Modal verbs of obligation — must, should, have to

Modals of obligation are modal verbs in English that express that a certain action is necessary, required, or recommended depending on the situation, rules, laws, or someone’s personal opinion.

In this article, we’ll explore how to use the main modals of obligation — must, should, and have to — and practice using them in real-life contexts.

Contents

1. What are modal verbs of obligation in English?
2. Main modals of obligation: must, should, have to
     2.1 Should
     2.2 Must
     2.3 Have to
          2.3.1 Don't have to
3. Other modal verbs expressing obligation
     3.1 Need to
     3.2 Ought to
4. Practice Exercise
5. FAQs

What are modal verbs of obligation in English?

Let’s first look at how sentences with modal verbs differ from those without them.

• Anyway, you must wear a helmet when you ride a horse.
• I have to wear a uniform at work.
• Christina should see a doctor immediately.

Now, try to imagine these sentences without the highlighted modal verbs:

• Anyway, you wear a helmet when you ride a horse.
• I wear a uniform at work.
• Christina sees a doctor immediately.

As you can see, the meaning of the sentences changes dramatically. Now these actions sound voluntary, regular, and free of any obligation, advice, or recommendation. That’s why if you want to give a friend (or yourself) some advice, explain workplace rules to a new colleague, or talk about something that must be done — these verbs are absolutely essential.

And if you’d like to explore modal verbs in more detail, be sure to check out our other articles on the topic:

• Modals of Willingness
• Modals of Probability
• Modals of Deduction
• Modals of Ability
• Modals of Advice
• Modals of Permission

Main modals of obligation: must, should, have to 

The most well-known and commonly used modal verbs of obligation are:

• Should
• Must
• Have to

Each of these verbs has its own specific meaning, which we’ll explore in the next section.

Should

Should doesn’t have a clear one-to-one translation into Ukrainian. Should не имеет четкого дословного перевода с английского. It is used when someone gives a recommendation, advice, or expresses hope that the other person will follow it.

• You should spend more time outdoors instead of sitting in front of your laptop.

Should can also be used when talking about moral or ethical duty:

• You should apologize because it’s only you who made this mess.

Keep in mind: should doesn’t express obligation as strongly as must or have to. It sounds softer and allows more room for personal choice.

The structure for affirmative, negative, and question forms with should is as follows:

Must

Some modal verbs in English can have more than one meaning. Let’s look at them in more detail. Must in English is used to

• Show strong obligation or necessity to perform an action because of someone’s personal conviction:

I must eat more vegetables, because I want to be healthier.

• Give emotional advice or encouragement;

Marusia must study harder!

• Make a logical conclusion or deduction;

Daddy has been working all day, he must be so tired.

The general sentence structure with must looks like this:

Keep in mind, that in the negative form, must changes its function and expresses a strong prohibition — something that is not allowed.

• You mustn’t park here. (It is strictly forbidden)

Have to

Many students get genuinely confused when learning about modals of obligation, especially when trying to tell the difference between have to and must. This happens because in their native language, there’s often no clear distinction between such verbs. Have to, unlike must, expresses obligation or necessity that comes from outside — from rules, laws, or someone else’s will — not from the speaker’s personal belief. For example:

• Children have to wear uniforms at our school.
• Bohdan had to stay at home because his mother asked him to.

In these examples, both the children and Bohdan are required to do something regardless of their own desire.

Keep in mind: have to is also called a semi-modal verb. We’ll look at the key differences in the following table.

Don't have to

In the negative form, have to expresses the absence of necessity to do something. In other words, the action is not required — you can do it if you want to, but it’s not necessary.

• You don’t have to pay for the dinner. (You’re not obligated to pay — but if you insist, you can.)
• Nazar doesn’t have to wake up early tomorrow morning. (It’s not necessary — but if he wants to, he can.)

Keep in mind that in negative sentences with he/she/it, you need to use doesn’t, not don’t.

Other modal verbs expressing obligation

Above, we discussed the most commonly used modal verbs — must, should, and have to, but there are two more that are also worth mentioning:

• Need to
• Ought to

Need to

Need to expresses necessity or obligation, but in a more neutral tone. It often reflects a requirement based on circumstances, common sense, or practical need.

It’s frequently compared to have to and is widely used in everyday conversation when you want to avoid sounding too strong or forceful.

• We have run out of milk, we need to go to the supermarket.

Ought to

Ought to is used to express moral obligation, advice, or an expected right action. It has a similar meaning to should, but sounds more formal.

•    You ought to add more convincing arguments to your presentation.

Pay attention: in questions, particle to is separated from the modal verb ought.

✗ Ought to I apologize?
✓ Ought I to apologize? 

Keep in mind: in modern English, this form is rarely used. Ought to is more often replaced by should.

Practice Exercise

Time to practice! Complete this short exercise to check your understanding of modal verbs of obligation. Choose the correct sentence:

FAQ

1. What are modals of obligation? (with examples) 

2. What’s the difference between must, should, and have to?

• Must expresses internal obligation — a strong need to do something, often close to a command. Sometimes, it can also be used to give emotional advice.
• Have to is used when the obligation comes from external sources, such as rules, laws, or specific circumstances.
• Should is used for advice or recommendation, without strong necessity.

Examples:

• I must finish this report today. (I’m telling myself I have to do it — internal pressure.)
• I have to wear a uniform at work. (My employer requires it — it’s a rule.)
• You should take a break at least for 10 min. (It’s a good idea, but not something you’re forced to do.)