1. Substance and Property Dualism
Michael Lacewing

2. Metaphysics of mind Substance: needs no other thing to exist
Dualism: there are two sorts of substance, mind (or soul) and matter
Mental properties are properties of a mental substance
Materialism: there is just one sort of thing, matter
Mental properties are properties of a material substance

3. Materialism and mental properties
Substances can have different sorts of properties
Biological: swan
Colour: white
But both physical properties
Property dualism: mental properties are not physical properties
Hmm…

4. Descartes’ dualism The mind is a separate substance from the body.
What am I? I am a thing that thinks. I cannot doubt this, yet I can doubt whether I have a body. So I can be separated from a body.
The body has parts, the mind has no parts. So they are different kinds of thing.

5. Objections Descartes has not shown that he (the mind) is a substance.
Just because Descartes can think of his mind existing without his body, this doesn’t mean that his mind really can exist without his body.
Cp. I think the Masked Man robbed the bank; I don’t think my father robbed the bank; Therefore, my father isn’t the Masked Man.
We can’t infer real possibility directly from what we can imagine.

6. Mental causation
If the mind is just thought, not in space, and matter is just extension, in space, how could one possibly causally affect the other?
All physical effects have a sufficient physical cause. Nothing physical happens needs a non-physical explanation.
Mental causes would violate the laws of physics, e.g. law of conservation of energy.

7. Jackson’s knowledge argument
Mary, a neuroscientist, has never seen colour, but knows all about colour perception
Mary doesn’t know what it is like to see red - so, although Mary knows all the physical facts about seeing red, there is a fact (of consciousness) Mary doesn’t know
Therefore, properties of consciousness are not physical properties

8. Reply
Mary doesn’t learn a new fact, but a new way of thinking about an old fact. She now knows the fact of what happens in the brain through introspection.
On concepts and properties: the same fact (the glass contains water) can be thought of in different ways (the glass contains H2O).

9. Zombies
Zombie (in philosophy, not voodoo!): a physical replica of a person, but without consciousness
A zombie has identical physical properties, but different mental properties - therefore mental properties aren’t physical properties
Zombies may not be physically possible, but they are logically possible

10. Reply
Zombies are not possible - that we can imagine them isn’t enough (see objection to Descartes)
Imagine that water is not H2O - it seems we can, but in fact, this is impossible
There could be something just like water, but if it isn’t H2O, it isn’t water

11. Response The analogy doesn’t work
We make the mistake in the case of water, because we imagine something just like water
There is nothing ‘just like’ a zombie which isn’t a zombie
Imagination is a good guide to possibility here - therefore zombies are possible, and property dualism is true