Passive constructions are those in which the acted-on noun, rather than the word(s) denoting the actor, is the subject of the sentence, as in the last sentence of the lead paragraph of this post. The well-founded prejudices against the passive include that such constructions are usually less concise than those organized in the active voice, that they obscure the identity of the actor, and that they upend traditional English syntax.
But the passive voice is suitable in the following cases:
1. When the emphasis is on the acted-on, not the actor: “The message was conveyed by the courier.”
2. When the actor is not pertinent or is implied: “The defendant was found not guilty.”
3. When the actor cannot be identified: “The dog was poisoned.”