A sentence gets marked as "passive voice" by a grammar checker, and the instinctive reaction is often to rewrite it immediately, because passive voice has such a strong reputation as something to eliminate on sight. That reputation is somewhat overstated — passive voice is a legitimate grammatical construction with genuine uses, and understanding what it actually does structurally makes it much easier to judge when a flagged sentence genuinely needs revising and when the passive construction is actually the better choice.
What passive voice actually changes, structurally
In an active-voice sentence, the grammatical subject performs the action: "the committee approved the proposal." In a passive-voice sentence, the grammatical subject receives the action instead, and the entity performing the action either moves to a prepositional phrase or gets omitted entirely: "the proposal was approved by the committee," or simply "the proposal was approved." That's the entire structural distinction — which noun phrase occupies the subject position, and whether the actor doing the action is still explicitly named at all.
Why passive voice earned its bad reputation
The common critique of passive voice centers on two real issues. First, passive constructions are frequently a few words longer than their active equivalent, since the sentence needs an extra helping verb and often a prepositional phrase to reintroduce the actor. Second, and more substantively, passive voice allows the actor performing an action to be omitted entirely without the sentence becoming grammatically incomplete — "mistakes were made" is a complete, grammatically valid sentence that conspicuously avoids naming who actually made the mistakes. This omission capability is exactly why passive voice has a reputation for being used, sometimes deliberately, to obscure accountability in corporate and political communication, where naming a specific actor might be inconvenient.
Where passive voice is genuinely the better choice
Despite its reputation, there are several situations where passive voice is the clearer, more appropriate, or simply more natural construction, and rewriting into active voice would actually make the sentence worse rather than better. When the actor performing an action is genuinely unknown, irrelevant to the point being made, or already established clearly by context, passive voice lets you focus attention on the more important element — the thing being acted upon — without cluttering the sentence with a less important or already-obvious actor. "The bridge was completed in 1937" is a perfectly natural, clear sentence; forcing it into active voice ("Workers completed the bridge in 1937") introduces an actor (workers) that wasn't the actual point of the sentence and doesn't meaningfully improve clarity.
Scientific and technical writing has also traditionally favored passive voice specifically because it shifts emphasis away from who performed an experimental procedure and onto the procedure and its results themselves, which is often the genuinely more relevant information in that specific context — though even within scientific writing, style conventions have shifted somewhat toward favoring active voice more often than in previous decades.
Why grammar checkers flag passive voice as a blanket suggestion rather than a rule
Because passive voice is a legitimate, sometimes genuinely preferable construction rather than a grammatical error, most well-designed grammar and style checkers flag it as a stylistic suggestion to review rather than an outright mistake requiring correction — the tool is specifically pointing out "here's a passive construction, consider whether active voice would communicate more clearly and directly in this particular case," not asserting that every single instance is objectively wrong and must be changed. Treating every flagged instance as an automatic, non-negotiable fix, without actually evaluating whether the passive construction was the right choice for that specific sentence, tends to produce writing that's mechanically "active voice everywhere" without necessarily being clearer or more effective as a result.
A practical test for evaluating a flagged sentence
A genuinely useful practical question to ask about any passive-voice sentence a checker flags: does the sentence become clearer, more direct, and more informative if rewritten in active voice, specifically because naming the actor adds real value the reader needs? If yes, revise it. If the actor is genuinely unknown, unimportant to the point being made, or would just add unnecessary clutter without improving clarity, the passive construction was likely the right call in the first place, and the flag can reasonably be dismissed rather than mechanically "fixed."
Reviewing your own writing
Our writing style checker highlights passive voice constructions alongside other stylistic patterns like overly long sentences and adverb-heavy phrasing, giving you the chance to evaluate each flagged instance individually against the practical test above, rather than mechanically converting every single flagged sentence to active voice regardless of whether that actually serves the specific sentence better.