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. 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.