Supervenience (from Latin supervenire, to come upon, to supervene) — A relation of dependence between two sets of properties according to which there can be no difference in the supervenient properties without a difference in the base properties: any two objects, events, or states indistinguishable in all base properties (A) are necessarily indistinguishable in all supervenient properties (B). The notion captures a co-variation without requiring reduction — the supervenient level depends on the base level and cannot vary freely from it, yet it cannot be defined or eliminated in its favour either. The term acquired technical standing in ethics, with R.M. Hare in The Language of Morals (1952), who held that the moral worth of an action cannot differ unless some of its descriptive natural properties differ, and above all in the philosophy of mind, with Donald Davidson in “Mental Events” (1970), who argued that the mental supervenes on the physical without being reducible to it — the thesis of anomalous monism. A clear example: two paintings physically identical brushstroke by brushstroke could not differ in beauty, since aesthetic properties supervene on physical ones. The central distinction opposes supervenience to identity and reduction: to claim that B supervenes on A is weaker than to claim that B reduces to A. Jaegwon Kim, who systematised the concept, distinguished weak, strong, and global supervenience and showed that it is compatible with both physicalism and dualism, leaving the mind-body problem open and giving rise to his celebrated causal exclusion argument.

Origins: Ethics and Philosophy of Mind

The term acquired technical philosophical rigour in two independent contexts that converge in the twentieth century.

In ethics, R.M. Hare used the term “supervenience” in The Language of Morals (1952) to capture a fundamental intuition: moral properties depend on natural properties. If two objects or actions are identical in all their descriptive natural properties (size, shape, consequences, etc.), they must have the same moral value. Hare is credited with introducing the term into moral philosophy by articulating precisely this relation.

In the philosophy of mind, Donald Davidson was the first to use the term technically in “Mental Events” (1970, in Experience and Theory, ed. Foster and Swanson). Davidson argues that mental events are identical to physical events, but that mental predicates are not reducible to physical predicates — a position known as anomalous monism. In this context, he writes that mental properties supervene on physical ones: there can be no mental difference without a physical difference, but mental predicates are not definable in physical terms.

Types of Supervenience

Jaegwon Kim, who systematised the concept from the 1980s onwards (see Supervenience and Mind, 1993), distinguishes at least three forms:

  • Weak supervenience: for every pair of objects in the same possible world, indistinguishability in A implies indistinguishability in B.
  • Strong supervenience: across all possible worlds, indistinguishability in A implies indistinguishability in B.
  • Global supervenience: considers indistinguishability between entire possible worlds, not just between individual objects.

The differences have important metaphysical consequences: strong supervenience is compatible with metaphysical necessity; weak supervenience, only with local co-variation.

Problems and Debates

Kim argued influentially that supervenience, by itself, does not resolve the mind-body problem: it is compatible with both dualism and physicalism. Moreover, Kim proposed the “causal exclusion argument”: if mental events supervene on physical events, and physical events have sufficient physical causes, it seems that mental events are causally idle — which would be problematic for Davidson’s anomalous monism and for any non-reductive physicalism.

In ethics, moral supervenience has been extensively debated: is it a logical, metaphysical, or merely contingent necessity? Its acceptance is compatible with moral non-naturalism (the position of Hare and G.E. Moore, Principia Ethica, 1903) or does it require naturalism?

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