Here's a debate on whether anything supernatural exists where I argued the Pro case. I attempted to defend the argument from reason and a version of Plantinga's evolutionary argument against naturalism. Fun times.
http://www.debate.org/debates/The-supernatural-exists./1/
Here's my opening statement:
Good evening, and thank you for coming to tonight's debate.
My opponent stipulates that I may defend any version of the supernatural I wish, so let me define the version of supernatural I intend to defend in this debate.
The supernatural refers to one of two things: (1) to anything that exists that is not describable by the laws of physics and chemistry, and (2) any event in the natural world whose cause is not also part of the natural world. By "the natural world," I mean the world of matter and energy, or that aspect of reality that is describable by the laws of physics and chemistry.
What I will argue is that rationality and justified true beliefs are not possible if all that exists is the natural. Naturalism (the view that only the natural exists) is self-refuting because it undermines the necessary preconditions for rational thought and justified belief, including whatever line of reasoning lead to belief in naturalism. If we are in fact rational and justified in at least some of our beliefs, then some version of supernaturalism must be true.
If naturalism is true, then all of our beliefs are determined by non-rational cause and effect. After all, the brain is just a physical object that obeys the laws of nature. For whatever belief one has, it doesn't matter whether there are good reasons for it. So long as the brain fizzes in the right way, that belief will emerge. A belief can only be rational or justified if it is the result of good grounds. But arriving at a belief through physical causes is quite different than arriving at a belief through a line of reasoning and "seeing" the logical relations between propositions. In fact, we frequently dismiss the validity of a belief by pointing to its causes. For example, people frequently say things like, "You only believe that because you were born in a western culture." A belief that is caused by an accident of birth is said to be unjustified on that basis. If the fact that a belief is caused is any reason to dismiss it as being justified or rational, then given naturalism, none of our beliefs are justified or rational, including the belief in naturalism because they are all caused by our brain chemistry. The perception we all have of thinking through a line of reasoning is just an illusion since each step in the process is directly caused by the underlying chemical activity in our brains which happens deterministically according to the laws of nature.
One might respond by saying the brain acquired the ability to produce mostly true belief through evolution since true beliefs are more advantageous than false beliefs. So even though our beliefs are caused by blind mechanistic events in the brain, as long as the brain is "programmed" through evolution to result in mostly true beliefs, the fact that our beliefs are caused by brain chemistry doesn't undermine the reliability of our belief-producing cognitive faculties. Our beliefs may not be "rational" in the sense of being arrived at through a process of sound reasoning, but they can nevertheless be reliable.
However, natural selection can only act on behavior. What determines whether you survive and reproduce in any situation is the movement of your body parts, not whatever belief or desire that might be going on in your head. The only way belief and desire could contribute to survival value is if belief and desire determined your behavior. Under naturalism, it isn't possible for your beliefs and desires to affect your behavior. Your behavior is determined by your brain chemistry. The brain fizzes in a certain way, and that fizzing produces electrical signals that are sent to your muscles via your nervous system. Since there is no soul under naturalism, all of your mental events are caused by the brain. The mental events themselves don't cause anything. Each brain state, from moment to moment, is caused by the previous brain state according to the laws of nature. There is no room from anything like a desire or a belief to have any causal influence over the brain. The desire and belief are, themselves, caused by the brain. They are passive and just ride on top of brain activity. The feeling we have of intending to act, then acting on that intention, is just an illusion created by the brain. One and the same brain state might simultaneously cause the sensation of desire and the movement of the arm, but the desire does not cause the arm to move. Since natural selection selects for adaptive behavior wholly apart from whatever belief/desire might be associated with that same brain state, natural selection cannot select for true beliefs or reliable belief-producing cognitive faculties. So if naturalism is true, we should not expect to have developed the capacity for arriving at true beliefs. That makes naturalism self-refuting.
But let's suppose that somehow or other beliefs and desires actually DO affect our behavior. Under naturalism, they can only do so by virtue of their underlying physical brain state. That is, it would not be the semantic content of our desires and beliefs that result in behavior; rather, it would be the syntatic content of the underlying brain state. So we'd be in exactly the same situation. If syntax determines our behavior, then it doesn't matter what the semantic content is. If a false belief has just the right syntax to get our bodies moving in such a way as to ensure our survival and reproduction, then false beliefs would be just as adaptive as true beliefs. If it happened that true beliefs resulted in adaptive behavior, that would just be dumb luck. It would be a remarkable coincidence if it happened that mostly true beliefs were associated with syntax that lead to adaptive behavior.
But let's suppose that somehow or other, even under naturalism, that even the semantic content of our desires and belief affect our behavior. It's hard to imagine how that could even be possible under naturalism, but let's suspend belief for a moment and pretend that it's not only possible, but actual. In this case, one might argue that since true beliefs are generally more advantageous that false beliefs, that evolution would tend to result in reliable belief-producing cognitive faculties. The problem, though, is that for any true belief one might think is adaptive, it's trivially easy to think of a false belief that would do the same thing. For example, one might think that if one has a true belief that snakes are poisonous and ought to be avoided, that will result in a person living longer than somebody who thought snakes were safe and frequently stuck their hands down in rattle snake nests. But it is just as easy to imagine a person who wrongly thinks rattle snake are safe and fun to play with and that the best way to play with them is to run away from them. Running away, rather than sticking their hand in the nest, would ensure the person's survival. Or, you can imagine a person has an innate desire to die by poisoning, and he wrongly and stubbornly believes that fresh fruit and vegetables are the best poinsons by which to commit suicide. That would result in a person eating healthy and living longer. Since it's just as easy for a false belief to result in adaptive behavior as a true belief, there is no reason to think that evolution would produce reliable belief-producing cognitive faculties given naturalism.
So naturalism is self-refuting. If naturalism were true, we should not expect that any of our beliefs would be true or that we'd have reliable belief-producing cognitive faculties. And with that being the case, belief in naturalism is irrational. However, if we are quite convinced that we are rational beings and that we do generally have true beliefs rather than false beliefs, then to be consistent, we must reject naturalism. Rejecting naturalism--that the natural world is all their is--entails embracing supernaturalism--that some things exist beyond the natural.
Therefore, supernaturlism is true.
