Faith & Science Icon Faith & Science

Descartes’s Blunder

Michael Egnor

René Descartes

What is it that we are most sure of? It’s a fundamental question, the object of philosophical analysis for millennia. Our modern answer to this question was provided by René Descartes in the 17th century. Descartes’s answer is the answer most modern men would give. But Descartes got it wrong.

Descartes set out to rethink metaphysics from the ground up. In Meditations on First Philosophy, he asked this question: How do I know what is real? Of what can I be certain? He suggested this scenario: Imagine that his mind is controlled by an evil demon. The demon is of “upmost power and cunning [and] has employed all his energies in order to deceive me.” How, he asked, could he know whether or not this were the case? Descartes doubted the reliability of his senses: they can deceive, he believed. Of what can he really be certain?

He concludes, famously, that he can be certain only of this: that he exists. Cogito ergo sum. Because even to doubt his own existence presupposes his existence.

This metaphysic of radical skepticism forms the basis for much of Descartes’s metaphysics, which we moderns have (largely unconsciously) inherited.

But Descartes is misguided (and not by a demon). Most fundamentally, he is wrong about the thing that we are most sure of.

The foundation of epistemology is not self-awareness. This can be understood by considering Descartes’s maxim, “Cogito ergo sum.” Notice that we cannot conclude that we exist unless we can conclude. That is, we must first know the principle of non-contradiction — that being is not non-being — before we can conclude that “I think therefore I am.”

“Therefore,” not “I think” nor “I am,” is the crux of the most important thing we know. The principle of non-contradiction is prior to self-awareness.

This is a foundation of Thomistic philosophy. St. Thomas notes:

By nature our intellect knows being and the immediate characteristic of being as being, out of which knowledge arises the understanding of first principles, of the principle, say, that affirmation and denial cannot coexist (opposition between being and non-being) …

(Summa Contra Gentiles: II, 83. Cf Ia IIae, q. 94, a.2.)

Aquinas derives his principle from Aristotle’s principle of non-contradiction: a thing cannot be and not be at the same time. It is the most fundamental thing we know, because if we do not know it, even Descartes’s first principle — cogito ergo sum — is not true. If being and not being could coexist, if contradiction were metaphysically possible, then it would be possible for me to think and at the same time not to exist.

The law of non-contradiction, not cogito ergo sum, is the foundation of knowledge.

It’s worth noting that modern atheists and materialists have a particular problem with non-contradiction. Consider a number of atheist and materialist claims in this light.

Materialists and atheists claim that ID is scientifically wrong, and claim that ID is not scientifically testable. But of course, in order to be scientifically wrong, ID must be scientifically testable.

Materialists and atheists believe that our minds evolved by natural selection. But if we evolved wholly by natural selection, we evolved to maximize reproductive success, not to discern truth, and thus we could not trust our belief that we evolved by natural selection.

Materialists and atheists believe that determinism is true and that free will is not real. But if determinism is true and we lack free will, then our opinions are determined by physical processes, which are not propositions and which lack truth value. Chemical reactions are neither true nor false, so a materialist’s opinion that determinism is true and free will is not real has no truth value.

Materialists and atheists believe that the universe spontaneously came from nothing, and they define nothing as the laws of quantum mechanics.

Materialists and atheists believe that the existence of evil disproves the existence of God, yet if there is no ultimate Source of right and wrong, there is no evil and no good; there are merely circumstances we like or dislike. Nietzsche, unlike the New Atheists, understood this.

Again and again, materialists and atheists hold opinions that violate the law of non-contradiction. In this sense, atheism and materialism aren’t even really metaphysical theories. They’re just self-refuting nonsense.

Image: Portrait of René Descartes, by Frans Hals, via Wikimedia Commons.