Is “must be” passive voice?
"Must be" + a past participle is a modal passive: "Receipts must be kept for seven years." "Must be" + an adjective or noun is active: "You must be joking." Requirement language leans on this passive because the rule applies to everyone.
Regulations, policies and safety notices are full of “must be” passives: “Guards must be installed on all moving parts.” The reader is the implied doer, and plain-language guides generally prefer to say so: “You must install guards on all moving parts.”
Keep the passive when the obligation really does fall on an unnamed party, or when the sentence is about the object, not the actor.
Three sentences, checked
Each example below was run through our engine (v1.0.0). Amber marks the passive construction; a dotted underline marks a “be + participle” that is an adjective, not a passive.
Related forms
- Is “was” passive?
- Is “is” passive?
- Is “has been” passive?
- Is “have been” passive?
- Is “had been” passive?
- Is “will be” passive?
- Is “can be” passive?
- Is “could be” passive?
See the full list of passive voice verbs and passive voice in all twelve tenses.
Questions people ask
- Does plain-language guidance ban "must be" passives?
- No. Guidance such as plainlanguage.gov prefers active voice and says who is responsible, but it treats passive as a choice to justify, not a banned form.