To my mind, the true implications of Philosophy of Mind, far from being an argument against Theism, are actually an argument for Theism. To see this, we must start, not with God's mind, but our own.
It is indisputable that Consciousness exists. Or rather, it has been disputed, but it ought never to have been. However many fallacies Descartes may have committed later in his arguments, I think therefore I am has always seemed perfectly sound to me. It is in fact more certain than anything else.
What would it mean to say that I am wrong about being self-aware? That would require me to be aware of some perceptions or arguments that make me think I have awareness or thinking—but in fact I am wrong, because I only think I think! This is manifestly absurd and self-contradictory.
In the case of other people, or certain animals, we assume they have conscious self-awareness because of their similarity to us. This is an argument by analogy which (even though it is very reasonable) could potentially be mistaken. But in the case of our own conscious self-awareness, there can be no doubt. This consciousness includes specific qualia or experiences such as blueness or sounds, as well as many other things.
Now this is a very interesting fact, primarily because, as far as I can see, there is no way you could possibly logically deduce it even if you knew all the Laws of Physics, and everything about Neurology which one could possibly learn from external observation alone. It is quite inexplicable, if all you know are the physical Laws of Nature, why some of those physical systems should have the additional property of having subjective experiences. Physicists mostly don't think about this issue since it's not our specialty, but when asked most of us would probably admit that there's a deep mystery here. This mystery is known in Philosophy circles as the “hard problem of consciousness” (a term coined by David Chalmers).
Please don't think I'm saying more than I am. I'm not talking about the question of why our material brains are arranged in the complex pattern that they are, as one might in an Argument from Design. Presumably Darwinian evolution is at least a large part of the answer to that question. I am asking why, once they are arranged into these patterns, they experience self-awareness.
Nor does this argument imply that there has to exist a detachable “soul”, which is separate from our bodies, and survives death. I'm not denying that the brain has a lot to do with our minds, or even that the brain and mind are in one-to-one correspondence (or more likely, many-to-one). I am only saying that we could not possibly deduce this correspondence from the Laws of Physics plus Logic alone. It might even be metaphysically necessary that living brains (and maybe artificial intelligences if we ever make them) have minds. But if so, we've just learned something about Metaphysics!
That Consciousness tells a story against Naturalism can be seen by the great efforts which many Naturalists take to resist the unavoidable conclusion. The first main counterattack is to try to deny the existence of the problem at all, through some type of “eliminative” or “reductionist” materialism. Maybe Consciousness is just another name for certain kinds of information processing which happen to occur in the brain. As in the Sondheim musical: “The woods are just trees, the trees are just wood!”
As much as I respect philosophers like Daniel Dennett for trying to make this idea precise, I just don't think it can work. Self-awareness might well turn out to be related to certain types of causal events in the brain, but we knew that we were self-aware long before we knew anything about neuroscience. So we cannot say that self-awareness is by definition a certain pattern of neurons. If folks like Dennett are right that there's no hard problem to explain, then their position has to be true by logical necessity. And it just isn't, because no matter what you tell me about the physics, I could assert without contradiction that nothing in it is self-aware.
The second main counterattack is to say: “We may not know the answer now, but Science will discover it one day! Once upon a time, some people used to think that biological life was due to some inexplicable élan vital, but now we know that it can be explained entirely through ordinary chemical processes. The same will one day be true of Consciousness.”
It's a little presumptuous to appeal to future scientific discoveries as an argument for any position, since by definition those discoveries haven't happened yet. That is why these people instead make an inductive argument, based on imagined triumphs of Science over Mysticism in the past.
But there is a key dis-analogy between Life and Consciousness: we are directly aware of the latter but not of the former (except insofar as it includes the latter). And the argument that Physics cannot explain Consciousness is not based on the detailed form of the Laws of Physics. So long as they consist of formal mathematical equations which merely describe the spatio-temporal patterns of material entities, it seems that the problem remains insoluble. At the very least, a radical change in how we even do Physics would be necessary. And as for neurological studies, surely brain researchers could go on and on making lists of which neural processes correspond to which conscious sensations, and classifying them into patterns, without ever explaining from the basic Laws of Physics why that particular set of correspondences should hold (or any set).
I said earlier that I am going to confine myself to plausibility arguments, but in this stage of the argument I think strict demonstration is possible: to deny that we are conscious clearly contradicts experience; but to say that our consciousness follows logically from the known Laws of Physics is also manifestly false when consciousness is properly defined. So it appears that our description of the Universe in terms of physical laws is incomplete.
This is why many of the early Enlightenment philosophers and scientists were Dualists. Because they assigned all conscious, sensory, and “secondary” qualities to mind rather than matter, they were free to construct scientific descriptions of matter which made reference only to their “primary” qualities, those capable of mathematical modeling. Having assigned these quantities to the “soul”, they were free to do quantitative physics on the rest. To go one step further and also banish these secondary qualities from the mind, was for them obviously inconsistent. As the philosopher St. Ed Feser says:
...the reductive method in question is like the method of getting rid of all the dirt in the house by sweeping it under a certain rug. While this is a very effective way of getting rid of the dirt everywhere else, it is not a strategy that could possibly be used to get rid of the dirt under the rug itself. On the contrary, it only makes the problem of getting rid of that dirt even worse. And that is exactly why the mind-body problem as it is understood today essentially came into existence with Galileo, Descartes, and Co. and has remained unsolved to the present day. What these early modern thinkers wanted (for certain practical and political ends) was a completely quantitative, mathematical description of the world. Irreducibly qualitative features—secondary qualities, final causes, and the like—since they would not fit this model, were thus essentially defined away as mere projections, “swept under the rug” of the mind as it were. But that only makes the idea of dealing with the mind itself in the same manner even more hopeless. For these early moderns, the mind just is, you might say, the holding tank for everything that doesn’t fit their quantitative method. Naturally, then, that method cannot coherently be applied to the mind itself.
This does not mean that a Cartesian mind-body Dualism is the only or best way of describing our situation—I think it isn't—but at least it recognizes explicitly some of the problems at stake. (There are several other options which recognize the objective reality of the mind, which go by names such as “Property Dualism”, “Hylomorphic Dualism”, “Epiphenomenalism”, “Idealism”, etc.) But any view which says that all mental quantities can in principle be derived from a purely physical description of the brain, is necessarily incoherent and wrong on philosophical grounds. And no amount of progress in empirical Science can ever prove that which is logically impossible.
Note that the logical contradiction lies in a reductionistic form of materialism which claims that all of our mental properties can be derived from external, physically measurable properties. On a non-reductionistic definition of "matter", to mean "that mysterious thing which we are made of, which may have additional properties besides those which can be externally measured", it would not necessarily be a contradiction to say that we are entirely made out of matter. Such a viewpoint would be a type of Property Dualism, which asserts that that we are one type of entity which has both physical and mental properties.
My arguments should stand on their own apart from any suspicions about my motivations. But since this term “soul” has popped up, let me add that for many years, I thought it was possible to reconcile Christian theology with the view that the human mind is identical to the material brain. I thought then, and I still think now, that the reason we will live forever is because of God's promises and his faithfulness, and not because of what we are “made out of”. It was not my interest in Theology, but trying to make sense out of the Philosophy of Mind, which led me to see the contradiction in a purely materialistic conception of human beings: that we are solely what can be physically measured about the brain.
Next: Stories and Atoms
[Next-to-last paragraph added later.]