I've been taught that the word "shall" represent obligatory or mandatory. On the other hand, I was taught by another lecturer that "must" represent mandatory.

Which one of the two represents obligatory? When I asked a teacher this question, he told me "shall" is also synonymous to might or maybe. Is this true?

As an example, consider:

  • He shall report the case to his senior officer.
  • He must report the case to his senior officer.
  • 2
    The meaning of shall to a large extent depends on tone (as well as context). In the first example, if it is expressed with emphasis on shall, it is more or less a command; if there is no emphasis on shall, then it is more of a predictor (or at any rate, less commanding). There are also differences in uses between NAE and BrE (the use of shall is more common in the latter). Commented Nov 17, 2016 at 15:49
  • 1
    Must is closer to being uniformly obligatory. Commented Nov 17, 2016 at 15:49
  • I've noticed that some people whose first language is not English use shall when then really mean should. Dunno why, or how this habit developed. A guess is that their first language might be German (?).
    – Drew
    Commented Nov 17, 2016 at 18:42
  • We say represents something mandatory or obligatory. Those are adjectives.
    – Lambie
    Commented Oct 4, 2021 at 12:33

2 Answers 2


"Shall" is not synonymous with "might" or "maybe." It is synonymous with "will."

"Must" carries the semantics of mandatory action more than "shall."

In Australian and UK varieties of English (I can't speak for American) "shall" is on the way out, being replaced by "will." I think originally the semantic difference between the two words was that "shall" simply indicated that the action would take place in the future, and "will" had more of a personal intention element, but that distinction has disappeared.

  • Simple and to the point. Except bear in mind: Shall I open the window? Still very much used.
    – Lambie
    Commented Oct 4, 2021 at 12:31
  • @Lambie In your example, "Should I" would commonly replace "Shall I."
    – Steve
    Commented Oct 4, 2021 at 16:29
  • Not necessarily. Should I close the window sounds close to an obligation. Shall is use for suggestions in English. Should is not. Shall I/we = suggestions or to offer something. Shall we leave?
    – Lambie
    Commented Oct 4, 2021 at 20:16

Nobody uses "shall" in common speech. It's one more example of unnecessary lawyer talk. Nobody says, "You shall finish the project in a week."

For all these reasons, "must" is a better choice

In general, must is used if the sentence’s subject is an inanimate object, in other words, where the subject is not a person or a body on which a duty can be imposed.

  • Parent to child: You shall do your homework now.
    – Lambie
    Commented Oct 4, 2021 at 12:30
  • Engineering requirement documents use shall all the time.
    – jimm101
    Commented Oct 4, 2021 at 15:47
  • @jimm101: I agree — except that your point should be developed into an answer, or, if not that, posted as a comment on the question. Commented Oct 5, 2021 at 4:26
  • @Scott I was commenting on the answer's assertion that shall is an "example of unnecessary lawyer talk". My comment doesn't answer or address the question.
    – jimm101
    Commented Oct 5, 2021 at 11:28

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