When working out the structure of the world, and what depends on what, one of the important questions to address is how entities traditionally assigned to different categories relate to each other. What, for example, is the relation between things and events? Or events and instances of properties? Or any of these and states of affairs? Are any of these ontologically dependent on any of the others? Can we spell out this 'ontological dependence' in any more specific or clearer way?
Connected with this question is a question about the categories themselves. Consider the category of properties itself (as opposed to just the properties that fall within it). Does it ontologically depend on anything else? Are there dependence relations between the categories themselves, as opposed to the members of the different categories? And if there are relations of dependence between categories themselves, or between categories and various noncategories, can we spell out this dependence in any more specific or clear way to illuminate it?
In this paper I want to do two connected things. The first is to explore, in general terms, some of the issues that come up when we start considering ontological categories and questions about relations of dependence between them (either between the members of one and the members of another, or between the categories themselves). The second is to discuss one particular way we could try to illuminate the apparent dependence relationships between categories (or apparent categories): by exploring and tentatively defending a particular account of how ordinary things are related to events, and how we might relate the putative category of 'physical object' (or 'thing', as I will call them) to the putative category of 'event'.