When doing metaphysics, it is frequently convenient and sometimes essential to rely upon various concepts of fundamentality when articulating the problems, positions, and arguments at issue. But what it is, exactly, that these concepts are supposed to track remains obscure. The goal of this dissertation is to develop and defend a theory about the metaphysics of fundamentality. By doing so, I clarify and vindicate the roles that concepts of fundamentality play in metaphysics. At the theory’s core are two other concepts frequently relied upon in metaphysical inquiry: of something’s being ‘derived from or 'ultimately in virtue of’ something else (the concept of grounding), and of something’s ‘reducing to’ or ‘really just consisting in’ something else (the concept of reductive analysis).
I begin by arguing that concepts of grounding ought to serve as a foundation for understanding the metaphysics of fundamentality more generally (Chapter 2, “Grounding the Metaphysics of Fundamentality”), and then propose an account of reductive analysis that retains the traditional insight that a reductive analysis purports to describe the constituents of a property or fact and depict how they are structured together (Chapter 3, “On What Consists in What”). I then argue that even though grounding neither entails nor is entailed by reduction, facts about grounding can be understood wholly and without circularity in terms of facts about reductive analysis (Chapter 4, “Getting Grounded”). Finally, I conclude by challenging the widespread assumption in literature on the metaphysics of fundamentality, and in first-order disputes about what grounds what, that a fact is metaphysically necessitated by the facts that ground it (Chapter 5, “Against Grounding Necessitarianism”).