"Shall" and "must" can both imply an obligation, but they are not always interchangeable.
Shall: Traditionally used to express a future action or a formal obligation, especially in legal or contractual contexts. It can indicate a duty, but it often carries a sense of intention or future planning.
Must: Stronger than "shall," it typically conveys a necessity or something that is required without exception. It indicates a stronger imperative, meaning it is something that has to be done.
For example:"You shall report to the manager by 3 PM." (This is a formal obligation, typically used in contracts or rules.)
"You must wear a helmet while riding the bike." (This is a strict requirement or necessity.)
In modern English, "must" is more commonly used for obligations and requirements, whereas "shall" is often seen in formal or legal language.
