Monism and Statespace Structure*

Theodore Sider is Professor of Philosophy at New York University.

Exotic ontologies are all the rage. Distant from common sense and often science as well, views like mereological essentialism, nihilism, and four-dimensionalism appeal to our desire to avoid arbitrariness, anthropocentrism, and metaphysical conundrums.¹

Such views are defensible only if they are materially adequate, only if they can “reconstruct” the world of common sense and science. (No disrespect to the heroic metaphysicians of antiquity, but this world is not just an illusion.) In the world of common sense and science, bicycles survive changes in their parts, billiard balls strike one another, and nothing travels faster than light. The mereological essentialist denies the first, but offers this replacement: “there exist successions of numerically distinct, but appropriately related, bicycles with different parts” (Chisholm, 1976, chapter 3). The nihilist denies the second, but offers this replacement: “there exist Xs and Ys such that the Xs are arranged billiard-ball-wise, the Ys are also arranged billiard-ball-wise, and the Xs strike the Ys”.² The four-dimensionalist denies the third, but offers this replacement: “no sequences of matter-stages that are related by genidentity travel faster than light”.³ There is room for disagreement over what exactly “reconstruction” amounts to, but at a minimum: when a metaphysical theory reconstructs ordinary sentences φ₁ … as replacement sentences ψ₁ …, ordinary and scientific evidence must not refute the view that, strictly speaking, it is ψ₁ … rather than φ₁ … that are true. The metaphysician needs reconstruction in order to face the tribunal of experience.

An intriguing newcomer to the contemporary scene is the ancient doctrine of monism, the claim that “reality is one”.⁴ I will argue that, contrary to initial appearances, monism can be made materially adequate. But the monist's reconstruction of common sense and science will reveal some troublesome commitments.

1 Existence and Priority Monism

Let's follow Jonathan Schaffer in distingushing two sorts of monism:⁵

• Existence monism Only one object⁶ (concrete particular)exists: the world-object

• Priority monism The world-object may not be the only object, but it is “prior to” all other objects

There are various ways of making sense of “priority”, and of related notions such as metaphysical...