<P> 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 that the null position does have 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 . </P>
why can you leave out the subject pronoun in spanish
null anaphora refers to the fact that that the null position does have referential properties , meaning it is not a null dummy pronoun