Kim’s Supervenience

Philosopher Jaegwon Kim’s supervenience theory of consciousness seeks to reconcile mental causation with a physicalist ontology. Supervenience is a way of thinking that defines how mental states relate to physical states, especially in the context of reductionism and the causal closure of the physical domain (Kim, 2010).

According to Kim, “mental properties supervene on physical properties” means that “No mental difference without a physical difference.” Or more formally, “The mental supervenes on the physical in that things (objects, events, organisms, persons, and so on) that are exactly alike in all physical properties cannot differ with respect to mental properties. That is, physical indiscernibility entails psychological indiscernibility.”

In other words, mental properties supervene on physical properties if any two entities that are identical in all their physical properties will also be identical in all their mental properties, and there cannot be a difference in mental properties without a difference in physical properties.

Kim stresses that “this principle does not say that things that are alike in psychological respects must be alike in physical respects... the same psychology could be realized in different physical systems… mind-body supervenience asserts only that creatures could not be psychologically different and yet physically identical.” Thus, the same mental state can be realized by different physical states, which is consistent with functionalism and multiple realizability (Kim, 2010).

Critically, supervenience itself is not an explanation for how the physical generates the mental; it does not even try to explain how mental states arise from physical states. It's a dependency relationship, not a causative mechanism.

The Causal Exclusion Problem

Kim defends a causal exclusion problem as follows. Every physical event that has a cause has a sufficient physical cause (based on the causal closure of the physical). If a mental event causes a physical event, and it is not reducible to a physical event, then there is overdetermination. Therefore, either mental causes are identical to physical causes (reductionism), or mental causes are epiphenomenal (causally inert).

He sees this as a defeater for non-reductive physicalism, which holds that the mental is not reducible to the physical, yet somehow depends on the physical, and is still causally efficacious.

According to Kim’s mid-career thinking, the only way to preserve mental causation and avoid epiphenomenalism is that mental properties must be reducible to physical properties—otherwise, they would be causally excluded by physical causes. Here, Kim advocates a reductionist physicalism, from which he supports a form of identity theory for mental states (e.g., pain equals C-fiber firing), which in turn allows mental states to be causally efficacious without violating physical causal closure.

Shifts in Kim’s Position

Notably, over the course of his stellar career, Kim changed his approach to the mind-body problem. He began by defending a version of identity theory, then non-reductive physicalism (which relied on supervenience), then a kind of reductive physicalism (returning to a kind of identity theory).

At one point, Kim rejected hard-core physicalism because he could not see how it could provide a sufficient basis for resolving the hard problem of consciousness—accounting for consciousness (qualia) by physical descriptions of the brain alone seemed insurmountable. He said, "Physicalism will not be able to survive intact and in its entirety." Moreover, "phenomenal mental properties are not functionally definable and hence functionally irreducible," and "if functional reduction doesn't work for qualia, nothing will." Thus, there is something of the mind that exceeds that which the brain can generate ("Jaegwon Kim," 2025; Kim, 2010, 2005).

Later, Kim adopted a version of property dualism, although he argued that his position was "something near enough" to physicalism. He still saw physicalism to be the most comprehensive worldview, one that is irreplaceable by any other worldview. Mind, he concluded, is a natural phenomenon, and supernatural explanation only offers "one riddle over another." He believed that any correct explanation for the nature of mind would come from natural science, not from philosophy or psychology ("Jaegwon Kim," 2025, 2005).