shall return by evening. (promise)
• Shall we summarise this article?

Modal verbs of necessity are a key tool in both everyday and professional English. Understanding the nuances between must, have to, need to, and ought to will help you sound clear, confident, and grammatically correct. Practice with exercises, pay attention to context — and soon these verbs will become part of your active vocabulary. So don’t skip the exercises below to reinforce the topic — it’s super important. You must do this!

Exercises

Task 1: Fill in the blanks with the correct modal verb. Choose between: must / have to / need to / ought to.

Task 2: Rephrase the sentence using the words in brackets.

FAQs

1. Is there a difference between “must” and “have to”?

Yes. Both are modal verbs of necessity. However, must usually expresses internal conviction or a strong moral obligation. Have to refers to an external obligation (e.g., a law or an employer’s requirement).

2. How do you say “must” in the past?

Use had to, since must does not have a past tense form.

• I had to cancel the meeting.

3. What does “don’t have to” mean?

This is another modal verb of necessity. It means that something is not required:

• You don’t have to come if you’re busy.

4. Which one should I use: “should” or “ought to”?

Both modal verbs are correct. Ought to sounds slightly more formal, but the meaning is the same: a suggestion, recommendation, or expectation.