Chinese prominently allows its subjects and objects (arguments) or parts of arguments to be omitted (labeled as nominal ellipsis). This partially contributes to the widespread perception that Chinese is a discourse-oriented or topic-prominent language and that discourse/context or pragmatics are responsible for leaving elements unsaid and for interpreting them; what will be understood from context can be omitted. This article emphasizes the fact that, even though context can be a factor, the acceptability of nominal ellipsis and the different interpretive possibilities for null subjects and null objects must follow grammatical constraints. Such restrictions are not predicted or accommodated by approaches that analyze null subjects and null objects in the same way or by a deletion mechanism applying to the Phonological Form (PF-deletion). Available proposals that treat null subjects and null objects differently are evaluated and it will be shown that null subjects and null objects can be distinguished without stipulations. A null subject can be an empty pronoun but not a null object. A null object is a placeholder that is empty in content. Such an empty element is also responsible for the fact that noun phrases restrict their subparts that can be missing. Missing contents are filled via copying of lexical materials at the Logical Form (LF-copying).