3.4.2 - Property dualism - zombies and Mary

The Pressure On Physicalism

The problem is simple to state and hard to solve: if the world is wholly physical, why is there anything it is like to have an experience?

A complete physical story of colour vision might describe wavelengths, retinal stimulation, neural pathways, information processing, verbal reports, and behaviour. But a property dualist asks whether that story leaves out the felt character of the experience: the redness of seeing red, the hurtfulness of pain, or the taste of coffee.

Three terms need to be stable before the arguments begin.

Chalmers sharpens the pressure by distinguishing the psychological or functional side of mind from the phenomenal side. The psychological side concerns what a state does: discriminating, reporting, remembering, controlling behaviour. The phenomenal side concerns what the state feels like. A physicalist can seem strongest when explaining functions, but property dualism presses the thought that explaining every function may still leave the phenomenal feel unexplained.

The AQA version of property dualism is therefore not a vague claim that mind is mysterious. It is the precise claim that at least some mental properties are not reducible to, and do not supervene on, physical properties.

Property Dualism

Property dualism says that a person or brain need not be a separate non-physical substance, but it can still have non-physical mental properties. The contrast is important:

For example, if pain were reducible to a neural state, then a complete account of that neural state would be a complete account of pain.

If mental properties supervene on physical properties, then two beings that are exactly alike physically must also be exactly alike mentally. Non-supervenience is stronger than non-reduction: it says that the physical facts do not even fix all the mental facts. Here the dependence is logical or metaphysical: complete physical duplication need not necessitate identical mental properties. Contingent psychophysical laws may still make brain events cause mental events. That causal dependence is compatible with property dualism. By contrast, merely irreducible vocabulary with mental properties necessarily fixed by physical properties does not establish the full AQA property-dualist thesis.

For AQA, property dualism is the stronger claim:

1. Some mental properties are not reducible to physical properties.
2. Some mental properties are not supervenient on physical properties.
3. Therefore, a complete physical duplicate could still differ mentally.

The two thought experiments here examine that claim in different ways. The zombie argument asks whether the physical could be the same while consciousness is absent. The Mary argument asks whether complete physical knowledge could still leave out knowledge of phenomenal character.

The Zombie Argument

A philosophical zombie is not a monster. It has the same body, brain processes, functional organisation, speech, and behaviour as its conscious twin, but there is nothing it is like to be it.

Chalmers' point is not that zombies actually exist. The thought experiment is modal: it asks what is possible. If a zombie world is possible, then the physical facts do not necessitate the phenomenal facts. That would mean phenomenal properties do not supervene on physical properties.

Claim at issue: Consciousness is not physical because a complete physical duplicate could lack it.

1. P1: If physicalism is true, then any world physically identical to ours must also be identical in its phenomenal properties.
2. P2: A zombie world is conceivable: a world physically identical to ours but with no conscious experience.
3. P3: If a zombie world is ideally conceivable, then it is metaphysically possible.
4. P4: If a zombie world is metaphysically possible, then phenomenal properties do not supervene on physical properties.
5. Therefore, C: Physicalism is false and property dualism is supported.

Hidden assumption: ideal conceivability is a reliable guide to metaphysical possibility in this case.
Inference type: modal and conceptual; deductive if the conceivability-to-possibility bridge is accepted.
Main pressure point: P2 and P3 carry most of the weight.

Why might P2 look plausible? We can describe every physical and functional fact about a person while still apparently leaving open the question of whether there is experience. The zombie behaves as if it is in pain, says it is in pain, and processes damage signals as we do, yet the thought experiment asks us to subtract the hurtfulness itself.

The argument's force is that physicalism normally requires more than actual correlation. It requires the physical facts to fix the mental facts. If the physical story can be duplicated without consciousness, then consciousness looks like an extra property.

Zombie Responses

AQA specifies three main response routes. Each attacks a different point in the argument.

The first response is the most direct: it says the argument never starts. The second is more concessive: it allows the zombie idea to seem coherent, but blocks the move to possibility. The third is the most revisionary about physicalism: it weakens what physicalism must prove by saying that cross-world possibility is not decisive for actual-world ontology.

For evaluation, do not say simply that zombies are unrealistic. Chalmers is not claiming they are biologically or naturally possible under our laws. The target is metaphysical possibility: whether there could be a physically identical world without consciousness.