Questions: Property Dualism and Non-Physical Properties

Question 1

A student argues: 'Property dualism solves the interaction problem because mental and physical properties both belong to the same substance — there's no barrier to cross.' What challenge does this response fail to address?

• A. Property dualism still posits two distinct substances, so the interaction problem remains unchanged
• B. The student is correct; property dualism fully dissolves all the problems of substance dualism
• C. If every physical effect already has a complete physical cause, non-physical mental properties appear causally redundant — the exclusion problem — even without a substance barrier
• D. Mental properties would need to be identical to physical properties to exert any causal influence, which property dualism denies

Answer: (C)

Property dualism does solve the interaction problem by placing mental and physical properties in the same substance. But it faces the exclusion problem: if the physical world is causally closed (every physical effect has a sufficient physical cause) and mental properties are non-physical, then mental properties have no causal work to do. The physical cause already fully explains the effect. The student's response addresses interaction across a substance gap but misses this separate problem about causal relevance in a causally closed physical world.

Question 2

Epiphenomenalism holds that mental properties are caused by physical states but have no causal power of their own. What is the strongest objection to this view?

• A. It makes mental properties identical to physical properties, which collapses into reductionism
• B. It implies that consciousness is an illusion, which is self-refuting for any conscious reasoner
• C. If mental properties are causally inert byproducts, their evolutionary persistence is unexplained — selection pressure should eliminate costly neural processes that produce effects with no causal consequences
• D. Epiphenomenalism requires accepting substance dualism as its foundation

Answer: (C)

The evolutionary argument is widely considered the strongest objection. If conscious mental properties are causally inert — mere shadows of neural events — then evolution would have no mechanism to preserve them. Selection acts on behavior, which is physical; causally inert properties cannot contribute to survival or reproduction. The persistence of consciousness across the animal kingdom therefore demands explanation that epiphenomenalism cannot provide. Options A and D are factually wrong; B is a philosophical objection but not the strongest empirical one.

Question 3

Property dualism avoids most of the problems of substance dualism by accepting mainly one substance.

• T. True
• F. False

Answer: False

Property dualism avoids the interaction problem (how two substances communicate) but introduces its own severe problem: the exclusion problem. If mental properties are non-physical and the physical world is causally closed, mental properties appear causally redundant. Property dualism trades one problem for another rather than dissolving dualist difficulties. It occupies a 'precarious middle ground' — more defensible than substance dualism in some respects, but not problem-free.

Question 4

According to the knowledge argument, when Mary the color scientist sees red for the first time, she acquires new knowledge — which suggests that her complete prior physical knowledge was missing something, supporting the claim that mental properties are not fully physical.

• T. True
• F. False

Answer: True

This is the structure of the knowledge argument for property dualism. The premises: (1) Mary knew all physical facts about color perception before leaving her black-and-white room. (2) When she sees red, she learns something new — what it's like to see red. (3) Therefore, what she learned was not contained in the physical facts. (4) Therefore, there are facts about conscious experience that are not purely physical — mental properties are irreducibly non-physical. The argument is disputed but the logical structure is valid if the premises are accepted.

Question 5

What is the exclusion problem, and why does it threaten to collapse property dualism into the epiphenomenalism it was meant to avoid?

Model answer: The exclusion problem (developed by Jaegwon Kim) arises from two commitments: (1) causal closure — every physical effect has a sufficient physical cause; and (2) non-identity — mental properties are not identical to physical properties. Together, these imply that when a mental property and a physical property are both present when a physical effect occurs, the physical cause already fully explains the effect. There is no causal gap for the non-physical mental property to fill — it is causally redundant. This is precisely epiphenomenalism: mental properties are present but causally inert. Property dualism was supposed to preserve the genuine causal relevance of mental properties while avoiding substance dualism's interaction problem — but the exclusion problem suggests it cannot achieve both.

The dilemma is sharp: either mental properties are identical to physical properties (reductionism), or they are causally redundant (epiphenomenalism). Non-reductive physicalism tries to escape by arguing that mental properties are 'multiply realizable' or that mental causation operates at a different level of description — but Kim's challenge is whether these moves genuinely secure causal relevance or merely redescribe the problem.