Voice (grammar)

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In grammar, the voice (aka diathesis) of a verb describes the relationship between the action (or state) that the verb expresses and the participants identified by its arguments (subject, object, etc.).^[1] When the subject is the agent or doer of the action, the verb is in the active voice. When the subject is the patient, target or undergoer of the action, the verb is said to be in the passive voice.^[2][3][4] When the subject both performs and receives the action expressed by the verb, the verb is in the middle voice.

The following pair of examples illustrates the contrast between active and passive voice in English. In sentence (1), the verb form ate is in the active voice, but in sentence (2), the verb form was eaten is in the passive voice. Independent of voice, the cat is the Agent (the doer) of the action of eating in both sentences.

1. The cat ate the mouse.
2. The mouse was eaten by the cat.

In a transformation from an active-voice clause to an equivalent passive-voice construction, the subject and the direct object switch grammatical roles. The direct object gets promoted to subject, and the subject demoted to an (optional) adjunct. In the first example above, the mouse serves as the direct object in the active-voice version, but becomes 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 can be left out entirely; The mouse was eaten.