Michael Egnor, a substance dualist, finds himself in the midst of a fascinating debate with materialist neuroscientist Steven Novella.
Substance dualists hold that the world is reducible to at least two fundamental substances: mind and matter. Materialists belive that everything is reducible to matter and that there is no such thing as mental substance.
Novella asserts that Egnor's view that mind is an immaterial entity that plays a role in cognition and consciousness has been discredited by scientific advances in neuroscience:
[Egnor] fails to recognize that this battle has already been fought and lost within the scientific arena...[a]s our knowledge of brain function increases, it is squeezing out any role for a non-material ghost in the machine. A non-material cause of mind is...unnecessary...
Novella believes that mind is just a word that we use to describe the function of the brain, much like we use the word "digestion" to describe the function of the stomach. Here is part of Egnor's reply:
There are six properties generally agreed to constitute the essence of mental states: intentionality, qualia, persistence of self-identity, restricted access, incorrigibility, and free will. Each of these properties of the mind shares a common characteristic - subjectivity, what philosopher David Chalmers has called the "Hard Problem" of consciousness. The 'easy problems' of consciousness are the kinds of problems that neuroscientists routinely deal with; for example, the determination as to which neurotransmitters in the brainstem are associated with behavioral arousal. These are 'easy' because they're tractable, although they can obviously involve some very challenging science. The Hard Problem is something entirely different; it is the problem of subjective experience, of why we are subjects, and not just objects. Why do we experience things?
Philosopher Joseph Levine has termed this epistemological gap between our subjective experience and our inability to explain it using a materialistic understanding of nature the "Explanatory Gap." Levine succinctly observes that we lack an explanation of the mental in terms of the physical.
The dispute comes down to this question: How can subjectivity be explained by objective matter? Subjective experience is the central dilemma in the mind-brain problem. Matter, even brain matter, has third-person existence; it's a 'thing.' We have first-person existence; each of us is an 'I,' not just a thing. How can objective matter fully account for subjective experience? If matter is the complete cause of the mind, how is it that none of the six salient properties of the mind is a property of matter? How exactly does a clump of protein, carbohydrates, and lipids (a neuron) give rise to meaning or to first person experience - using the example of pain, not merely the behavior associated with pain and the reflexes and neural correlates of pain, but the experience of it?
The mind's salient properties are all first-person, not third-person. Not a single first-person property of the mind - not intentionality, qualia, persistence of self-identity, restricted access, incorrigibility, nor free will - is a known property of matter. No one has ever demonstrated a law-like dependence of any subjective property of the mind on any objective property of matter. How could we establish such a scientific relationship? A differential equation quantitatively relating intentionality to intracellular calcium?
Egnor poses a tough challenge to the materialist. How does matter convert photons of energy into the experience of red? How does matter convert vibrations of molecules in air to the experience of sound? Before the materialist can claim victory he needs to be able to give a plausible explanation of how material substance can give rise to the phenomena of subjective experience. Without such an explanation all claims that the issue has been settled seem grossly premature.RLC