Most style advice boils down to "use active voice." That's a decent default, but it skips the more useful skill: recognizing passive voice when you write it, and knowing the handful of situations where it's actually the right call. Here's the short version, without the grammar-class jargon.

The actual difference

In an active sentence, the subject performs the action: the editor cut the paragraph. In a passive sentence, the subject receives the action instead: the paragraph was cut by the editor, or even the paragraph was cut, with no actor named at all. The passive version isn't grammatically wrong — it's just a different way of arranging the same information, and it usually takes more words to do it.

The fastest way to spot it

Look for a form of "to be" (is, was, were, been, being) followed by a past-tense verb — "was written," "were chosen," "is being reviewed." If you can insert "by zombies" after the verb and the sentence still makes grammatical sense ("the report was reviewed by zombies"), it's passive. Active sentences fail that test, because the subject is already doing the acting.

Why it usually reads weaker

Passive voice adds words without adding information — "was reviewed by" is three words doing the work "reviewed" could do alone. It can also hide who's responsible for an action, which is fine in some contexts and a real problem in others. "Mistakes were made" is passive voice doing exactly what critics accuse it of: removing the actor from the sentence entirely.

When passive voice is the right choice

Passive voice earns its place in a few specific situations, and good writers use it on purpose in each one:

• The actor is unknown or irrelevant. "The window was broken sometime last night" — you may not know who did it, and the sentence doesn't need to guess.
• The result matters more than who caused it. "The bridge was completed in 1937" puts the focus where a reader wants it — on the bridge, not the construction crew.
• Scientific and technical writing. "The sample was heated to 80°C" keeps the focus on the process rather than the researcher performing it — a long-standing convention in lab reports for good reason.
• Softening a criticism deliberately. "The deadline was missed" reads less accusatory than "you missed the deadline" — useful in some professional contexts, though it can also read as evasive, so use it knowingly.

Quick check before you submit

Scan for "was," "were," and "been" — not to eliminate every instance, but to ask, for each one, whether the sentence would be clearer and shorter with the actor moved to the front. Most of the time it will be. Occasionally, as above, the passive version is doing exactly what you need it to do.