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Ryle's book was published three years after ENIAC's birth, and at first glance his ideas would seem to draw strength from the computer age. That, at any rate, is the line Dennett takes in defending his teacher's school of thought. Dennett notes that AI is progressing, creating smart machines that process data somewhat the way human beings do. As this trend continues, he believes, it will become clearer that we're all machines, that Ryle's strict materialism was basically on target, that the mind-body problem is in principle solved. The title of Dennett's 1991 book says it all: Consciousness Explained.
Dennett's book got rave reviews and has sold well, 100,000 copies to date. But among philosophers the reaction was mixed. The can-do attitude that was common in the decades after Ryle wrote--the belief that consciousness is readily "explained"--has waned. "Most people in the field now take the problem far more seriously," says Rutgers University philosopher Colin McGinn, author of The Problem of Consciousness. By acting as if consciousness is no great mystery, says McGinn, "Dennett's fighting a rearguard action."
McGinn and Chalmers are among the philosophers who have been called the New Mysterians because they think consciousness is, well, mysterious. McGinn goes so far as to say it will always remain so. For human beings to try to grasp how subjective experience arises from matter, he says, "is like slugs trying to do Freudian psychoanalysis. They just don't have the conceptual equipment."
Actually there have long been a few mysterians insisting that the glory of human experience defies scientific dissection. But the current debate is different. The New Mysterians are fundamentally scientific in outlook. They don't begin by doubting the audacious premises of AI. O.K., they say, maybe it is possible--in principle, at least--to build an electronic machine that can do everything a human brain can do. They just think people like Dennett misunderstand the import of such a prospect: rather than bury old puzzles about consciousness, it resurrects them in clearer form than ever.
Consider, says Chalmers, the robot named Cog, being developed at M.I.T.'s artificial-intelligence lab with input from Dennett (see following story). Cog will someday have "skin"--a synthetic membrane sensitive to contact. Upon touching an object, the skin will send a data packet to the "brain." The brain may then instruct the robot to recoil from the object, depending on whether the object could damage the robot. When human beings recoil from things, they too are under the influence of data packets. If you touch something that's dangerously hot, the appropriate electrical impulses go from hand to brain, which then sends impulses instructing the hand to recoil. In that sense, Cog is a good model of human data processing, just the kind of machine that Dennett believes helps "explain" consciousness.