Schaffer offers us in the last section of “On What Grounds What” (2009) an applied illustration of his allegedly Aristotelian metaontological position. According to this illustration, Schaffer’s metaontological position, supplemented with a few Aristotelian theses about substance and grounding, would converge in a view remarkably similar to his priority monism (Philosophical Studies, 145, 131–148, 2009b; Philosophical Review, 119, 31–76, 2010a), the view that there is one single fundamental substance. In this paper, I will argue against Schaffer’s suggestion that priority monism (...) represents a viable development of Aristotelian metaphysics. In particular, I will hold that the most plausible version of Schaffer’s priority monism by Aristotelian standards fails to satisfy basic Aristotelian tenets about dependence, composition, change, and persistence, and suggest that this is evidence that Aristotelians are more at home with a pluralism rather than a monism about substance. (shrink)