38 Modals of Obligation - Must

Must is an auxiliary modal verb used to express strong obligation due to personal opinion or authority.

In order to express prohibition when something is not allowed, we use Negative form of Must.

We usually find this structure in its three forms:

Affirmative

The Affirmative form of the verb Must has this structure:
Subject + must + verb.*

Negative**

The Negative form of the verb Must has this structure:
Subject + must + not + verb.*

**The Negative form usually expresses prohibition.

Interrogative

The Interrogative form of the verb Must has this structure:
Must + subject + verb + (?).*

*The form is always the same, even for the third person.

Must

1. Certainty/reasonably expected
   • It must be her encyclopaedia. Her name is written on the front page.
   • She must study hard, she has good grades.
   • They must be smart. NASA offered them internship.
2. Strong obligation
   • I must pass an oral exam.
   • She must pay the enrollment fee, it is obligatory.
   • We must attend the theory class this friday.
   • Must we attend the theory class this friday?
3. Necessity
   • I must do my internship.
   • He must take notes during the class.
   • They must attend the conference.
   • Must he take notes during the class?

Must Not

1. Prohibition
   • You must not spend your grant to alcohol!
   • He must not underline the sentences in this book. It belongs to the library.
   • They mustn’t enter the multimedia classroom.

Must is used to express obligation that comes from the speaker. We use Must when:

1. We are sure about something or something is reasonably expected (Affirmative);
2. There is strong obligation (Affirmative, Interrogative);
3. Something is necessary (Affirmative, Interrogative).

We use Must not when:

1. Something is prohibited.

We use the modal verb Must to express strong obligation due to personal opinion or authority. Must can be expressed in the three forms (Affirmative, Negative and Interrogative).

• Affirmative: Subject + must + verb (e.g. I must take);
• Negative: Subject + must + not + verb (e.g. I must not take);
• Interrogative: Must + subject + verb + (?) (e.g. Must you take…?).

For example:
— “She must be ill because she is coughing.“= The speaker is sure that she is ill.
— “I must visit my parents soon.“= The subject feels obligation about visiting her parents.
— “You must find a flat in Valencia.“= It is necessary for the subject to find a flat.
— “You must not beat your siblings ever again!“= The person is prohibited from beating his/her siblings.

Let’s revise this content within the [Form] section. Take a look at the [Example] section that shows its use within a context.