Referential arguments of a verb may be realized as zero pronouns. This is especially common for subjects. Null anaphora is constrained by both syntax (shared arguments are expressed only once) and discourse structure (null elements must be easily accessible in the context).
The term ‘null anaphora’ refers to cases where an argument position of a predicate is filled not by an overtly realized element, but by an invisible anaphoric pronoun (Anaphoric Processes). The n…