must

"Must" is a modal auxiliary verb used to express obligation, necessity, or strong recommendation in English. It indicates that something is essential or required, often reflecting rules, laws, or personal judgments. For example, "You must submit your application by Friday" suggests that submitting by that date is a requirement.

In addition to expressing obligation, "must" can convey logical deduction or certainty. For example, "He must be at home" implies a conclusion based on evidence or reasoning. Its usage in this context suggests a high degree of confidence about a situation.

The formality and tone of "must" vary depending on context. It is commonly used in formal communication, instructions, and rules. In everyday conversation, "must" often connotes internal or personal necessity rather than external regulations, such as "I must finish this project."

"Must" differs from other modal verbs like "have to," which also express obligation but can carry nuances of external authority or compulsion. While "must" is often more formal or emphatic, "have to" tends to be more neutral or colloquial.

In negative constructions, "must not" (or "mustn't") indicates prohibition or something that is forbidden. For example, "You must not smoke here" signifies a rule against smoking.

Overall, "must" is a versatile modal verb integral to expressing necessity, certainty, and obligation in English, playing a crucial role in managing both interpersonal expectations and logical deductions.