If naturalism is true, human cognitive faculties were produced by unguided evolution for survival, not truth-tracking. Plantinga's EAAN: we have no reason to trust faculties shaped by a process that had no interest in truth — including the faculties that concluded naturalism is true. Naturalism is self-defeating. Christianity grounds rational reliability in a rational Creator.
Key claims
—J.B.S. Haldane (atheist biologist, 1927): "If my mental processes are determined wholly by atoms, I have no reason to suppose my beliefs are true"
—Plantinga's EAAN: P(R|N&E) is low — probability that our cognitive faculties are reliable, given naturalism and evolution, is low or inscrutable
—Patricia Churchland (secular philosopher): "Truth, whatever that is, definitely takes the hindmost" on naturalism
—If we have a defeater for cognitive reliability, we have a defeater for every belief — including the belief in naturalism
—Christianity grounds reliable cognition: human minds made in the image of a rational God designed for truth-tracking
The argument in Section 04 addresses morality. There is a structurally similar but logically independent argument about rationality itself: if atheistic naturalism is true, human beings have no warrant for trusting their own cognitive faculties — including the faculties by which they concluded that naturalism is true. Naturalism is therefore self-defeating.
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The argument from reason stated precisely
C.S. Lewis first articulated this argument in Miracles (1947), in the chapter titled "The Cardinal Difficulty of Naturalism." Victor Reppert subsequently formalized it, and Alvin Plantinga developed the most rigorous version as the Evolutionary Argument Against Naturalism (EAAN). All three versions converge on the same point.
The argument proceeds as follows:
The Argument from Reason (Reppert's formalization)
P1No belief is rationally inferred if it can be fully explained by non-rational causes.
P2If naturalism is true, all beliefs — including the belief that naturalism is true — can be fully explained by non-rational causes (neural processes shaped by natural selection for survival).
P3Therefore, if naturalism is true, no belief is rationally inferred.
∴If no belief is rationally inferred on naturalism, then the belief that naturalism is true is not rationally inferred. Naturalism therefore cannot be rationally believed.
The key move is the second premise. On naturalism, human cognitive faculties are the product of unguided evolution operating through random mutation and natural selection. Natural selection selects for what enhances survival and reproduction — not for what produces true beliefs. A belief that is false but adaptive would be selected with exactly the same efficiency as a belief that is true and adaptive. In fact, many false beliefs might be more adaptive than true ones: the belief that one's tribe is superior might enhance cohesion and fighting capacity; the belief that one's actions are divinely sanctioned might produce confidence under pressure.
J.B.S. Haldane — a biologist and committed atheist, not a theologian — acknowledged the problem as early as 1927:
If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true... and hence I have no reason for supposing my brain to be composed of atoms.
Haldane's point is precise: if the content of belief is entirely determined by physical processes, then the truth-value of that content is irrelevant to whether the belief is held. The belief is held because of its physical causes, not because it tracks reality. A brain that systematically produces false beliefs but survives and reproduces thereby has exactly the same natural selection fitness as a brain that produces true beliefs. Therefore, on naturalism, we have no reason to suppose our beliefs — including our belief in naturalism — are true.
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Plantinga's Evolutionary Argument Against Naturalism
Alvin Plantinga, Distinguished Professor of Philosophy at Notre Dame, developed this argument into its most rigorous form in Warrant and Proper Function (1993) and Where the Conflict Really Lies (2011). The argument, called the Evolutionary Argument Against Naturalism (EAAN), has been the subject of enormous philosophical debate and has been acknowledged as a genuine philosophical challenge even by atheist critics.
The formal structure:
Let R = the reliability of human cognitive faculties (their tendency to produce true beliefs). Let N = naturalism. Let E = the thesis that human cognitive faculties were produced by unguided evolutionary processes.
Plantinga argues that P(R|N&E) — the probability that our cognitive faculties are reliable, given that naturalism and evolution are both true — is either low or inscrutable. Here is why:
On naturalism and evolution, the only thing that matters for survival is adaptive behavior — behavior that enhances reproductive fitness. Adaptive behavior can be produced by reliable beliefs (beliefs that track reality) or by unreliable beliefs (beliefs that don't track reality but happen to produce adaptive behavior). There is no selection pressure for truth per se — only for adaptive behavior. Therefore, given N and E, there is no reason to expect our beliefs to track reality. P(R|N&E) is low or inscrutable.
But if P(R|N&E) is low, then the naturalist has a "defeater" for R — a reason to doubt that his cognitive faculties are reliable. And if he has a defeater for R, he has a defeater for any belief produced by those faculties — including the belief that N and E are true. Therefore, the naturalist who accepts evolution has a self-defeating view.
The conclusion to be drawn is that the conjunction of naturalism with evolutionary theory is self-defeating: it provides its own defeater. This is the real conflict in our culture — not between science and religion but between naturalism and science. Naturalism is at war with science, not Christianity. Christianity, in fact, is what makes science possible by providing the metaphysical foundation for a rational, ordered universe and reliable human minds capable of understanding it.
Patricia Churchland, a secular philosopher of neuroscience at UC San Diego, made essentially the same concession from the other side:
Boiled down to essentials, a nervous system enables the organism to succeed in the four F's: feeding, fleeing, fighting, and reproducing. The principal chore of nervous systems is to get the body parts where they should be in order that the organism may survive. Improvements in sensorimotor control confer an evolutionary advantage: a fancier style of representing is advantageous so long as it is geared to the organism's way of life and enhances the organism's chances of survival. Truth, whatever that is, definitely takes the hindmost.
"Truth, whatever that is, definitely takes the hindmost." This is a secular neurophilosopher acknowledging that, on a purely naturalistic account of cognition, truth-tracking is not what the brain is for. It is for survival. The atheist who trusts the conclusions of his own reasoning about God's existence is, on this account, trusting faculties that were not designed for that purpose and have no reason to be reliable in that domain.
Christianity resolves this problem directly. If human beings were created by a rational God who made them in his image — with cognitive faculties designed for the purpose of understanding reality — then we have every reason to trust those faculties as truth-trackers. The reliability of human reason is exactly what you expect on Christian theism. It is exactly what you cannot guarantee on naturalism.