must for subjective obligation

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

Structure of must

Must is a modal auxiliary verb. It is followed by a main verb.

The basic structure for must is:

subject + auxiliary verb
must
+ main verb
base

The main verb is always the same form: base

Look at these examples:

subject auxiliary verb
must
main verb
base
I must go home.
You must visit us.
We must stop now.
Like all auxiliary verbs, must cannot be followed by to. So, we say:
  • I must go now.
    not I must to go now.

Use of must

In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective. Look at these examples:

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.

It is sometimes possible to use must for real obligation, for example a rule or a law. But generally we use have to for this.

We can use must to talk about the present or the future. Look at these examples:

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