"Must" can be:
* A modal verb: When used to express obligation, necessity, or strong probability, "must" acts as a modal verb. It doesn't have a tense of its own and always appears before another verb.
* Example: You must study hard for the exam.
* An adjective: In some contexts, "must" can function as an adjective, meaning "absolutely necessary" or "essential".
* Example: This is a must-have item for any traveler.
Therefore, it's important to look at the sentence structure to determine whether "must" is acting as a verb or an adjective.