The Knowledge Argument begins with the following description of a woman called “Black and White Mary.” Black and White Mary is unusual in two ways. First, she is the world’s most distinguished colour scientist. She knows everything about the physics of colour, about the ways in which light of different wave lengths is reflected from objects, about the ways in which the different wavelengths correspond to the different colours, and so on. She also knows everything about the neurophysiology of colour perception – about the workings of cones in the eye, about the neural signals travelling from the cones to the visual processors in the brain, and about the structures and modes of functioning of the visual processors. Second, although she is not colour blind, Black and White Mary has never experienced colour. She has always lived in a black and white room, viewed the external world through a black and white TV monitor, and eaten food that had been dyed black and white, and so on.
Suppose now that for the first time Mary opens the door to her room and enters the Great World, and that the first thing she sees is a banana. Surely she comes to know something then that she had not known before – what yellow things actually look like, the Qualia. Before she knew that yellow things reflect light waves of such and such wavelength, and she knew how the eyes and brain process information about that wavelength, but a colour blind person could know all of this stuff. What Mary now knows, and what the colour blind person will never know, is how yellow things appear, or what it is like to see something yellow.
First premise: Before Mary left her black and white room; she knew all of the physical facts about colour and colour perception.
Second premise: Yet there was a fact about colour that she didn’t know – the fact that yellow things look a certain way.
Third premise: If it is possible to know all of the members of a certain set S of facts without knowing a given fact, f, f is not identical with any of the members of S.
Conclusion: The fact that yellow things look a certain way is not identical with any of the physical or neurophysiological facts about colour and colour vision.
We now ask ourselves, Has Mary learnt something new, has she had a new experience? If we answer "yes" to this question, then we have committed ourselves to property dualism. If Mary has exhausted all the physical facts about experiencing colour prior to her going out the room, then her encounter with some new property of colour upon experiencing its , reveals that there must be something about the experience of colour which is not captured by the physicalist picture that Mary originally knew. Some properties of colour must therefore be non-physical.
This supports the idea that the mind is a non-physical property of the physical entity, the brain.
A second argument that seeks to show that property dualism is superior to other arguments is the Grain Theory:
The point of this argument is that pain or any other sensory states have different “grain” or constituent structure than brain states. Pain is a simple, unanalyzable property, but brain states are structural characteristics, in the sense that they entail the existence of microentities interacting with one another causally in various ways.
First premise: Every pain is resolvable into simple constituents that are unanalyzable.
Second premise: Every brain state corresponding to a pain, including every brain state corresponding to a simple pain, is analyzable into a large number of particulate objects interacting causally with one another.
Lemma: Hence, simple pains have a property that brain states lack – the property being unanalyzable.
Third premise: If x has a property that y does not have, then x is not identical with Y.
Conclusion: Pains are not identical with brain states.
Would it be possible to reply by saying that pain might be analyzable in reality even
though it doesn’t seem analyzable to us? No. This would make sense only if it was
possible to draw an appearance/reality distinction with respect to pains. Therefore mental and physical states have two different properties.
