must for subjective obligation
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 basic structure for must is:
The main verb is always the same form: base
Look at these examples:
- I must go now.
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:
- 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.
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.