1 Categorical priority and categorical collapse.1

A central project of contemporary metaphysics is to understand the nature of the world as a whole. The traditional way to approach this project is to develop an account of the metaphysically basic kinds, that is, of the fundamental ontological categories of the world. But in addition to giving an account of what the fundamental ontological categories are, we need to give an account of how they and their members ground the overall structure of the world. This means that a fully developed fundamental ontology has a complex, interlocking structure. Part of the structure is determined by the nature and organization of the fundamental and derivative ontological categories, and part of the structure is determined by the way members of the categories are arranged and related in the world. Thus, an account of the metaphysical ground of reality has three central elements: (i) an account of what the metaphysically basic categories and the relations between them are, (ii) an account of the way members of these basic categories are combined and arranged, and (iii) an account of the rules of ground, that is, an account of how the metaphysically basic categories, their members, and their arrangements ground the rest of reality. I will discuss the project of understanding the nature of the world as a whole primarily in terms of the way metaphysically basic categories and the members of these categories are arranged so as to provide the ground for all of reality. Once we have the metaphysically prior ground, we have, as it were, the ontological initial conditions from which the rest of reality, the metaphysically derivative remainder, is generated. The fundamental ontological categories are the most basic kinds or natures of the world. (i)-(iii) give us two different sorts of fundamental ontological structure. The fundamental categorical structure of the world is given by the number and kinds of fundamental ontologica