|Abstract:||Recent advances in Optimality theoretic syntax are characterized by attempts toward a unified approach to linguistic typology and language-internal variation. On the other hand, studies in synchronic (sociolinguistic) variation have long recognized and articulated the obvious link between language variation and historical change. Yet these domains of research continue without much reference to the relation between synchronic typology and diachronic change. This paper attempts to bridge the long-standing gulf between synchronic typology and diachronic (morpho)syntax. The agreement systems in Bantu languages provide an excellent empirical tool for such an attempt, because the historical source of agreement--the notion of `topic salience'--is quite transparent in the synchronic grammars. Furthermore we observe variation in the agreement properties across the Bantu family that suggests a path of diachronic change. I argue that the system of universal, violable constraints in OT enables us to provide a unified approach to synchrony and diachrony by situating the variation in a diachronic context within a single typological space.