Chapter II theoretical background of the categories of the verb

1.3 The category of voice
In English as in many other languages, the passive voice is the form of a transitive verb whose grammatical subject serves as the patient, receiving the action of the verb. The passive voice is typically contrasted with the active voice, which is the form of a transitive verb whose subject serves as the agent, performing the action of the verb. The subject of a verb in the passive voice corresponds to the object of the same verb in the active voice. English's passive voice is periphrastic; that is, it does not have a one-word form. Rather, it is formed using a form of the auxiliary verb be together with a verb's past participle.
Canonical passives
Passive constructions have a range of meanings and uses. The canonical use to map a clause with a direct object to a corresponding clause where the direct object has become the subject. For example:
John threw the ball.4
Here, threw is a transitive verb with John as its subject and the ball as its direct object. If we recast the verb in the passive voice (was thrown), then the ball becomes the subject (it is promoted to the subject position) and John disappears:
The ball was thrown.
The original subject can typically be re-inserted using the preposition by:
The ball was thrown by John.
Promotion of other objects
One non-canonical use of English's passive is to promote an object other than a direct object. It is usually possible in English to promote indirect objects as well. For example:
John gave Mary a book. → Mary was given a book.
In the active form, gave is the verb; John is its subject, Mary its indirect object, and a book its direct object; in the passive form, the indirect object has been promoted and the direct object has been left in place. (In this respect, English resembles dechticaetiative languages.)
It is also possible, in some cases, to promote the object of a preposition:
They talked about the problem. → The problem was talked about.
In the passive form here, the preposition is «stranded»; that is, it is not followed by an object. (See Preposition stranding.) Indeed, in some sense it doesn't have an object, since «the problem» is actually the subject of the sentence.
Promotion of content clauses
It is possible to promote a content clause that serves as a direct object. In this case, however, it typically does not change its position in the sentence, and an expletive it takes the normal subject position:
They say that he left. → It is said that he left.