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"Christianity is evidentially challenged." Jim looked at me evenly as he spoke. We were eating lunch at a local Indian restaurant where we frequently met to discuss my Christian faith and his atheism. Jim had been a Christian in the past, but had since become inclined toward naturalism, including a naturalistic view of human beings. On this particular day, he told me some of the reasons why he thought Christianity lacked evidential support. One reason stood out: according to Jim, the human mind was a purely physical entity, a fact that he said fit beautifully with naturalism but poorly with Christianity's traditional account of the soul.
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Jim is not alone. Distinguished thinkers like Alex Rosenberg and Jaegwon Kim champion a naturalistic view of the mind in everything from popular titles like The Atheist's Guide to Reality to technical works like Physicalism, or Something Near Enough.
"So, you think the mind is a purely physical thing?" I asked.
"Yes I do."
"I see. Tell me what you mean."
Jim explained a perspective that we might call "robust physicalism." It actually comprises a range of theories, including eliminative materialism, reductive physicalism, and others. These theories typically hold in common that the mind is just the brain (or is entirely reducible to the brain). A person's feelings, thoughts, and desires are, at bottom, just various physical-chemical states of grey matter spurred on by an array of neurotransmitters. Give me that ole-time oxytocin!
The brain, of course, is a purely physical thing; it has only physical attributes like shape, mass, and size. In fact, the brain is nothing more than a "meat computer"—a super iPad, as it were, only made out of flesh, fat, and blood vessels instead of metal, plastic, and silicon. Needless to say, on this view, a soul is hard to come by.
Jim, along with a number of other thinkers, sees this view as the most straightforward application of naturalism to the mind. If fundamental reality is physical, then it makes sense that every derivative entity would be physical or ultimately reducible to the physical. The view has a nice elegance to it: nature in, nature out.
Robust Physicalism Undone?
Despite robust physicalism's elegance, the view suffers from at least one mild disadvantage: it destroys itself. If robust physicalism is true, then a person's mind is nothing more than (or is completely reducible to) his brain and its physical-chemical interactions. As a result, all of his "beliefs" and "thoughts" are physical things and processes. But physical things and processes, like electrons and protons, don't "think" or "reason," they just mindlessly interact. This implies that people don't actually think or reason about anything; "thinking" is just a brute physical-chemical incident in the brain. But if there's no such thing as thinking of any kind, it's very difficult to see how there could be good thinking, including good reasoning. And without good reasoning, there can't be good reasoning that supports robust physicalism.
Thus, having substituted matter for mind, physicalists are literally left with no justification for their own theory. By destroying reason, physicalism has destroyed itself.
For these and other reasons, some naturalists have pivoted to a more moderate version of naturalism and the mind. Moderate physicalist perspectives are legion, but the current favorite flavor is "emergence." On this view, the mind emerges from the physical complexity of the brain. As with robust physicalism, the brain itself is purely physical. Yet the stunning intricacy of the physical brain gives rise to more than just physical characteristics. In addition to having size, mass, shape, and the like, the brain produces novel, non-physical attributes like consciousness, will, desire, and so on. Just as fire emits smoke, so the brain emits the mind.
A frequent illustration of emergent complexity involves water, H2O. When oxygen and hydrogen combine under specific conditions, a novel attribute arises—liquidity. This attribute is qualitatively different from any of the properties of oxygen and hydrogen individually. Similarly, when the physical matter that comprises a brain is organized in the right way, novel attributes of consciousness, will, and so on spontaneously pop into being.
Crucially, "mind" is incapable of existing on its own, apart from the brain. There's just the brain and its two types of properties. The existence of non-physical characteristics radically depends on the physical brain. If the brain were destroyed, then consciousness, will, desire, and the like would disappear. Similarly, if one were to throw water on a fire, its smoke would vanish.
Emergence of Zilch
Emergence, however, suffers the same fate as robust physicalism: in the end, it is self-defeating. To see why, consider the H20 analogy. What advocates of this view fail to recognize is that the novel property of liquidity is completely determined by the combined physical characteristics of hydrogen and oxygen. Even though liquidity is a new kind of thing, every part of its existence and behavior is directly controlled by its constituent elements. Similarly, a fire gives rise to smoke, and any changes to the fire will directly determine changes in the smoke. If one adds gasoline, the smoke will change. If one opts instead for the collected works of Richard Dawkins, the smoke will change again.
The upshot is that, even if the physical complexity of the human brain gives rise to "novel" characteristics like consciousness, volition, and so on, every part of the existence and behavior of these characteristics is directly controlled by the physical brain. And the brain—as a physical entity—is ultimately governed by the laws of physics and chemistry, just as in robust physicalism. In the final analysis, purely physical causes and effects run the show; reasoning, thoughts, and decisions are mere bubbles floating on the surface of an ocean of materialism.
This all means one thing: the same problem that undercuts robust physicalism also undercuts emergence theory. Reasoning, evidence, and arguments don't do any real work. They appear to make a difference, but they do nothing of the sort. What really determines people's thoughts and conclusions are physical-chemical reactions in the brain. Just as with robust physicalism, this result directly implies that no one can ultimately believe emergentism on the basis of good evidence or arguments. Reason has again been replaced by chemistry.
Like other thinkers, my colleague Jim embraces naturalism over Christianity. He says that naturalism—and its view of human beings—is evidentially superior. It has better evidence, better arguments, and better reasons. Christianity doesn't measure up to the same high standards of reason, evidence, and argument. It is "evidentially challenged."
Be that as it may (and it certainly could be contested), naturalists like Jim miss a grim irony. Taken on its own terms, Christianity at least affirms the reality of good evidence and arguments. People can think. They can reason. By contrast, naturalism destroys the very notion of meaningful evidence, arguments, reasons, and thinking. This worldview not only undercuts any evidence it may cite against Christianity, it also obliterates any positive evidence for itself. In the end, naturalism kills reason. And by killing reason, naturalism kills itself. •
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