understood as implicit anaphoric direct objects, that is, those whose referents can be understood from the prior or ongoing discourse context as well as sufficiently salient in that context not only to be encoded pronominally, but even to be entirely omitted. However, it is not imperative that the referent of the direct object has been referred to explicitly previously in the discourse; it could instead be accessible extra-linguistically due to its salience to the interlocutors. Defective verb An impersonal verb is different from a defective verb in that, with an impersonal verb, only one possible syntactical subject is meaningful (either expressed or not), whereas with a defective verb, certain choices of subject might not be grammatically possible, because the verb does not have a complete conjugation. In universal grammar theory Impersonal verbs can be considered null subject data. They involve a general concern in generative grammar: determining the nature and distribution of phonetically null but syntactically present entities (empty categories). Since, by definition, these entities are absent from the speech signal, it is of interest that language learners still can come to have information about them. As this phenomenon could not have resulted from sufficient prior experience, it suggests the role of universal grammar. See also Gender-specific and gender-neutral third-person pronouns Generic you Impersonal passive voice Impersonal pronoun "one" Null-subject language Transitive verb Transitivity (grammar) References Transitivity and valency