Wednesday, 9 May 2012

Mary and the black and white room

Is there 'something-it-is-like' to see red, over and above the
 physical facts about red? The Mary story suggests that there is.

Imagine a scientist named 'Mary.' She lives 200 years in the future, at a time when physics has finally explained everything it can about the physical universe. Mary is an expert in her field, and knows every truth there is to be known about the physical world.

Furthermore,  Mary has lived in a black and white room all her life, and has never seen anything coloured. In this room, she has gained all her scientific knowledge from birth, and conducted all the experiments and discoveries that have made her famous. She knows everything there is to know about the world through science; in particular, she knows all there is to know about the workings of the human brain, including how it forms beliefs, how humans perceive redness, and all the rest.

Mary steps out of her black and white room and immediately apprehends the world in all its colour; the first thing she sees is a red rose. Mary, despite having a grasp on every single piece of scientific knowledge in the world, has learned something new on stepping out of the room: she has learned what it is like to see the colour red.

What is this story supposed to prove? What does it actually prove? Philosophers have been debating this ever since Frank Jackson published a paper in which he introduced the example. Mary represents the perfect scientist, and the totality of the knowledge of all physical facts about the world. Yet as she apprehends colour for the first time, she learns a new fact about the world which she did not know before: what it is like to see the colour red. Before she left her room, Mary knew all scientific, physical facts about how a human being sees an red object, and how the light reflects off that object and into the eye of the human being, creating a red sensation. However, nothing she knew from this position of total expertise could have told her what it is actually like to see a red object from the first-person perspective; she had to leave the room and actually see a red object to grasp this.

The example attempts to show that once all the physical facts are in, some things are left unexplained. All the physical facts about colour do not entail the facts about what it is like to experience colour; and thus we cannot explain what it is like to see colour purely in terms of physical facts. The example is not specific to colour: Jackson generalises it to all conscious experience. Mary can be re-cast as knowing all the facts about rough objects, and how they are felt to be rough; but only when she leaves her perfectly smooth room can she know what it is like to feel a rough object. The example applies to what it is like to see colour, hear sound, touch objects, or taste. In a nutshell, the heart of human conscious experience; in philosophical terms, 'Qualia.'

If Mary really does learn a new fact about the world when she leaves her room, then it follows that what she knew before leaving the room (every physical fact about the world) was not enough to explain some other fact: it follows that there are non-physical facts, facts about conscious experience that are not entailed by physical facts. This suggestion has profound implications for how we think about conscious experience and its place in the physical world: physicalism / materialism is false.

David Chalmers lays out the argument in clear, simple terms:
  1. Mary knows all the physical facts
  2. Mary does not know all the facts
  3. Therefore, the physical facts do not exhaust all the facts.

See also: Zombies, and the Explanatory Gap.

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