What Is Supervenience?

Direct Answer

Supervenience is a formal relation of dependence between two families of properties. In philosophy of mind, the standard thesis is that the mental supervenes on the physical: there cannot be a difference in mental properties — in what someone believes, feels, or experiences — without a difference in physical properties. If two beings are physically identical (their brains, bodies, and environments are exactly the same in all physical respects), then they must be mentally identical as well. No mental change without a physical change; mind is fixed by matter.

The definition captures the core intuition of physicalism while remaining neutral about reduction. A reductive physicalist says mental properties are identical to physical properties. A supervenience physicalist makes a weaker claim: mental properties depend on physical properties, but may remain distinct properties, like a pattern of dots that depends on (but is not identical to) the individual marks. This is why supervenience became the favored way to formulate physicalism: it says the mind is not an independent addition to the physical world, without committing to the strong, and arguably false, claim that mental kinds reduce to neural kinds.

Three distinctions are essential. First, individual vs. global supervenience: individual supervenience says each person's mental state is fixed by that person's physical state; global supervenience says the whole mental character of a world is fixed by its whole physical character. Second, weak vs. strong supervenience: weak supervenience says that within a given possible world, no two things can differ mentally without differing physically (a purely actual, intra-world claim); strong supervenience adds that this holds across all possible worlds — in any world, physical sameness forces mental sameness. Third, supervenience vs. reduction: supervenience is not sufficient for reduction, because it states a pattern of covariation without showing that mental concepts can be analyzed in physical terms. Physicalism is thus typically defined as the supervenience of the mental on the physical, plus the claim that the physical is complete.

Historical Context

The concept of supervenience was introduced into moral philosophy by R. M. Hare in the 1950s (a moral property supervenes on natural properties) and into philosophy of mind by Donald Davidson in 1970, in his paper "Mental Events." Davidson used it to formulate "anomalous monism": all mental events are physical events, but mental properties do not reduce to physical laws; nonetheless, the mental supervenes on the physical, so mental difference requires physical difference. Supervenience let Davidson hold that there is only one kind of stuff while denying psychophysical laws.

The relation was given rigorous formal treatment by Jaegwon Kim, who distinguished its weak, strong, and global versions and argued that supervenience is the right way to formulate the mind-body dependence that any physicalist must accept. Kim later became a leading critic of his own framework, arguing that supervenience without reduction leaves mental properties causally suspect: if the mental is fixed by the physical but not identical to it, it is unclear how mental properties could have any causal powers of their own.

The debate over supervenience also drew on earlier work by W. V. O. Quine and Saul Kripke: Kripke's argument that identity statements are necessary (and that conceivability threatens mind-brain identity) shaped the question of what kind of dependence mental-physical relations could be, and Quine's naturalism framed the demand that mentalistic talk be anchored in the physical.

Key Arguments & Debates

The argument for using supervenience to formulate physicalism is its flexibility and minimalism. It captures the physicalist core commitment — the world is physical, and the mind is not an independent layer of reality — without inheriting the implausible consequences of type identity. A physicalist can accept multiple realizability (the same mental state in many physical systems) and still affirm supervenience, because supervenience concerns the pattern of dependence at the level of individuals and worlds, not the reduction of mental kinds to physical kinds. Moreover, supervenience claims are testable in principle: neuroscience seeks exactly the correlations that would establish physical-to-mental covariance.

The standard objection is that supervenience is too weak to do the work required of it. It states a relation of covariation but gives no explanation of why the mental depends on the physical. As Kim put it, supervenience is not a theory of the mind-body relation; it is a statement of the problem. A magical correlation would satisfy supervenience: if God had decreed that physical states and mental states always covary, supervenience would hold, yet nothing would be explained. A second objection: supervenience allows nonreductive physicalism, but nonreductive physicalism faces the causal exclusion problem — if mental properties are distinct from physical ones and the physical is causally complete, mental properties threaten to be epiphenomenal (real but causally inert). A third set of problems concerns the formulation itself: weak supervenience is too weak to express genuine dependence (it holds in any world with fixed actual correlations), while global supervenience is hard to state precisely and may be compatible with all sorts of nonphysicalist scenarios.

Defenders respond that supervenience is not meant to explain dependence but to locate the mind-body relation precisely, and that the demand for explanation is satisfied by the rest of physicalist theory. Others argue that physicalism should be defined more modestly, in terms of the physical facts fixing the mental facts — a formulation that is, in effect, supervenience.

Contemporary Relevance

Supervenience remains the standard formal vocabulary of philosophy of mind. It structures debates about the neural correlates of consciousness: to say that consciousness supervenes on the brain is to say that the complete physical state of the brain fixes the state of consciousness. The concept also travels beyond the mental: supervenience is used in ethics (moral supervenience on the natural), aesthetics, and the philosophy of science to state all manner of dependence claims.

In the AI debate, the question of whether machine consciousness is possible can be framed as a supervenience question: if consciousness supervenes on functional organization alone, then a functionally identical machine must be conscious; if it supervenes on biological properties, it need not be. And the debate between reductionists and emergentists about consciousness often reduces, formally, to a dispute about what kind of supervenience holds and whether supervenience plus distinctness (as in emergentism) is coherent — which is why the concept remains indispensable.

Related Concepts

• The identity theory: the reductive thesis supervenience was designed to soften.
• Emergentism: the view that mental properties supervene on but are irreducible to physical ones.
• Multiple realizability: the phenomenon that motivates nonreductive physicalism.
• The explanatory gap: the puzzle about why mental-physical dependence holds.
• The hard problem vs easy problems: the question of what, if anything, supervenience leaves unexplained.

Further Learning

• Stanford Encyclopedia of Philosophy: Supervenience
• Internet Encyclopedia of Philosophy: Supervenience
• Donald Davidson, "Mental Events," in Experience and Theory, ed. Foster and Swanson (1970).
• Jaegwon Kim, Supervenience and Mind (Cambridge University Press, 1993).