Modal Verbs : Must (subjective obligation)

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We often use must to say that something is essential or necessary, for example:

* I must go.

Structure of Must

Must is a modal auxiliary verb. It is followed by a main verb. The structure is:

subject + must + main verb

The main verb is the base verb (infinitive without "to").

Look at these examples:

NOTE:

Use of Must

In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective.

Look at these examples:

* I must stop smoking.
* You must visit us soon.
* He must work harder.

In each of the above cases, the "obligation" is the opinion or idea of the person speaking. In fact, it is not a real obligation. It is not imposed from outside.

NOTE:

We can use must to talk about the present or the future.

Look at these examples:

* I must go now. (present)
* I must call my mother tomorrow. (future)

We cannot use must to talk about the past. We use have to to talk about the past.

# Modal Verbs : Must not, Mustn't (prohibition)