The evolution of subject-verb agreement in Eastern Tukanoan

This article describes the evolution of past/perfective subject-verb agreement morphology in the Tukanoan family, reconstructing relevant aspects of Proto-Tukanoan verbal morphology and delineating the subsequent diachronic development of verbal subject agreement morphology in the Eastern branch of the family. We argue that suffixes that cumulatively expone past/perfective and person, number, and gender (png) subject agreement resulted from the fusion of post-verbal demonstratives/pronouns expressing png information with suffixes expressing past/perfective tam information. We propose that different png agreement categories developed at successive stages in the diversification of the family, with third person masculine singular subject agreement emerging before other png categories, followed by animate plural agreement, then finally by the development of third person feminine agreement. The result in Eastern Tukanoan was a cross-linguistically unusual agreement system that contrasts four agreement categories: (i) first and second person singular and third person inanimate (singular and plural); (ii) third person animate masculine singular; (iii) third person animate feminine singular; and (iv) third animate plural.