Understanding “Must”

The word “Must” is a modal verb in English. Modal verbs are auxiliary verbs that provide additional and specific meanings to the main verb of the sentence. The word “Must” is used to express an obligation, necessity, or a strong suggestion.

Usage of “Must”

Obligations and Duties

The most common usage of “Must” is to state obligations, duties, or requirements. This is when something is necessary or essential to do. For instance:

    • I must finish my work before the weekend.
    • You must submit your assignment by tomorrow.


“Must not” (often contracted to “mustn’t”) is used to express prohibition — something that is forbidden to do. For example:

        • You mustn’t smoke in a petrol station.
        • He mustn’t disturb the meeting.

Necessity or Strong Recommendation

Another use of “Must” is to indicate that something is necessary or highly recommended. It is often used to give strong advice. For example:

        • You must take some rest; you look very tired.
        • We must be there on time.

How to Form Sentences using “Must”

“Must” is always followed by a base verb (the infinitive form of the verb without “to”) regardless of the subject in the sentence. Unlike some other verbs, “Must” doesn’t change according to tense or the number or person of the subject. Here’s how to create sentences with “Must”:

Affirmative Sentences

In an affirmative sentence, “Must” is followed by a base verb. For example:

        • The children must tidy their rooms.

Negative Sentences

In a negative sentence, “Must” is followed by “not” and a base verb. For example:

        • He must not disobey his teachers.


In questions, “Must” comes before the subject and is followed by a base verb : Must + subject + base verb + …. ? For example:

        • Must we leave early?

Common Misconceptions and Problems with “Must”

Confusion between “Have to” and “Must”

One common issue English learners face is distinguishing between “Have to” and “Must” as both can suggest obligation. The key difference is that “Must” implies an internal obligation (personal judgment or a strong necessity), while “Have to” suggests an external obligation (rules, laws or other people). For instance:

        • We must eat healthy food (personal judgment).
        • We have to follow the traffic rules (external regulation).

“Must” in the Past Tense

Another common problem is using “Must” in the past tense. “Must” is a present tense verb. For past obligations and deductions, we use “Had to” or “Must have” respectively. For example:

        • I must go to the hospital (present necessity).
        • I had to go to the hospital (past necessity).
        • She must have been very happy (past deduction).

Practice Exercises:

You can practice using “Must” in your English sentences by trying these exercises:

        • Write a list of five things you believe you must do every day. Use the word “Must” to express personal obligations.
        • Choose a set of rules, like traffic rules or school rules. Use “Must not” to rewrite these rules in the negative form.
        • Think about a strong recommendation you would give to a friend about a book, movie, or restaurant. Use “Must” to express this recommendation.

With practice, understanding the meaning of “Must”, and its usage in different contexts will become second nature. Always remember that it is used to express obligation, prohibition, necessity or a strong recommendation. Happy learning!

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