Null subjects, switch-reference, and serialization in Jabem and Numbami

Analysis of null vs. overt subject NPs over successive clauses in texts fro m Numbami and Jabem, two Austronesian languages of Papua New Guinea with ri ch subject-agreement morphology and rich verb serialization, reveals that o ptional null subjects normally signal subject retention across clauses whil e optional overt subjects signal switches. Comparison of these discourse-le vel switch-reference systems with clause-level verb serialization in the sa me languages, and with morphological switch-reference systems in neighborin g Papuan languages and distant Austronesian languages reveals considerable functional overlap between canonical switch-reference systems and canonical verb-serialization systems, but with null subject NPs signaling similar ty pes of continuity in both systems. Optional null subjecthood marks not just subject continuity across successive clauses at the discourse level, but a lso actor continuity, just as obligatory null subjecthood on noninitial ver bs marks continuity of actors, patients, and other thematic roles across su ccessive serialized verbs at the clause level.