C.S. Lewis and the argument from reason

by Jay W. Richards

To see Lewis’s genius, I’d like to focus on one of his best-known arguments — often called the “argument from reason.” The purpose of the argument is to show that naturalism and reason are incompatible, that believing in naturalism is self-defeating. That is, if naturalism is true, then we ought not to trust our capacity for reason, and so, ought not to trust arguments in favor of naturalism.

Philosopher Victor Reppert describes the argument (and several versions he develops from Lewis’s original) as “beginning with the insistence that certain things must be true of us as human beings in order to ensure the soundness of the kinds of claims we make on behalf of our reasoning.”1 This argument gained attention when Lewis proposed it in the first edition of Miracles. Philosopher Elizabeth Anscombe critiqued the original formulation of the argument, so Lewis corrected it in a subsequent edition of Miracles.2 It is this revised version of his argument that millions of readers have encountered. (He also discusses the argument in some lesser-known articles published in Christian Reflections and God in the Dock.)

Lewis taught philosophy in his first year as a lecturer at Oxford, but he wasn’t a professional philosopher. Moreover, he made the argument from reason in a small book written for public consumption. And yet it has been remarkably resilient and fruitful. Its philosophical offspring still play a role in contemporary philosophy. The most rigorous form of the argument is the “Evolutionary Argument Against Naturalism” developed and refined by philosopher Alvin Plantinga.

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The Basic Argument

Miracles is not a historical defense that miracles have actually occurred. It is a preliminary defense of their possibility and propriety. One of its central arguments is that we cannot determine the antecedent probability of a miracle without first deciding what reality is like. If you think that a transcendent exists, for instance, you will assess the evidence for a miracle differently than if you are a naturalist who believes that the closed, interlocking system of nature is all that exists. As a result, Lewis spends a good deal of time in Miracles evaluating the competing claims of what he calls supernaturalism and naturalism.

It is in this context that Lewis takes up the so-called “cardinal difficulty of naturalism.” Naturalists in Lewis’s day were very much like naturalists in our day. They normally imagine that their philosophy is the result of sound reasoning and solid evidence, and assume non-naturalists are ignorant and irrational. Lewis argues quite the opposite: naturalism is not compatible with knowledge and the reliability of reason.

Naturalists, like everyone else, generally trust their reason to lead them to truth. We all take it for granted that we can learn about the world around us through our senses. We experience heat and sound and color and other people. We somehow synthesize and take account of these things with our mind. From these experiences we make inferences about the world…


C.S. Lewis and the argument from reason | Logical Faith