Daniel Dennett has an interesting rebuttal to Frank Jackson's argument for qualia. Jackson's argument takes the form of a story about Mary, who--although she has lived in an environment devoid of color since her earliest days--has nevertheless become the world's foremost scientific expert on color, studying the outside world through a black and white monitor. Once Mary leaves the confines of her achromatic environment for the normal, colorful world, she will finally get to see blue things. And, Jackson tells us, she will discover something that she hadn't previously known through her scientific studies. If that is so, then there is more to color than what science can measure and report, and that something more is called qualia.
Dennett counters in Consciousness Explained that if Mary knows absolutely everything there is to know about this color and our perception thereof, then she already knows, in terms of physics, how blue differs from yellow even before she has been released from her colorless confines. After all, her scientific grasp, if it is truly comprehensive, includes the knowledge of how the colors blue and yellow affect her (and other humans). He says,
"She knows black and white and shades of gray, and she knows the difference between the color of any object and such surface properties as glossiness, versus matte, and she knows all about the difference between luminance boundaries and color boundaries (luminous boundaries are those that show up on black-and-white television, to put it roughly). And she knows precisely which effects -- described in neurophysiological terms -- each particular color will have on her nervous system. So the only task that remains is for her to figure out a way of identifying those neurophysiological effects 'from the inside'... for instance... by noting some salient and specific reaction that her brain would have only for yellow or not for red" (p. 400).
Once she has been released from captivity, her knowledge of these differences will enable her to detect right away that a blue-painted banana is not really yellow. If she already knows how she would distinguish blue from yellow even when in the confines of the blueless and yellowless world, then she cannot be said to have learned how to make that distinction only after having left her captivity.
His story of Mary immediately applying the knowledge acquired during her confinement of differences in luminous boundaries between the colors blue and yellow seems a bit of a stretch--but not impossible in principle. What is problematic, however, is the way in which Dennett sweeps the problem pointed out by Jackson under the rug.
Dennett's argument rests in part on Mary's ability to recognize some visible differences even while confined to her colorless laboratory. But that ability itself rests on her perception of black, gray, white and other achromatic-colors (that's a bit of an oxymoron, I know) that she uses in order to study luminance boundaries during her colorless captivity. In other words, Dennett seems to get rid of the need for the quale pertaining to the sensation of blue things by having Mary rely earlier on the qualia pertaining to the sensation of gray, black and white things in order to learn about the luminence boundaries of chromatic objects. As a result, Mary's ability to distinguish blue from yellow once she has left captivity does not seem to depend on the visible properties mentioned in Frank Jackson's argument. But even if Mary can distinguish luminence boundaries instantly, she is doing so only in virtue of her reliance upon visible differences that she has not quantified: in making the distinction that Dennett imagines she might make immediately upon her exit from confinement, Mary relies upon more than her knowledge of the physics of color and sensation. But since this knowledge has been acquired while Mary is still in confinement, Dennett's story amounts to a kind of legerdemain.
To see why Dennett's thought experiment merely hides the problem revealed by Jackson, imagine that while Mary is in the laboratory she learns about luminance boundaries only in third-person, quantified terms but without relying upon vision at all: her laboratory is not only colorless but lightless as well--at least as far as Mary is concerned, for she is blind, but able to perceive, thanks to a device that translates visual images into tactile signals on her back. Instead of leaving a colorless room, she gets a surgery allows her to see for the first time through her eyes. Wouldn't her post-operative encounter with blue and yellow seem a bit more novel than it does in Dennett's story? To learn how to apply the general, quantitative, scientific knowledge she already has to the immediate particular cases, Mary would have to rely upon phenomenologically novel qualitative differences in the visible objects that confront her. She may even have to pose questions to others in order to be sure of how to name the things that are before her, even though she has previously studied them. In learning how to relate her new experiences to previously possessed knowledge, Mary will be acquiring a sort of knowledge that she couldn't have gotten from a textbook --or at least not from a braille textbook. Mary, who already knew everything there is to know about the physics of color, will be learning something new.
Dennett counters in Consciousness Explained that if Mary knows absolutely everything there is to know about this color and our perception thereof, then she already knows, in terms of physics, how blue differs from yellow even before she has been released from her colorless confines. After all, her scientific grasp, if it is truly comprehensive, includes the knowledge of how the colors blue and yellow affect her (and other humans). He says,
"She knows black and white and shades of gray, and she knows the difference between the color of any object and such surface properties as glossiness, versus matte, and she knows all about the difference between luminance boundaries and color boundaries (luminous boundaries are those that show up on black-and-white television, to put it roughly). And she knows precisely which effects -- described in neurophysiological terms -- each particular color will have on her nervous system. So the only task that remains is for her to figure out a way of identifying those neurophysiological effects 'from the inside'... for instance... by noting some salient and specific reaction that her brain would have only for yellow or not for red" (p. 400).
Once she has been released from captivity, her knowledge of these differences will enable her to detect right away that a blue-painted banana is not really yellow. If she already knows how she would distinguish blue from yellow even when in the confines of the blueless and yellowless world, then she cannot be said to have learned how to make that distinction only after having left her captivity.
His story of Mary immediately applying the knowledge acquired during her confinement of differences in luminous boundaries between the colors blue and yellow seems a bit of a stretch--but not impossible in principle. What is problematic, however, is the way in which Dennett sweeps the problem pointed out by Jackson under the rug.
Dennett's argument rests in part on Mary's ability to recognize some visible differences even while confined to her colorless laboratory. But that ability itself rests on her perception of black, gray, white and other achromatic-colors (that's a bit of an oxymoron, I know) that she uses in order to study luminance boundaries during her colorless captivity. In other words, Dennett seems to get rid of the need for the quale pertaining to the sensation of blue things by having Mary rely earlier on the qualia pertaining to the sensation of gray, black and white things in order to learn about the luminence boundaries of chromatic objects. As a result, Mary's ability to distinguish blue from yellow once she has left captivity does not seem to depend on the visible properties mentioned in Frank Jackson's argument. But even if Mary can distinguish luminence boundaries instantly, she is doing so only in virtue of her reliance upon visible differences that she has not quantified: in making the distinction that Dennett imagines she might make immediately upon her exit from confinement, Mary relies upon more than her knowledge of the physics of color and sensation. But since this knowledge has been acquired while Mary is still in confinement, Dennett's story amounts to a kind of legerdemain.
To see why Dennett's thought experiment merely hides the problem revealed by Jackson, imagine that while Mary is in the laboratory she learns about luminance boundaries only in third-person, quantified terms but without relying upon vision at all: her laboratory is not only colorless but lightless as well--at least as far as Mary is concerned, for she is blind, but able to perceive, thanks to a device that translates visual images into tactile signals on her back. Instead of leaving a colorless room, she gets a surgery allows her to see for the first time through her eyes. Wouldn't her post-operative encounter with blue and yellow seem a bit more novel than it does in Dennett's story? To learn how to apply the general, quantitative, scientific knowledge she already has to the immediate particular cases, Mary would have to rely upon phenomenologically novel qualitative differences in the visible objects that confront her. She may even have to pose questions to others in order to be sure of how to name the things that are before her, even though she has previously studied them. In learning how to relate her new experiences to previously possessed knowledge, Mary will be acquiring a sort of knowledge that she couldn't have gotten from a textbook --or at least not from a braille textbook. Mary, who already knew everything there is to know about the physics of color, will be learning something new.
Comments