What Mary Didn't Know.** Mary is confined to a black-and-white room, is educated through black-and-white books and through lectures relayed on black-and white television. In this way she learns everything there is to know about the physical nature of the world. She knows all the physical facts about us and our enviroment, in a wide sense of 'physical' which includes everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including of course functional roles. If physicalism is true, she knows all there is to know. For to suppose otherwise is to suppose that there is more to know than every physical fact, and that is what physicalism denies.
Physicalism is not the noncontroversial thesis that the actual world is largely physical, but the challenging thesis that it is entirely physical. This is why physicalists must hold that complete physical knowledge is complete knowledge simpliciter. For suppose it is not complete: then our world must differ from a world, W(P), for which it is complete, and the difference must be in nonphysical facts: for our world and W(P) agree in all matters physical. Hence, physicalism would be false at our world [though contingently so, for it would be true at W(P)].1
It seems, however, that Mary does not know all there is to know. For when she is let out of the black-and-white room or given a color television, she will learn what it is like to see something red, say. This is rightly described as learning--she will not say "ho, hum." Hence, physicalism is false. This is the knowledge argument against physicalism in one of its manifestations.2
**[ Excerpt from Frank Jackson's, "What Mary Didn't Know", in The Journal of Philosophy LXXXIII, 5 (May 1986):291-95.]
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