Can Naturalism Account for Reason?

Can Naturalism Account for Reason?

Human thought is produced through the brain—but is it also guided by truth, logic, and evidence? The argument from reason asks whether naturalism can explain not merely how beliefs occur, but why any of them should be trusted.

Introduction

Every worldview is examined through reason.

We compare evidence, recognize contradictions, draw conclusions, and revise our beliefs when the argument demands it. Naturalism itself is ordinarily defended through rational reflection: its advocates appeal to science, explanatory simplicity, and the apparent success of physical explanations.

This creates a searching question.

Can naturalism explain the very reasoning by which naturalism is affirmed?

The argument from reason does not deny that thought involves the brain. Nor does it claim that evolution necessarily produces unreliable minds. Accurate perception frequently contributes to survival, and no serious argument should pretend otherwise.

The deeper issue concerns the difference between a belief being physically caused and a belief being rationally justified.

A brain event may explain why a thought occurred. It does not automatically explain why the thought is true, why its conclusion follows from its premises, or why a person ought to accept it. The challenge for naturalism is therefore not merely to describe the machinery of thought, but to account for truth, meaning, logical obligation, and the reliability of human reasoning within a world understood as fundamentally nonrational.

Darwin's Own Doubt

It is worth noticing at the outset that this worry did not begin with Christian apologists. It occurred to Charles Darwin.

In a letter to the philosopher William Graham on 3 July 1881, near the end of his life, Darwin confessed a lingering unease. He agreed with Graham that the universe did not seem to be the mere result of chance. Yet he immediately added that a "horrid doubt" always arose in him: whether the convictions of a mind developed from lower animals could be trusted at all. He wondered whether anyone would place confidence in the convictions of a monkey's mind, supposing such a mind had any convictions.

Darwin never resolved the doubt, and he did not treat it as a refutation of his own theory. But he saw the problem clearly. If the human mind is simply the outcome of a long, undirected biological process aimed at survival rather than truth, what warrant do we have for trusting its most ambitious conclusions—including grand theories about the origin of mind itself?

The argument from reason is, in large part, an attempt to take Darwin's doubt seriously and to ask which picture of reality best answers it.

What Is Naturalism?

The word naturalism is used in several ways.

Methodological naturalism is a rule of scientific investigation: when studying physical phenomena, scientists search for regular natural causes rather than appealing prematurely to miracles. Christians can ordinarily accept this method without believing that nature is all that exists.

Metaphysical naturalism is a much broader claim. It maintains that the natural world is the whole of reality. There is no divine mind behind the universe, no immaterial soul, and no transcendent source of rational order. Many contemporary naturalists are physicalists, holding that everything that exists is ultimately physical or wholly dependent upon the physical. Philosophers disagree, however, about exactly how naturalism and physicalism should be defined.

The argument from reason is directed primarily against forms of naturalism in which every human thought is completely accounted for by physical processes operating according to nonrational laws.

Calling physical laws nonrational does not mean that they are irrational or disorderly. Gravity does not make logical mistakes. It simply does not reason. Electrons do not examine evidence, neurons do not recognize the validity of a syllogism, and chemical reactions do not believe conclusions because those conclusions follow from premises.

Yet human beings appear to do precisely these things.

Causes and Grounds Are Not the Same

Suppose a man believes that his house is on fire.

There could be many causes of that belief. He may see smoke through the doorway. Someone may shout a warning. A hallucination, fever, electrical stimulation, or blow to the head might also produce the same conviction.

In each case, the belief has been caused. But it has not been justified in each case.

Seeing smoke, feeling intense heat, and hearing the fire alarm provide grounds for the belief. A hallucination may explain why the man believes there is a fire, but it does not give him a good reason to believe it.

The distinction becomes even clearer in formal reasoning:

1. All human beings are mortal.
2. Socrates is a human being.
3. Therefore, Socrates is mortal.

The conclusion is not merely the next event in a physical sequence. It is supported by the premises. A person who understands the argument recognizes that, if the premises are true, the conclusion cannot be false.

This involves at least three different realities:

• The thoughts have meaning.
• The premises stand in a logical relationship to the conclusion.
• The thinker accepts the conclusion because of that relationship.

A complete account of reasoning must therefore explain more than neural activity. It must explain how the content of one belief can provide a rational ground for another.

C. S. Lewis and the Argument from Reason

C. S. Lewis developed his best-known version of the argument from reason in Miracles. The book first appeared in 1947, and Lewis substantially revised its third chapter for the 1960 edition after philosopher G. E. M. Anscombe criticized aspects of his original formulation during a February 1948 meeting of the Oxford Socratic Club. In the revision, Lewis retitled the chapter "The Cardinal Difficulty of Naturalism" and drew a careful distinction between irrational and non-rational causes that his first version had blurred.

Contrary to a popular story, there is little reason to believe that Anscombe's criticism destroyed Lewis's faith or caused him to abandon apologetics. Lewis instead clarified and reformulated the argument. Anscombe herself, revisiting the exchange decades later in a 1985 talk to the Oxford C. S. Lewis Society, judged the revised chapter a genuine improvement and described Lewis's reworking as showing honesty and seriousness. The episode is better read as a model of honest philosophical correction than as a defeat.

Lewis distinguished two kinds of connection.

The first is a cause-and-effect relationship. One physical event produces another: pressure on a switch causes a light to turn on.

The second is a ground-and-consequent relationship. One proposition provides evidence for another: dark clouds give us reason to expect rain.

A reasoning process may involve both. Neural events occur in the brain, but the thinker also understands one proposition as supporting another.

Lewis's concern was not simply that reasoning has physical causes. His mature argument is better understood as asking whether rational relations can have any genuine explanatory role if physical causes provide a complete and exclusive account of every thought.

Suppose a person concludes that naturalism is true after studying philosophy and science. If the conclusion occurred solely because prior physical events necessitated a particular neural state, what role was played by the truth of the evidence or the validity of the inference?

The naturalist may answer that the physical process and the rational process are two descriptions of the same event. Lewis's challenge is that this answer must be explained rather than assumed. How can a sequence governed entirely by physical causation also be governed by logical relations such as implication, contradiction, evidence, and probability?

The argument does not prove that neurological processes are absent from reasoning. It asks whether neurological description alone can preserve reasoning as reasoning.

Victor Reppert's Development of the Argument

Philosopher Victor Reppert has developed Lewis's argument into a broader family of challenges. His case does not depend upon one simple claim that physical causes make rational thought impossible. Instead, it asks whether a naturalistic account can accommodate several features of reason simultaneously.

Among them are:

Intentionality. Thoughts are about things. A thought may be about Jerusalem, the number seven, tomorrow's weather, or an event that never occurred. Physical objects have locations, weights, and electrical properties, but it is difficult to see how matter considered only as matter becomes about something.

Truth and falsehood. Brain states exist or do not exist, but beliefs can also be true or false. The chemical composition of a sentence does not determine whether the sentence accurately describes reality.

Logical normativity. Logic does not merely describe how human beings happen to think. It distinguishes how we ought to reason from how we sometimes do reason. Contradictory beliefs should not both be affirmed. Evidence should be proportioned to conclusions. Fallacies should be rejected even when they are psychologically persuasive.

Mental causation. When someone changes his mind because he recognizes a contradiction, the content of the contradiction appears to influence what he believes. A satisfactory theory must explain how reasons, as reasons, can participate in the production of belief and action.

Rational responsibility. We praise people who follow evidence honestly and criticize those who ignore inconvenient facts. Such judgments assume that reasoning is not merely something that happens inside us but something for which we bear some responsibility.

Naturalistic philosophers have proposed accounts of each of these features. The argument from reason should therefore not be presented as though naturalists have never considered them. The question is whether the proposed explanations collectively succeed without quietly reintroducing realities—truth, purpose, normativity, or irreducible mental content—that sit uneasily within a strictly physical account of the world.

Alvin Plantinga and Evolutionary Naturalism

Alvin Plantinga's evolutionary argument against naturalism is related to Lewis's argument, but it is not identical to it.

Lewis and Reppert concentrate primarily on whether naturalism can explain rational inference. Plantinga asks whether someone who accepts both naturalism and evolution possesses adequate grounds for trusting human cognitive faculties.

Plantinga represents the argument through three propositions:

• N: Naturalism is true.
• E: Human cognitive faculties arose through evolutionary processes.
• R: Human cognitive faculties are generally reliable.

He argues that the probability of reliable cognition given the combination of naturalism and evolution—P(R | N&E)—is low or at least inscrutable. If a naturalist comes to believe that the reliability of his faculties is doubtful, Plantinga argues, he acquires a defeater for the beliefs produced by those faculties, including his belief in naturalism itself.

This argument is often stated carelessly.

Plantinga is not claiming that evolution could never produce reliable cognition. He is not denying evolutionary biology, nor is he arguing that false beliefs are always more adaptive than true ones. His argument concerns what naturalistic evolution gives us reason to expect.

Natural selection directly favors traits that contribute to survival and reproduction. In creatures capable of belief, behavior will often be influenced by beliefs and desires together. A beneficial behavior could sometimes arise from an accurate belief, but in principle it could also arise from an inaccurate belief combined with an unusual desire.

Nevertheless, the mere possibility of adaptive falsehood does not establish that evolved cognition is probably unreliable. Plantinga must show that the connection between fitness and truth is too weak to justify confidence in our faculties. It is here that much of the philosophical debate occurs.

Does Evolution Favor Survival or Truth?

The common statement that "evolution selects for survival, not truth" is partly correct but easily misunderstood.

Natural selection does not inspect propositions and reward organisms for holding philosophically accurate beliefs. It operates through differences in reproductive success.

Yet truth and survival are often connected.

An animal that accurately distinguishes predators from harmless objects has an advantage over one that does not. A creature that correctly remembers where food and water are located will often outperform one whose internal representations consistently mislead it. Accurate spatial perception, object recognition, memory, and causal expectation can contribute directly to adaptive behavior.

For this reason, it would be mistaken to argue that evolution necessarily gives us untrustworthy senses. In ordinary environments, broadly reliable perception is frequently useful.

The harder questions arise when we move beyond immediate practical cognition.

Natural selection may help explain why human beings can navigate terrain, recognize faces, avoid danger, and cooperate socially. It is less obvious that the same process guarantees reliability when contemplating modal logic, quantum theory, metaphysics, moral obligation, or the ultimate nature of reality.

Naturalists can respond that advanced reasoning developed from more basic capacities and was then refined through language, culture, education, mathematics, and science. Human beings do not depend entirely upon unaided instinct. We correct one another, build instruments, conduct repeated experiments, and develop systems designed to expose error.

This is an important reply. It demonstrates that evolutionary explanations need not treat the human mind as a finished product whose every belief was directly selected.

But it does not completely remove the philosophical question. Scientific correction still depends upon observation, memory, inference, mathematical judgment, and the ability to recognize evidence. A method can improve fallible faculties, but it cannot begin from total cognitive unreliability. Some substantial capacity for truth must already be present.

Major Naturalistic Responses

A fair assessment must consider the strongest naturalistic answers.

Rational and Physical Explanations Can Coexist

The most direct response is that rational explanation and physical explanation need not compete.

A sentence can be described as ink on paper, as a sequence of words, and as an argument. These descriptions do not cancel one another. Likewise, a thought can be described neurologically while also being evaluated rationally.

On this view, the reason a person believes a conclusion may be both that certain neurons fired and that he recognized the force of the evidence. The rational explanation operates at the personal or psychological level, while the physical explanation operates at a neurological level.

This reply has considerable force. The argument from reason fails if it assumes without justification that physical causation and rational inference are automatically incompatible.

The remaining problem is one of integration. Naturalism must explain how meaningful and normative relations emerge from, supervene upon, or are realized by physical states. Merely naming two levels of description does not show how the content of a belief becomes causally relevant.

Reliable Cognition Is Adaptive

Naturalists also argue that Plantinga understates the correlation between truth and successful behavior.

Although isolated false beliefs may occasionally be adaptive, a creature whose beliefs were systematically disconnected from its environment would have difficulty surviving. Complex and flexible behavior generally requires reasonably accurate information.

Philosophers Branden Fitelson and Elliott Sober have challenged Plantinga's probability claims, arguing that he has not established that reliable cognition is improbable given naturalism and evolution. They also question whether his proposed probability judgments are sufficient to generate the sweeping skeptical defeat he describes.

This objection exposes an important limitation. Plantinga cannot move directly from "selection rewards behavior" to "reliable belief is improbable." The relationship between belief, desire, behavior, and fitness requires a far more detailed account.

Naturalized Accounts of Mental Content

Some philosophers appeal to teleological or evolutionary theories of mental content, often called teleosemantics. The most influential versions were developed by Ruth Millikan and Fred Dretske.

These theories attempt to explain what a mental representation means by examining the function it acquired through evolution or learning. A perceptual system may represent predators because detecting predators is part of the function for which that system was selected. The possibility of malfunction then helps explain how a representation can be false.

Such theories represent serious efforts to explain intentionality and error within a naturalistic framework.

Critics question whether biological function is sufficient to produce full propositional meaning, abstract thought, or logical obligation. A mechanism may have a selected function, but the statement that a conclusion ought to be accepted because it follows validly from premises appears stronger than the statement that a cognitive mechanism historically contributed to reproductive success.

Science Corrects the Limitations of Evolution

Paul Churchland has argued that Plantinga focuses too narrowly on our native cognitive equipment. Humans extend and correct their natural faculties through scientific institutions, symbolic systems, instruments, and communal investigation. On Churchland's view, Evolutionary Naturalism may draw its warrant from the collective operations of the scientific community even if it could find none in the unaided reasoning of a single human brain. We should therefore evaluate not only the individual mind but the broader truth-seeking practices that natural beings have developed.

This response explains how limited organisms may acquire knowledge far beyond the environments in which their ancestors evolved. Plantinga and Aaron Segal replied to Churchland directly, arguing that these institutional practices are themselves products and extensions of the very faculties whose reliability is in question, so that appealing to them does not escape the original difficulty.

The debate turns on this point. Scientific practices do not create rational standards from nothing. They presuppose that evidence should guide belief, that contradictions are defects, that repeated observations carry evidential weight, and that some methods are more truth-conducive than others.

The naturalist may be able to explain these standards. The argument from reason asks whether such an explanation can remain wholly descriptive without losing their normative authority.

Does Naturalism Defeat Itself?

The strongest version of the argument should not say:

Naturalism says the brain is physical. Therefore, no naturalist can reason.

That conclusion is much too quick.

A more careful argument proceeds conditionally:

1. Rational inference requires that the meaning and logical relationships of thoughts play a genuine role in the formation of belief.
2. Some forms of naturalism appear to explain belief formation entirely through nonrational physical causes.
3. If those physical causes leave no causal or explanatory role for meaning, truth, and logical implication, rational inference has not been adequately preserved.
4. Naturalism is itself accepted through rational inference.
5. Therefore, any form of naturalism that eliminates the efficacy or trustworthiness of rational inference undermines its own rational credentials.

This conclusion is more modest than declaring that every possible form of naturalism has been refuted.

There is a further reason the difficulty is hard to escape by argument alone. As Thomas Reid observed, reasoning cannot certify its own trustworthiness without circularity, for any such proof must already employ the faculty whose reliability is in question. This does not by itself favor theism, but it shows that confidence in reason functions as something closer to a starting point than a conclusion—and it presses the question of which worldview makes that starting point least surprising.

Naturalists have developed sophisticated theories of mental causation, emergent properties, functional organization, representation, and epistemic reliability. The philosophical discussion remains active because none of these questions has received a universally accepted answer. Mental causation itself remains a central and difficult subject within contemporary philosophy of mind.

Notably, the concern is not confined to religious thinkers. The atheist philosopher Thomas Nagel, in Mind and Cosmos (2012), argues that a reductive, materialist account of nature cannot adequately explain consciousness, cognition, or reason, and that our capacity to grasp objective truth sits uneasily within a purely Darwinian story. Nagel does not turn to theism; he calls instead for an expanded naturalism. But his discomfort illustrates that the problem the argument identifies is felt across worldviews, not manufactured by apologetics.

The argument therefore places an explanatory burden upon naturalism. It asks the naturalist to show how a reality that is not fundamentally mental, purposive, or norm-governed can produce beings whose thoughts possess meaning, whose inferences are governed by logical necessity, and whose minds can discover truths extending far beyond immediate reproductive needs.

Does Theism Explain Reason Better?

Christian theism begins from a profoundly different picture of reality.

The foundation of existence is not mindless matter but the eternal God. The universe proceeds from divine wisdom, and human beings are created in the image of God. The Gospel of John identifies Christ as the eternal Logos, the divine Word through whom all things were made (John 1:1–3). Reality is intelligible because it is the work of divine intelligence.

Within this framework, the correspondence between mind and world is not an inexplicable accident.

Human beings can discover order because both the human mind and the created order have their source in the same divine reason. Logical truth is not a temporary evolutionary convention, and our desire to know is not wholly detached from the nature of reality.

This does not mean that Christian theism promises infallible human reasoning. Scripture presents human beings as finite, morally fallen, vulnerable to self-deception, and dependent upon correction. The Christian account predicts both genuine cognitive ability and serious cognitive limitation.

Theism also faces philosophical questions. Believers must explain why a good God permits mistaken reasoning and how confidence in divinely created faculties avoids circularity. Appealing to God is not a substitute for examining evidence or acknowledging human bias.

Nevertheless, theism provides a metaphysical home for reason. Mind does not emerge as a surprising late arrival in a universe fundamentally alien to thought. Finite reason reflects, however imperfectly, the eternal wisdom from which creation receives its being.

This does not by itself prove Christianity. The argument from reason is best understood as part of a cumulative case. It asks which worldview makes the existence, authority, and trustworthiness of reason less surprising.

A Balanced Verdict

Can naturalism account for reason?

Naturalists have proposed substantial answers. Evolution can favor accurate perception. Physical and rational explanations may coexist. Cultural practices can correct innate biases. Naturalistic theories of representation and mental causation cannot simply be dismissed.

It would therefore be irresponsible to claim that evolution necessarily produces unreliable cognition or that no naturalist has any possible explanation for rational thought.

Yet the central difficulty remains.

A causal history explains how a belief came to exist. Rational justification concerns whether the belief should be accepted as true. An evolutionary function may explain why a cognitive mechanism persists. Logical validity concerns whether a conclusion follows necessarily from its premises. A neurological description may identify the brain processes involved in reasoning. It does not, by itself, explain why those processes possess meaning or why one inference is rationally superior to another.

Naturalism is not defeated merely because thought has physical causes. It encounters trouble when its account of those causes leaves no meaningful work for truth, evidence, and logical necessity to perform.

The argument from reason therefore does not rest upon mocking evolution or denying neuroscience. Its force lies in a quieter observation—the same one that unsettled Darwin: reason appears to reveal something about the kind of universe we inhabit.

If reality originates in reason, human rationality is not an accidental stranger in the cosmos. It is a finite participation in an order that was intelligible before we arrived.

Reflection

Christians should approach this argument with humility.

Our ability to reason is not evidence that we are immune to error. Intelligence can become an instrument of pride, and argument can be used to conceal truth as easily as to uncover it. The Christian confession is not that human beings reason perfectly, but that reason itself is a gift.

Christ, the eternal Logos, does not call us to abandon the mind. He calls us to love God with all of it.

Every valid inference, every honest correction, and every patient search for truth bears witness to a world that can be understood. We do not create truth by believing it. We receive it, pursue it, and submit ourselves to it.

The deepest purpose of reason is therefore not intellectual conquest. It is communion with the One through whom all things were made.

When reason is faithful to its calling, it does not terminate in human cleverness. It leads beyond itself—to wonder, gratitude, humility, and worship.

Sources:

• Anscombe, G. E. M. "A Reply to Mr. C. S. Lewis's Argument That 'Naturalism' Is Self-Refuting." In The Collected Philosophical Papers of G. E. M. Anscombe, vol. 2, Metaphysics and the Philosophy of Mind. University of Minnesota Press, 1981.

• Churchland, Paul M. "Is Evolutionary Naturalism Epistemologically Self-Defeating?" Philo 12, no. 2 (2009): 135–141.

• Darwin, Charles. Letter to William Graham, 3 July 1881. In The Life and Letters of Charles Darwin, edited by Francis Darwin, vol. 1. John Murray, 1887. (Also Darwin Correspondence Project, Letter no. 13230.)

• Dretske, Fred. Naturalizing the Mind. MIT Press, 1995.

• Fitelson, Branden, and Elliott Sober. "Plantinga's Probability Arguments Against Evolutionary Naturalism." Pacific Philosophical Quarterly 79, no. 2 (1998): 115–129.

• Lewis, C. S. Miracles: A Preliminary Study. Revised edition. Fontana/Collins, 1960. Especially chapter 3, "The Cardinal Difficulty of Naturalism."

• Millikan, Ruth Garrett. Language, Thought, and Other Biological Categories: New Foundations for Realism. MIT Press, 1984.

• Nagel, Thomas. Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False. Oxford University Press, 2012.

• Plantinga, Alvin. Warrant and Proper Function. Oxford University Press, 1993. Especially chapter 12.

• Plantinga, Alvin. Where the Conflict Really Lies: Science, Religion, and Naturalism. Oxford University Press, 2011. Especially chapter 10.

• Plantinga, Alvin, and Aaron Segal. "Response to Churchland." Philo 13, no. 2 (2010): 211–217.

• Reppert, Victor. C. S. Lewis's Dangerous Idea: In Defense of the Argument from Reason. InterVarsity Press, 2003.

• Reppert, Victor. "The Argument from Reason." In The Blackwell Companion to Natural Theology, edited by William Lane Craig and J. P. Moreland, 344–390. Wiley-Blackwell, 2009.

• Robb, David, and John Heil. "Mental Causation." The Stanford Encyclopedia of Philosophy.

• Schulte, Peter. "Teleological Theories of Mental Content." The Stanford Encyclopedia of Philosophy.

• Stoljar, Daniel. "Physicalism." The Stanford Encyclopedia of Philosophy.