Shall vs. must

One of the frequently asked questions is when to use shall and when to use must. Shall is a formal term used primarily in contracts,…


Hi this is Peter and welcome to TransLegal's lesson of the week.

Today we're going to be talking about the difference between shall and must.

This is quite a common question that we get here at TransLegal and so I'll just start by saying that really there's no hard, fast rule with respect to the use of modal verbs like shall, will, must, may, etc. They can be used pretty much interchangeably.

For example, shall and must are virtually identical in meaning, however shall is usually deemed to be the more formal of the two and is used only in contracts, legislation or similar documents.

Now the definitions up here may be useful. You can see here shall means has a duty to, must is required to, may has discretion or permission to and will expresses a future contingency. As seen here, shall is used when a person or entity has a duty to perform a certain act.

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.

In practice though there is little distinction between shall and must and thus no reason to really worry about the use of either. But note, if you elect to use shall as a mandatory term make sure that must would work as well.

That's it for today. If you have any questions about shall and must or modal verbs, please leave a question for us in the comments section below and myself or one of my colleagues will get back to you. Thanks.