Naturalism is the view that all of life, indeed everything that exists, can be explained by physical and chemical causes. Such a view also results in every event being caused by a prior physical and chemical cause, to the extent that the universe is causally closed, which means that there are no new causes arising that are not caused themselves. Thus in naturalism, human agency is denied, and no human can originate any action or thought. Naturalists therefore hold that all human action is determined, we cannot but help believe, think, emote, and like what we like, for all our thoughts, emotions, and deeds are determined by prior causes.
Non-philosophical naturalists, such as some in the physical sciences, have not thought through the implications of this. With one breath they will hold to pure naturalism, then with another try to maintain that we can make moral choices and have free will. Naturalists who have thought through the philosophical consequences to their belief system will deny free will and moral responsibility.
Theists in general, and Christians in particular, by contrast hold that there are causes in the universe that are not derived from physics and chemistry, but can be attributed to human souls and to God. If we can demonstrate that naturalism is false, then non-naturalism must be true, and the Christian position is supported.
Enter the argument from reason. To the naturalist, all thought is brain function, and all brain function is ultimately reduced to predetermined chemistry. The problem with this is that if our thoughts are all the result of natural forces, then reason is either entirely illusion, or is redefined to be predetermined processes. If naturalism were true, we would be no more free to reason to a different conclusion than vinegar and baking soda would have the freedom to react differently on my kitchen counter. All human reason, including perception of the world around us, would be reduced to physical forces of which we have no control.
In the excellent anthology True Reason (Gilson & Weitnauer, eds.), Lenny Esposito gives a powerful explanation and critique of naturalism. Esposito explains:
Basing our reason on a cause-and-effect model doesn’t make sense. Reason is not the kind of thing that can be explained by examining the makeup of the brain or its physical processes. Reason must be oriented toward an objective external reality and our ability to tap into that reality. If, in fact, naturalism is true, it means either that what we take to be rationality is either in no way grounded in external, objective truth (and as such cannot be called rational), or we’re fooling ourselves into thinking that rationality exists at all. (p.104-105)
Esposito supports his views by giving examples from Alvin Plantinga, C. S. Lewis, and Victor Reppert, who also hold that the argument from reason supports the existence of God. Interestingly, even atheist Thomas Nagel has pointed out the absurdity of naturalism in his book Mind and Cosmos: Why The Materialist Neo-Darwinian Conception of Nature is Almost Certainly False.
The point is that if pure cause-and-effect were true, then our thoughts are not derived from observing the universe and drawing rational conclusions, but are rather caused by predetermined chemistry in our brains. Plantinga goes so far as to say that if naturalism were true, all our cognitive faculties cannot be trusted, for they need not accurately represent the way the world actually is. If a rabbit runs from all lions not because they might be eaten, but because they happen to have a brain chemistry that makes them think the lion is playing a fun game of tag, the effect is the same. Under naturalism, our reason cannot be trusted.
Thus the irony is astounding. The naturalist, who typically wraps himself in the cloak of reason and rationality in denying that the human soul can originate thoughts, ends up pulling the own foundation out from under himself, collapsing into a pile of self-refuting, unfounded beliefs. Many of the greatest philosophers have realized this, with even men like Kant having to posit God to save the rationality of his system. I wonder how many modern thinkers irrationally cling to an illogical naturalism mainly so they will not have to admit that God exists.
Oh, that they would merely read their Bibles and walk into the loving arms of the true God, accept that they are a special creation that has a will, and can freely choose to accept God’s mercies.