Verbs have two voices: an active voice and a passive voice. Voice as the form of a verb shows whether the subject of the verb does the action (the active voice) or whether the action is done to it (the passive voice). Accordingly, we can write a sentence in either of the two different ways. Nearly all the transitive verbs (verbs that have an object) can be used in the passive voice.
The verbs that are never used in the passive voice include elude, escape, flee, get, have, let, like, race, resemble, and suit. Other verbs that cannot be used as passive verbs because they take no direct object which are necessary to become the subjects include arise, consist (of), depend (on), exist, fall, happen, occur, result (from), and rise.
In passive voice, a verb or verb phrase typically uses the verb be (e.g. was), followed by a main verb in the past participle form. The verb is in the active voice when the subject, which can be a person or thing, performs the action. The following examples will show that changing the active sentence into a passive voice causes the subject to become the object, and the object becomes the subject.
His cats ate the fish.
(Subject: cats; verb: ate; object: fish. The doer of the action is the cats. The verb ate is in the active voice and is followed by the object fish.)
The fish was eaten by his cats.
(Subject: fish; verb: eaten; object: cats. This sentence is passive as the action is done to the subject which is the fish. The subject in the active voice cats now becomes the object of the verb eaten.)