The argument from reason is an attempt to demonstrate that belief in naturalism is unjustified; that is, it is a belief that cannot be trusted. This is done by showing that belief in naturalism is contradictory to confidence in human reason. This is an important point, as atheists often attempt to frame their worldview as “more reasonable” than one that holds to transcendent ideas. A general statement of the argument from reason would be as follows:
Either “reason” is merely an illusion of physics—in which case there is no justification for relying on it to produce truthful beliefs—or “reason” is something more than physical—in which case naturalism is false. If human reason is driven by mindless particle interactions, it does not necessarily correspond to truth. If we believe reason corresponds to truth, we cannot also believe reason is determined purely by physical means.
An even more concise phrasing would be “the existence of reason itself argues against naturalism.”
As with any discussion of philosophical ideas, specific definitions matter. In this case, reason is the ability of a mind to infer and conclude in a logical way. As it applies to the argument from reason, reason refers to the use of the intellect to come to real, true conclusions. Naturalism is the belief that everything is reducible to physical components; it is the view that reality is nothing more than matter and energy.
Philosophy also draws a distinction between the questions “how do we know truth?” and “what is reality?” These fields are known, respectively, as epistemology and metaphysics. The argument from reason is an epistemological claim: it narrowly examines how we know and how much we trust an idea.
Because reason is an inextricable part of our understanding, the argument from reason heavily implies a metaphysical claim, as well. If “reason” is objectively valid—if reason is “real”—then naturalism would have to be “unreal.” If reason does not exist, why did humanity come to see it as we do: as a non-material, but real thing? If there were no such thing as light, we’d never know we were living in darkness; in fact, such an idea would be pointless to consider. Yet we distinguish between reason and irrationality.
The argument from reason is really a series of arguments, in different forms, voiced by both believers and non-believers. Thinkers such as Victor Reppert, C. S. Lewis, G. K. Chesterton, and Thomas Nagel have been associated with these claims. Each argument has its own strengths and weaknesses, but they all share a common theme. To suggest that literally everything about the universe is effectively random is to suggest that one’s own thoughts and conclusions are equally unreliable. One does not have to start from—or even conclude with—a biblical worldview to appreciate the logical force of this idea.
An especially famous version of the argument from reason was popularized by Alvin Plantinga: the evolutionary argument against naturalism (EAAN). Plantinga notes that evolution is driven by survival of the “fittest,” yet beliefs more “fit” for survival are not necessarily the same as those that are “true.” Therefore, if evolution is true, belief in naturalism is unjustified. In other words, at the very least, belief in naturalism logically contradicts itself, thanks to evolution.
To visualize the evolutionary argument against naturalism, consider an extreme example: a man develops the overwhelming desire to be eaten by an invisible bear. This drives him to seek out locations where he sees no bears. That belief is contrary to survival—not to mention bizarre—but more importantly, it’s factually wrong. His reasoning did not lead to truth, since there are no invisible bears. And yet, that bizarre, false reasoning makes the man more “fit” for survival since it encourages him to stay away from the bears he can see; that is, ones that exist.
This demonstrates how “that which is good for survival” is not identical to “that which is true.” It is entirely possible for human reasoning to be farcically wrong and still provide “advantageous” results from a survival or evolutionary perspective. If human reason is entirely the result of purposeless, survival-driven evolution, then “useful” reasoning and “truthful” reasoning are distinct categories. That implies all products of human reason are untrustworthy, including belief in naturalism and evolution.
This comes back to the core assertion of the argument from reason: one can believe in naturalism or trust in reason, but one cannot do both. The conflict might seem petty when applied to practical matters, but the more esoteric the idea is—as would be the case with concepts like naturalism—the less confident one could be in the truth-correspondence of human reason.
The most common attempt to refute arguments from reason uses the concept of emergence. This is the claim that certain concepts develop out of—they “emerge from”—the combined interaction of less complex things. Of course, in a naturalistic worldview, emergent is synonymous with very complicated. Either the entire process ultimately rests on simple physics, or it doesn’t. If the process doesn’t boil down to matter and energy, then it’s not naturalistic. Another frequent error is to claim that debunking a single version of the argument from reason somehow proves naturalism. This is, ironically, irrational, since demonstrating that a conclusion was arrived at illogically does not, itself, mean the conclusion is false.
As with most such ideas, the argument from reason has limitations. Its purpose is to suggest an irreconcilable contradiction between the statements “I believe naturalism is true” and “I trust in human reason.” In and of itself, these arguments say nothing about the existence of any particular deity. Nor do they suggest much about the nature of God or the Bible. That said, the argument from reason is a useful tool that demonstrates how those who reject God—as do naturalists—are ultimately dealing in illogic and stubbornness (Romans 1:18–25; Jude 1:10).