Use of Must in English

Use of Must in English

"Must" is most commonly used to express certainty. It can also be used to express necessity or strong recommendation, although native speakers prefer the more flexible form "have to." "Must not" can be used to prohibit actions, but this sounds very severe; speakers prefer to use softer modal verbs such as "should not" or "ought not" to dissuade rather than prohibit.
In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective. Look at these examples:

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

Examples:

• This must be the right address! certainty
• Students must pass an entrance examination to study at this school. necessity
• You must take some medicine for that cough. strong recommendation
• Jenny, you must not play in the street! prohibition

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

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