Jaegwon Kim's causal exclusion argument threatens non-reductive physicalism: if every physical effect has a sufficient physical cause, distinct mental causes would systematically overdetermine those effects. Non-reductionists objected that this relies on a problematic notion of causal sufficiency (physically sufficient phenomena must span cross-sections of the backwards light cone and be maximally specific, so they are poor candidates for causes). Bram Vaassen (2021) answered by reformulating the argument with Physical Closure and Physical Exclusion, premised on physical rather than causal sufficiency, and conceded that the reformulated argument inherits familiar unresolved problems: the disputed plausibility of Physical Exclusion itself (does it wrongly exclude supervenient-but-distinct causes and paradigmatic higher-level causes such as hurricanes, infections, and banking crises?), its determinism-friendly formulation, and an auxiliary assumption needed to derive genuine causal overdetermination. The open problem is to adjudicate the soundness of this reformulated exclusion argument: whether Physical Exclusion survives its counterexamples under the supervenience-compatible reading of distinctness, whether the argument extends to probabilistic physical sufficiency, and whether the auxiliary assumption holds across competing accounts of causation — thereby determining which premise, if any, non-reductive physicalism must abandon.

Background

Mental causation is the claim that mental phenomena (beliefs, desires, intentions) are causes of physical happenings, such as bodily movements. Non-reductive physicalism — the dominant position in philosophy of mind — holds that mental phenomena are not identical to physical phenomena while still depending on them: each mental phenomenon metaphysically supervenes on (has its nature fully fixed by) its underlying physical base. A neighboring anti-reductionist position is emergentism, on which higher-level phenomena arise from and depend on their physical bases while remaining genuinely novel — a position recently defended as deserving serious consideration (Zhong 2020). Jaegwon Kim's exclusion argument (Kim 1989, and subsequent work) purports to show this combination is unstable. Its canonical premises are Causal Closure (every physical effect has a sufficient physical cause), Causal Exclusion (no two distinct causes can both be non-overdetermining causes of the same effect), Non-Reductionism, Mental Causation, and a denial of systematic overdetermination; together they force the conclusion that non-reductive physicalism is false. Here 'genuine overdetermination' means two independently sufficient causes of one effect, like two bullets simultaneously killing one victim — possible as a coincidence, but wildly implausible as a systematic pattern. A central line of criticism targets the notion of causal sufficiency: for a physical phenomenon to be sufficient (on its own, by physical law) for an everyday effect, it must exclude interference from arbitrarily far away, so it must span vast regions of space (a cross-section of the effect's backwards light cone — the region from which light-speed interference could arrive) and be maximally specific in its physical detail. Such enormous, maximally specific phenomena are poor candidates for causes, since causes in everyday and scientific explanation (infections, hurricanes, throws of rocks) are local and coarse-grained difference-makers: their absence would correlate with the effect's absence, whereas no light-cone-spanning phenomenon has that property (List & Menzies 2009; Raatikainen 2010). Vaassen (2021) argued these objections are superficial: the exclusionist can replace causal sufficiency with physical sufficiency — phenomenon A is physically sufficient for B iff every physically possible world containing A also contains B, a purely modal relation that claims nothing about A being a cause. The reformulated premises are Physical Closure (for any physical effect and time t, some physical phenomenon A occurring at t is physically sufficient for it), Physical Exclusion (if A occurring at t is physically sufficient for B, no phenomenon C occurring at t that is distinct from A and from all of A's parts is a cause of B, unless it is genuine overdetermination), plus Physical Parts (any part of a physical phenomenon is itself physical), Non-Reductionism, Mental Causation, and Non-Overdetermination; the six are jointly inconsistent, so one must go. Three features of this reformulation remain contested. First, Physical Exclusion inherits the classic objections to exclusion principles: Bennett (2003), Schaffer (2003), and Sider (2003) argue that phenomena supervening on, yet numerically distinct from, physical phenomena can be genuine non-redundant causes, and Block (2003) and Bontly (2002) object that any such principle would wrongly exclude patently causal higher-level phenomena — hurricanes, infections, banking crises — since these are just as distinct from any physically sufficient phenomenon as mental phenomena are. Second, Physical Closure is stated assuming determinism; the noted relaxation — physical sufficiency for the probability of the effect rather than its occurrence — has not been worked through, and how the modal definitions and the exclusion reasoning fare under probabilistic or indeterministic physics is open. Third, deriving causal (not merely physical) overdetermination from Physical Exclusion requires an auxiliary assumption: that any physically sufficient physical phenomenon A contains a sub-phenomenon a that is a bona fide cause of the effect against the background of the rest of A, an assumption whose acceptability varies across competing theories of causation (production-based accounts, on which causes generate effects, versus dependence-based or interventionist accounts, on which causes make a difference to their effects under interventions). Finally, even setting the sufficiency question aside, the broader dispute over which metaphysical dependence relation between mental and physical phenomena — supervenience, realization (the view that a mental instance is a proper part of its physical realizer, as in Zhang 2022), constitution, or grounding (a primitive metaphysical dependence relation prominent in recent metaphysics, as in Pineda-Oliva 2022 and Moorfoot 2025) — is compatible with causal efficacy remains unresolved.

Problem Statement

Determine whether the causal exclusion argument, reformulated in terms of physical sufficiency (Physical Closure and Physical Exclusion in place of the causal-sufficiency premises, together with Physical Parts, Mental Causation, Non-Reductionism, and Non-Overdetermination), is sound against the prominent forms of non-reductive physicalism — the forms on which mental phenomena are not identical to, but metaphysically supervene on, their underlying physical phenomena. Adjudicating this requires resolving three linked questions. (i) Is Physical Exclusion true under this reading of 'distinct': do the counterexamples from supervenient-but-non-identical causes (Bennett, Schaffer, Sider) and the reductio from patently causal higher-level phenomena such as hurricanes, infections, and banking crises (Block, Bontly) defeat the principle, or is there a principled criterion — not case-by-case fiat — under which it survives them? (ii) Does the argument survive restatement for probabilistic physical sufficiency, where Physical Closure guarantees only a physical phenomenon sufficient for the probability of the effect rather than its occurrence, given that the modal definitions and the exclusion reasoning must be reworked without assuming determinism? (iii) Is the auxiliary assumption needed to derive genuine causal overdetermination — that any physically sufficient physical phenomenon contains a sub-phenomenon that is a bona fide cause of the effect against the background of the remainder — acceptable across competing accounts of causation (production-based and dependence-based alike)? The resolution is either that the salient forms of non-reductive physicalism must abandon one of the six propositions, or that the reformulated argument is unsound.

References

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