In this dissertation, I investigate factors underlying the distribution of object case in Kwak´wala, an endangered Northern Wakashan language of British Columbia, Canada. Kwak´ wala has two types of objects, instrumental (=s) and accusative (=xˇ). To account for their distribution, I develop a semantic theory of object case that is grounded in event structure. The first central claim of this theory is that instrumental case marks internal arguments which participate in initiating subevents ( Co-initiators), while accusative case marks internal arguments which participate in non-initiating subevents (Non-initiators ). Concomitantly, any internal argument which participates in both the initiating and non-initiating subevents of an event can undergo instrumental/accusative case alternation. The second central claim of this theory is that instrumental case adds semantic value, while accusative case is a meaningless default.

Supporting evidence for these claims comes from field data. On the one hand, object case realization is constrained by verb meaning, as shown by the existence of correlations between particular semantic verb classes and particular case frames. On the other hand, evidence that case realization is determined by event structure comes from data showing that modifying event structure affects case realization. Three types of event structure modification which license case alternation include the Direct Manipulation Alternation, the Caused Motion Alternation, and semantic incorporation with the affixal verb -(g)ila 'make'. The event-structural basis of object case is also revealed in the vicinity of weak verbs (Ritter & Rosen 1996) where the semantic value of object case is communicated independently of lexical entailments.

This analysis allows us to see how Kwak´ wala's object case system manifests a wider cross-linguistic tendency for languages to grammaticalize a link between object-encoding and event structure. I illustrate this by showing that Kwak´wala's object case system is semantically the mirror image of the object case system in Finnish, in which the final bound of events is grammaticalized as an interpretable accusative case (Leino 1982, Heinämäki 1984, 1994, Kratzer 2004). Taking an even wider view, Kwak´ wala fits squarely within the event-structural typology proposed in Ritter & Rosen (2000), where languages are divided according to whether they grammaticalize the initial or final bound of events. Kwak´wala's object case system thereby fits into existing cross-linguistic patterns while also expanding our notions of what a possible case system looks like.