The modal verb must

Learn how to use the modal verb must efficiently. Register for free in the ABA English course to learn English in a practical and fun way and join the more than 30 million students worldwide who have trusted us.

START FOR FREE

What is and when is must used in English?

The modal verb must is an auxiliary verb used together with an infinitive verb to express obligation or prohibition. So, when is must used? We use it after any personal pronoun when we want to talk about obligations, duties, advice, or strong necessities. It can appear in affirmative or negative form.

With ABA English’s innovative video lessons, you will learn the characteristics of the modal verb must and each content of English grammar through simple explanations.

+30 MILLION STUDENTS

Join the largest digital English academy
in the world and learn English

START FOR FREE

WHY IT IS ESSENTIAL TO LEARN MODAL VERBS

Within English grammar we can find a wide variety of structures, among them, the modal verbs, which are auxiliary verbs used to express possibility, ability, obligation, or permission. This topic and many other contents are part of grammar, which will help you to understand each structure of the languageso that over time you can apply them correctly and manage the language fluently.

HOW TO USE THE MODAL VERB MUST

Here you have examples of sentences with must which can help you understand its use.

Modal verb must in affirmative

Must to express a moral duty.

‘You must respect older people.’

(‘You must respect older people.’)

Modal verb must in negative

Mustn’t to express prohibition. Must not is used in more formal contexts.

‘Students mustn’t smoke at school.’

(‘Students must not smoke at school.’)

Modal verb must in affirmative

Must to express obligation.

‘We must wear uniform at school.’

(‘We must wear uniform at school.’)

ABA ENGLISH VIDEO LESSONS WILL HELP YOU WITH ENGLISH GRAMMAR

The ABA English video lessons are a fundamental resource for you to understand, through easy and enjoyable explanations, all the structures that make up English grammar. Our best teachers will give you the explanations you need so you can understand and then use the structures and communicative functions you learned in each unit of the course. You can watch the video lessons as many times as you want and with the option to activate subtitles in your language or in English, so you don’t miss anything.

Differences between must and have to

Generally, have to refers to an external obligation, such as a law or a rule that if you don’t comply with it may have consequences. See the following examples:

You have to get a visa in order to enter the United Kingdom. (‘You have to get a visa in order to enter the United Kingdom.’)

I have to do my homework or else my mom will tell me off. (‘I have to do my homework or else my mom will tell me off.’)

In the negative sense, have to is subtler than must, and means that you are not obliged to do something or that it is not essential.

You don’t have to pay for the entrance. The fee is voluntary. (‘You don’t have to pay for the entrance. The fee is voluntary.’)

Usually, must is used when you acquire an internal obligation, by your own will, to do something.

If you ever travel to Paris, you must see the Eiffel Tower. (‘If you ever travel to Paris, you must see the Eiffel Tower.’)

They must think something is wrong. (‘They must think something is wrong.’)

When to use must not

You can use must not to say that something is prohibited or not allowed. You can contract it as: mustn’t. See some examples:

You must not step on the grass. (‘You must not step on the grass.’)

He mustn’t spend so many hours on the computer. (‘He mustn’t spend so many hours on the computer.’)

She mustn’t work tonight. (‘She mustn’t work tonight.’)

Do you know your
English level?
Take a test now.

Register on our page and access the level test for free. In a few minutes, you will know your level and be able to keep advancing with the course.

START THE TEST

Use of must have

You can use the modal verb must with the auxiliary verb have to talk about things that should have been done, or could have happened in the past. You can contract it as: must’ve.

It must’ve been love, but it’s over now. (‘It must have been love, but it’s over now.’)

What was that sound? – It must have been a cat. (‘What was that sound? – It must have been a cat.’)

Exercises with must

It is time for you to practice your knowledge of the modal verb must. Complete the following sentences accordingly:

He _______ _______ made a mistake. (‘He must have made a mistake.’)
You________ ____ wear casual outfits in the office. (‘You must not wear casual outfits in the office.’)
I ______ ______ a car so I can get to my job. (‘I must buy a car so I can get to my job.’)
You _______ _____ arrive late at work. (‘You must not arrive late at work.’)
She _____ take the children with her to Dallas. (‘She must take the children with her to Dallas.’)
It ______ ______ been raining there. (‘It must have been raining there.’)