Alex McQuibban
University of St Andrews & University of Stirling
This paper interrogates the metaphysical foundations of David Lewis’ system, arguing that the contingency of both Humean Supervenience (HS) and the nature of properties on which the facts of our actual world supervene undermine the applicability and very foundations of his wider metaphysical project. For Lewis, HS is a contingent hypothesis about the actual world: that all facts supervene on the spatiotemporal arrangement of perfectly natural properties and their relations. Yet the contingency of HS becomes fatal once we acknowledge the metaphysical possibility of non-Humean worlds structured such that higher-level facts do not supervene on their spatiotemporal mosaics and worlds which otherwise include wholly alien properties. If such worlds are possible (as Lewis himself granted), and if some could be empirically indistinguishable from ours, then it seems we cannot know whether we inhabit a genuinely Humean world or one that merely appears so. The upshot is a kind of metaphysical structural scepticism: even if Lewis’ analyses are internally coherent, they are only suitable for making sense of ‘normal’ Humean worlds, rendering their applicability to our own world epistemically fragile as Lewis’ modal analyses of metaphysical concepts (causation, laws, etc.) rely on notions like similarity and Best System Analysis, which may be disrupted by alien properties and in non-HS worlds. Given our empirical access precludes certainty about the deep metaphysical structure of reality, the epistemic possibility of such scenarios remains live. It also suggests that such non-compliant worlds might at least be closer in modal space to our own than Lewis expected. Either prospect – epistemic or modal – is enough to upend Lewis’ entire metaphysical system. This paper exposes and substantiates these worries, and considers responses (e.g., recasting HS as necessary and relaxing Lewis’ ontological commitments) and implications (e.g., concerns implied for all ambitious modal theories).
Chair: Peihong Xie
Time: 05 September, 11:20-11:50
Location: HS E.002
SOPhiA 2026 