Perhaps one of the most exciting trends in current philosophy of mind is the renewed interest in what David Chalmers calls the really hard problems of consciousness. “While it was once assumed that the apparently prickly issue of consciousness would yield fairly easily to advances in neurophysiology and computational models, as this century draws to a close our conscious minds remain mysterious. The seeming imperviousness of consciousness to traditional scientific methods has prompted not only philosophers but scientists as well to re-evaluate the facile optimism which characterized the field previously. Chalmers, in The Conscious Mind, has taken us to the heart of the current debate.
Chalmers has two aims: he wants to take consciousness seriously, and he wants to take science seriously. He begins by challenging the notion — accepting as dogma by most scientists — that conscious experience can be reductively explained. Pointing out that reductive explanations explain high-level phenomena by providing a structural or functional analysis at lower-levels, he asks the simple question: How could consciousness possibly be explained this way? Here he draws a distinction between the purely psychological — the lower-level brain activities which accompany consciousness — and the phenomenological — the higher level conscious experiences as they appear to us. With this distinction, Chalmers argues that reductive explanations of mind give psychological answers to phenomenological questions. Phenomenological questions ask about consciousness qua consciousness, about the particular quality of consciousness considered in itself, while psychological answers specify systems of neurons and physical processed within the brain. As explanations of the same thing, Chalmers believes the two are incommensurable. Given any psychological explanation of consciousness, the phenomenal question is always left unanswered: But why does consciousness have the particular qualities that it does? How can a structure or function in the brain tell me why red looks red; blue looks blue; pain have its particular quality in my mind, and so on? To this question, he concludes, current science cannot speak, and so, to use the popular phrase of Wittgenstein, it must remain silent.
At least for now. Chalmers’ ultimate goal is to show how an appropriately expanded science could incorporate consciousness. To make his case, he must first debunk the doctrine of materialism itself. Appealing to thought experiments utilizing zombies, inverted spectrums, and neuron replacement with silicon chips, Chalmers argues that all of the physical facts about the universe could be known in detail, while the facts about consciousness could remain unknown. Consider his zombie twin — an imaginary physical replica of himself which differs only in that it lacks consciousness. While he admits that such a being is probably not actually possible, he argues that it is still logically possible. This seems true enough. I can imagine a replica of myself, possessing all of the physical facts about my body and brain down to the smallest detail, and yet having no consciousness whatever. According to Chalmers, my zombie twin would act, think, and speak exactly as I do, only the lights would be off inside. The conclusion? Physical facts cannot logically entail facts about consciousness, and so materialism — the doctrine that physical facts must logically entail all facts (since physical facts are all there is) — cannot be true. As Chalmers puts it, after God fixed all physical facts about the universe, He still had more work to do — He had to fix the facts about consciousness.
Chalmers speaks of God in a metaphorical sense. He does not want to bring back that great bane of contemporary science, the immaterial mind or soul. What he wants is to consider consciousness itself as a fundamental property of an expanded, yet still naturalistic, scientific framework. Just as mass, momentum, and energy are irreducible, so too is consciousness itself. So if consciousness is to be taken seriously, science must simply get used to the fact that it is not a reducible feature of the universe. But the new science will still do what the old one has done — incorporate the novel property and find the laws (psychophysical laws, as he calls them) which relate the property to the rest of the system. All is well.
Not really. One of the straight-away consequences of Chalmers’ argument is the rather unpalatable problem of epiphenomenalism — the position that our conscious minds are causally influenced by our physical brains but cannot themselves exert any causal influence. Chalmers apparently does not see much of a need to take the problem of epiphenomenalism seriously, commenting that, if his arguments are sound, then we may simply have to get used to it. A tension in his work is therefore revealed: epiphenomenalism is counter-intuitive in the extreme. I do not think, for instance, that when my hand is burned by a flame, my conscious experience of pain has nothing to do with the decision to pull my hand away. Indeed, our decisions and judgments seem to follow directly from our conscious experiences. According to Chalmers, our intuition that our conscious minds exert a causal influence on our behavior may turn out to be smoke and mirrors. His argument is therefore ironic: while he begins by resolving to take the problems of mind seriously, he ends with a position that no one can take seriously.
The problem for Chalmers is that he is committed to taking science seriously as well, which he believes necessitates a belief in the absolute causal determinacy of the physical world. Science apparently establishes that the physical world is, as he puts it, causally closed. Every physical event has a sufficient physical cause (this is the definition of scientific determinism). From this, it follows that any influence from the mind is impossible. Given the premise of causal closure, his argument is consistent. But thoughtful readers could wonder: Might it be the case that the physical world is not absolutely determined? Chalmers denies this possibility emphatically; indeed, the presumption of causal closure is one of the key constraints of his theory. Whether in his idealized thought experiments with zombies, or in the real world of people, Chalmers argues that determinism is part and parcel of physical reality. What is physical, is determined. While his initial arguments against materialism are brilliant and persuasive, his allegiance to determinism becomes problematic. By maintaining that consciousness is a fundamental property in an expanded physical domain, it can not act independently of that domain, anymore than other physical properties such as mass or momentum. There is no way our conscious minds can act. We are left with epiphenomenalism. Consciousness may indeed be beyond materialism, but it remains a passive feature of a physical framework, and as such carries no causal efficacy. The common thread here is that whatever model he considers, whether expanded or otherwise, it must remain determined. To suggest otherwise would be to travel outside the bounds of science.
But could Chalmers be taking science too seriously? Does it follow from science that the physical world must be deterministic? Chalmers evidently takes this position as incontrovertible. Consequently, he neglects to seriously consider a very real possibility: What if human behavior is not determined by the physical domain? What if his zombie (if it could exist), having only physical facts but lacking a conscious mind, could not think, speak, or behave as a conscious person? Perhaps the conscious mind is causally necessary for reproducing human behavior at all! Chalmers does not take this possibility seriously, and so we are left to ourselves to consider the alternatives that could arise (an answer to epiphenomenalism) by challenging not just materialism but scientific determinism as well.
Nevertheless, The Conscious Mind goes a long way toward re-instating serious discussions about consciousness. As the hard problems of mind are taken seriously, we can expect richer and more fruitful theories to emerge. Chalmers has taken the first step. Perhaps the next step is to consider that mind, among all of its other splendid mysteries, might also exert a causal influence on the physical world. In this case, we shall have to take seriously not just the our current picture of science but its inevitable limitations as well. We may even live to see the day when free will itself is resurrected as a topic worth taking seriously. In this case, our picture of science will expand indeed.