The impersonal passive voice is a verb voice that decreases the valency of an intransitive verb (which has valency one) to zero.[1]
The impersonal passive deletes the subject of an intransitive verb. In place of the verb's subject, the construction instead may include a syntactic placeholder, also called a dummy. This placeholder has neither thematic nor referential content. (A similar example is the word "there" in the English phrase "There are three books.")
In some languages, the deleted argument can be reintroduced as an oblique argument or complement.
In most languages that allow impersonal passives, only unergative verbs may undergo impersonal passivization. Unaccusative verbs may not. The ability to undergo this transformation is a frequently used test to distinguish unergative and unaccusative verbs.[2] In Turkish, for example, the verb çalışmak "to work" is unergative and may therefore be passivized:
The verb ölmek "to die", however, is unaccusative and may not be passivized: