The document discusses the active and passive voice. In the active voice, the subject of the sentence performs the action. In the passive voice, the subject receives the action. The passive is formed by using some form of "to be" plus the past participle of the main verb. The passive voice is generally more formal and is used when the performer of the action is unknown or unimportant. Leaving out the agent in a passive construction can be more dramatic or avoid implicating who performed the action.