In grammar, voice is the relationship between the action or state expressed by a verb, and its arguments (subject, object, etc.). When the subject is the agent or actor of the verb, the verb is said to be in the active voice. When the subject is the patient, target or undergoer of the action, it is said to be in the passive voice.
For example,
The cat ate the mouse
is active, but
The mouse was eaten by the cat
is passive.
In a transformation from an active voice sentence to an equivalent passive voice construction, the subject and the direct object switch places. The direct object is promoted to subject, and the subject is demoted to an optional complement. In the above examples, the mouse is the direct object in the active voice version, the subject in the passive version. The subject of the active voice version, the cat, becomes part of a prepositional phrase in the passive version of the sentence, and could be left out entirely. In the English language, the passive voice is periphrastic; that is, it is not a single word form, but rather a construction making use of other word forms. Specifically, it is made up of a form of the auxiliary verb to be and a past participle of the main verb. In other languages, such as Latin, the passive voice is simply marked on the verb by inflection: the passive voice uses different verb endings than the active voice
