In his book Miracles, C.S. Lewis provides a fascinating argument on how our use of reason points to the existence of the supernatural. To understand the supernatural, though, we must first define what we mean by the “natural.” According to Lewis, “The Natural is what springs up, or comes forth, or arrives, or goes on, of its own accord: the given, what is there already: the spontaneous, the unintended, the unsolicited.” The Naturalist assumes that this is all there is. However, if “any one thing exists which is of such a kind that we see in advance the impossibility of ever giving it [a naturalistic] explanation, then Naturalism would be in ruins.” According to Lewis, our use of reason is just such a thing that defies naturalistic explanation.
Reason implies inference. If we directly witness a phenomenon through our senses then we do not conclude it’s truth based upon reason but rather through our immediate observation. If however, we use our powers of inference to draw additional conclusions based upon the things that we have witnessed with our senses, then we have resorted to reason. If I conclude that the sun rose this morning because I witnessed it, I have not arrived at that conclusion through reason. However, if I infer that the sun must have risen this morning because it has risen every other morning during my lifetime, even though I have not left my house and have not personally witnessed the sun today, then I have reached my conclusion through reason.
Naturalists advance their arguments through the use of reason. They present various evidences and infer that Nature is all there is. But if Nature is “the whole show,” then everything, our reasoning abilities included, must have developed of their own accord. This begs the question of whether a naturalistic explanation for our reasoning abilities can be found.
According to natural selection, useful traits are preserved. The ability to use inference to point toward truth (as opposed to flawed inferences that point to falsehood) is useful. Therefore, people with the habit of drawing objectively truthful inferences would be at a competitive advantage and this trait would be passed on to their offspring. This is a particularly important point for naturalists. They must concede that objective truth exists in order to avoid finding themselves in an un-affirmable contradiction (by claiming the absolute truth that there is no absolute truth). Explaining how we came to develop our habits of inference is hardly reassuring if those inferences do not point to the objective truth that naturalists and super-naturalists both acknowledge exists. Thus naturalists must justify within their worldview not only that we use inference but also that our inferences are reliable.
But the statement, “inferences that point to objective truth are useful” is itself an inference. The naturalist may collect evidences of how these types of inferences have proven to be useful in the past, but the supposition that they will continue to be so and will therefore generally be preserved is an inference. How are we to know that this inference is true? Should we come to that conclusion because it is useful? That is begging the question. We can only conclude that our reasoning abilities point to ontological truth by using our reasoning abilities. That is circular reasoning. After all, if our reasoning abilities actually pointed to falsehood, we may be absolutely convinced that they point to ontological truth but we would be unfortunately mistaken. Unless we first presuppose the value of our reasoning we can never prove that we have the ability to know ontological truth. All truth ends up being unknowable. This brings the naturalist back to the same problem of un-affirmability, being forced into the position of “knowing” that all truth is unknowable.
Naturalists may respond that they are willing to presuppose the value of reason. But this is precisely what they must not do if they are to be consistent with their worldview. Their basic premise is that all things can be explained by naturalistic means. But by presupposing reason, they are now claiming that all things other than reason itself can be explained by naturalistic means. If we grant any exception then there must be at least one thing outside the natural. Therefore, our ability to reason through inference shows that at least for this one thing, the supernatural must exist.