Originally posted by Zero
So, how do you know that you are percieving it correctly, in order to state that it cannot arise from the purely physical?
It's not a question of 'correct' or 'incorrect.' I imagine you are planning to say that it could just be an illusion. But that would not get us anywhere, because then we would have the same problems explaining the illusion itself.
What is that problem? One way to phrase the problem is that subjective experience possesses intrinsic properties, whereas our physical theories speak only of extrinsic properties. The objective notion of length, for example, has no meaning if I do not have some reference marker with which to compare quantities of length. However, my subjective notion of 'redness' does not come by way of comparison or reference to other colors or concepts; it is self-defining, in a way, and so it is said to have an intrinsic quality.
For instance, suppose you are floating in the center of a large, uniformly lit (such that there are no shadows or gradations of color), atmosphereless white sphere with nothing in it but yourself. (You can survive because you are in a space suit, although you cannot remove any part of your suit.) Suppose that you and the sphere are stationary, so you cannot approach its edge. Can you tell how wide the sphere is? No, you can't, because you have no references with which to compare it. You cannot go up to it and measure its circumference with a tape measure, you cannot calculate how far its edge is from you by yelling and estimating the time delay of the echo, and so on. In the absence of a reference, the sphere's width is undefined to you; not surprising, since extension is an extrinsic property. At best, you know it is at least a bit bigger than yourself, but you only know that by way of reference to your own body's physical dimensions.
But you
can perceive that the sphere is white. You do not have to compare its color to anything else to know this; you don't have to look down at your boot and say "OK, now that I see both my boot and the sphere, I can tell that the sphere is white." You simply perceive its white-ness, and even in the absence of any other reference colors, you know it is white. That is because your perception of the sphere's color is an intrinsic property.
So if subjective experience is to be physical, that is equivalent to saying that there must be some way to get intrinsic properties from extrinsic properties. But this is not possible. We cannot use a set of things that are inherently defined with respect to other things to create something that is entirely defined by itself. The best we can do from a set of extrinsic (relational) properties is create more complex chains of relations, but we can't somehow manipulate relationships to get something that is characterized by its lack of relationship with anything else.
