Passive voice occurs when the object of a verb appears as the subject of a sentence. In passive constructions, the agent — or ‘doer’ — of a given action does not appear until later in the sentence, if it appears in the sentence at all. Most often, passive constructions consist of a derivative of ‘to be’ plus the past participle of a transitive verb. Consider the following sentence: ‘The cheese was eaten by the mouse.’ The subject, ‘cheese,’ does not perform any action, and the sentence could stand alone without the prepositional phrase that contains the agent, ‘the mouse.’ The active counterpart to this sentence, ‘The mouse ate the cheese,’ places the agent in the position of subject, and tells you who or what performs the action in the sentence.
Passive voice is not grammatically incorrect, and there are many situations in which you might use this construction. Many scientific writing situations require passive construction, from lab reports or journal articles, to establish objectivity — that is, to remove yourself from the experiment or research about which you are writing. Passive voice is also useful when you want to emphasize the object or de-emphasize or omit the subject for dramatic effect. For instance, you might write ‘The cheese was stolen’ if you do not know who performed the action.
ACTIVE VOICE: We found that 90 percent of our subjects recoiled in horror when we served them cheese topped with a live mouse.
PASSIVE VOICE: All conventions and standards were observed in this experiment, and no mice were harmed.
Many instructors and style guides prohibit the use of passive voice, and some restrict derivatives of ‘to be’ altogether in order to discourage you from writing passively. In general, using the active voice instead of passive constructions lends clarity, concision and directness to your writing. Active verbs result in more engaging, vivid prose, and in academic and other kinds of writing, active voice provides an air of authority to your declarations.
PASSIVE VOICE: The wedge of cheese was contaminated by mice when the refrigerator door was left ajar.
ACTIVE VOICE: Herds of mice swarmed the streets when the cheese truck emptied its contents after the crash.