PASSIVE VOICE

Passive voice is a grammatical voice common in many of the world's languages. In a clause with passive voice, the grammatical subject expresses the theme or patient of the main verb  that is, the person or thing that undergoes the action or has its state changed. This contrasts with active voice, in which the subject has the agent role. For example, in the passive sentence "The tree was pulled down", the subject (the tree) denotes the patient rather than the agent of the action. In contrast, the sentences "Someone pulled down the tree" and "The tree is down" are active sentences.

Typically, in passive clauses, what would otherwise be expressed by the object (or sometimes another argument) of the verb comes to be expressed by the subject, while what would otherwise be expressed by the subject is either not expressed at all, or is indicated by some adjunct of the clause. Thus transforming an active verb into a passive verb is a valence-decreasing process ("detransitivizing process"), because it transforms transitive verbs into intransitive verbs.

Many languages have both an active and a passive voice; this allows for greater flexibility in sentence construction, as either the semantic agent or patient may take the syntactic role of subject. The use of passive voice allows speakers to organize stretches of discourse by placing figures other than the agent in subject position. This may be done to foreground the patient, recipient, or other thematic role it may also be useful when the semantic patient is the topic of on-going discussion. The passive voice may also be used to avoid specifying the agent of an action.

The passive voice in English

English, like some other languages, uses a periphrastic passive. Rather than conjugating directly for voice, English uses the past participle form of the verb plus an auxiliary verb, either be or get, to indicate passive voice.

The money was donated to the school.

The vase got broken during the fight.

All men are created equal.

If the agent is mentioned, it usually appears in a prepositional phrase introduced by the preposition by.

Without agent: The paper was marked.

With agent: The paper was marked by Mr. Tan.

The subject of the passive voice usually corresponds to the direct object of the corresponding active voice (as in the above examples), but English also allows passive constructions in which the subject corresponds to an indirect object or preposition complement:

We were given tickets. (subject we corresponds to the indirect object of give)

Tim was operated on yesterday. (subject Tim corresponds to the complement of the preposition on)

In sentences of the second type, a stranded preposition is left. This is called the prepositional passive or pseudo-passive (although the latter term can also be used with other meanings).

The active voice is the dominant voice in English at large. Many commentators, notably George Orwell in his essay "Politics and the English Language" and Strunk & White in The Elements of Style, have urged minimizing use of the passive voice. However, the passive voice has important uses. Jan Freeman of The Boston Globe states "all good writers use the passive voice" including Orwell and Strunk & White themselves, in the sections of their essays criticizing the passive voice. There is general agreement that the passive voice is useful for emphasis, or when the receiver of the action is more important than the actor.

Referensi:
https://en.wikipedia.org/wiki/Passive_voice