Property Dualism

Supervenience

X supervenes on Y if and only if a change in Y is necessary for a corresponding change in X to be possible. 

The philosophical zombies argument

P1: It is possible to conceive of a zombie.

P2: A zombie is physically identical to a human, but without the mental property of consciousness.

P3: Conceivability implies the idea that it is metaphysically possible.

P4: Consciousness is a mental property.

P5: If a physical brain without consciousness is conceivable, then consciousness must be separate from the physical.

C: Therefore, property dualism is true.

A zombie world is not conceivable

If consciousness relies on the physical processes in our brain, then a 'zombie' physically identical to a human must have consciousness. We can only conceive of it because we don’t understand it.

What is conceivable may not be metaphysically possible

Just because we can imagine something doesn’t mean it could really exist. One might conceive of a right-angled triangle without a hypotenuse but that’s impossible once we know Pythagoras' theorem. It was conceived before it was understood, therefore, conceivability doesn’t guarantee metaphysical possibility.  

What is metaphysically possible tells us nothing about the actual world

Even if a zombie world is metaphysically possible, that doesn’t prove that it is actually true of our world. It’s possible unicorns could exist, but that doesn’t mean they do, and it doesn't mean they're relevant to the real world.

The Mary argument

P1: Someone who knows everything physical about colour without seeing it would have 100% physical knowledge.

P2: Upon seeing colour for the first time, they would gain knowledge.

P3: This cannot be physical knowledge since they already have 100% of this.

C: Therefore, there is non-physical knowledge, and physicalism is false.

Mary gains ability knowledge (objection)

When Mary leaves her black-and-white room and sees colour, she gains no new propositional knowledge. Instead, she gains new ability knowledge: the ability to recognise or imagine red, the ability to remember red, the ability to compare shades of red

Mary gains acquaintance knowledge (objection)

When Mary sees colour for the first time, she becomes acquainted with a new property: the qualia of seeing red.

Mary finds a new way to know her knowledge

Mary just comes to know her physical knowledge under a new mode of presentation. She already knew all the physical facts about colour vision, but lacked the qualia to represent them from the first-person perspective.

Property Dualism

At least some mental properties are not reducible to, nor dependent on, physical properties.

Example of supervenience

A painting’s beauty cannot change without a corresponding change in the physical arrangement of paint or light.

Property dualism against supervenience (mental on physical)

Mental states could change without any change in the brain. Therefore, two physically identical brains could have different mental states

Philosophical zombies

Beings physically identical to humans but with no consciousness.

Key claim of the zombie argument

If zombies are conceivable, consciousness must non-physical.

Key claim of the Mary argument

Physicalism is false because Mary learns something non-physical when she sees colour.