A pro-drop language (from "pronoun-dropping") is a language in which certain classes of pronouns may be omitted when they are pragmatically or grammatically inferable. The precise conditions vary from language to language, and can be quite intricate. The phenomenon of "pronoun-dropping" is also commonly referred to as zero or null anaphora. In the case of pro-drop languages, null anaphora refers to the fact that the null position has referential properties, meaning it is not a null dummy pronoun. Pro-drop is only licensed in languages that have a positive setting of the pro-drop parameter, which allows the null element to be identified by its governor. In pro-drop languages with a highly inflected verbal morphology, the expression of the subject pronoun is considered unnecessary because the verbal inflection indicates the person and number of the subject, thus the referent of the null subject can be inferred from the grammatical inflection on the verb.