Abstract

_Grounding_ is meant to be a metaphysically explanatory relation of non-causal constitutive determination. Recently there has been significant interest in the idea that there might be ‘laws of metaphysics’ for grounding, analogous to the laws of nature for causation. In this paper I argue that current accounts of the structure of law-based grounding (focusing on Jonathan Schaffer’s structural equation modeling account) do not capture grounding’s directionality—a central feature. The formal account must be supplemented to satisfy this demand and give a successful general account of directed grounding relations. I thus propose two alternative supplements: Priority-Inextricable Grounding and Priority-Extricable Grounding (itself divided into two alternatives—Priority by Absolute Fundamentality and Priority by Relative Fundamentality). Each supplement offers a distinct image of grounding—most illustratively, modally: for each, the structure of grounding contrastingly constrains the metaphysical compossibility of worlds that share facts or grounding relations. As such, I conclude that the supplements offer incompatible strategies for sourcing grounding directionality and grounding theorists ought to decide between them.