What does must mean?
Must is a modal verb used to express strong necessity, logical certainty, or a firmly held conclusion. It is commonly used in instructions, rules, and warnings: “You must wear a helmet.” It can also indicate that a deduction is virtually certain: “If she completed the marathon, she must have trained extensively.” The related form must have plus a past participle expresses certainty about the past, while mustn't and must not commonly convey prohibition or emphatic denial. Must has no ordinary inflected forms and does not take an -s in the third-person singular. Compared with should, must carries a much stronger sense of obligation, necessity, or certainty; compared with may, it rules out mere possibility. In informal contexts, must can also express an emphatic opinion or recommendation, as in “You must see the film.”
modal verbUsed to express strong obligation or necessity, or to form a strong deduction about what is necessarily true.
- Strong necessity or obligation: something is required.
- Logical deduction: the speaker is certain that something is true because of what is known.
- Past obligation or inference, expressed with must have followed by a past participle.
- An emphatic recommendation or assertion, especially in informal contexts.
"You must submit the application before the deadline if you want to be considered for the position."
"All applicants must provide two references."
"The missing evidence must have been lost in transit."
Must is one of the few English modal verbs that never changes form for third-person singular: he must, never he musts.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of must
The modern English word descends from Old English mōtan, a verb meaning “to have to” or “to need.” Its history is connected with Germanic forms such as German müssen and Dutch moeten, which developed meanings involving necessity and obligation. The modal sense of must became established in Middle English, and the form has remained stable without the usual verb endings.
Related word forms
How must is actually used
Must is a strong modal of necessity and certainty. In the negative, must not expresses prohibition or emphatic denial, while mustn't is common in informal and spoken English. In the past, must have is used for deduction; must be followed by a past participle in this construction.
Easily confused with must
Must expresses strong necessity or logical certainty, whereas should expresses advice, recommendation, or a less demanding expectation.
Must indicates that something is necessary or logically certain, while may indicates possibility or permission.