Voice is used to tell whether the subject of the sentence or clause performs the action of the verb or receives the action of the verb. There are two voices in English: active and passive. In the active voice, the subject of the sentence is the agent, or performer of the action, and the object is the receiver of the action. In the passive voice, the grammatical subject of the sentence is the receiver of the action. The agent, if expressed at all, is expressed after the verb in a by-phrase.
Use the passive voice to express actions in which the agent is arbitrary, not known, or not important. Otherwise, use the active voice. To form the passive, use a form of the auxiliary be followed by the past participle of the main verb, and place the receiver of the action in the subject position.
J. Robert Oppenheimer gave the first comprehensive
description of a neutron star in 1939, shortly before he began working on the
first atomic bomb. [The agent, Oppenheimer, is the subject.
The receiver of the action, description, is the object.]
The first comprehensive description of a neutron star was
given by J. Robert Oppenheimer in 1939, shortly before he began working
on the first atomic bomb. [The receiver of the action,
description is the subject. The agent, Oppenheimer, is in
a by-phrase.]
--William J. Kaufmann, "The Black Hole"
In the passive voice, express the agent only if it provides important information for the sentence. If you choose to express the agent, do so in a by-phrase following the verb.
The nickel content of steel was cut by the steel manufacturers during World
War II and never brought back to pre-war levels. Consequently, classic cars made
before the war tend to hold up much longer than later models. [agent,
steel manufacturers, important to the writer's purpose]
The nickel content of steel was cut during World War II
and never brought back to pre-war levels. Consequently, classic cars made before
the war tend to hold up much longer than later models. [agent not
important to the writer's purpose]
--"Take It or Leave It," Valley Comic News
