Reppert’s _C. S. Lewis’s Dangerous Idea_: A Review

C.S. Lewis’s Dangerous Idea: In Defense of the Argument from Reason.
By Victor Reppert. InterVarsity Press, 2003; 132 pages.

Like many of us, Victor Reppert, Professor of Philosophy at Glendale Community College in Arizona, has long been intrigued by the thought of C. S. Lewis, especially his so-called argument from reason (most fully developed by Lewis in chapter three of his book Miracles: A Preliminary Study). The author of numerous articles on Lewis’s arguments, Reppert provides his readers a fresh, clear, and able exposition and defense of what he calls C. S. Lewis’s dangerous idea: that a purely naturalistic account of the world cannot explain the reality of human rationality.

In the first of six chapters, Reppert tackles the unfortunate and misguided tendency of many to dismiss Lewis’s arguments as less than serious. This, he observes, is often a result of “the personal heresy,” that is, “focusing on Lewis himself rather than what he had to say” (p. 28). For example, given his preoccupation with other matters, Lewis did not offer detailed responses to many of the major philosophical problems of his day, thus costing himself—in the eyes of many, at least—the status of “real philosopher” (p. 20), never mind the success of his arguments. This sentiment is shortsighted indeed; Lewis’s thought, Reppert argues, deserves fair and honest consideration.

Before approaching Lewis’s argument from reason (AFR), Reppert spends chapter two discussing how we are to go about assessing apologetic arguments. Reppert frames his discussion in terms of three views on the relationship between faith and reason: fideism, strong rationalism, and critical rationalism. He concludes that a critical rationalist approach, that is, one that claims “religious belief systems can and must be rationally criticized and evaluated,” is most appropriate for studying Lewis’s arguments (p. 36-37).

Chapter three, the longest of the book, introduces the argument itself. The crux of the argument is whether a naturalistic worldview possesses the resources to explain humans’ ability to draw rational inferences, that is, to reason. At base, naturalistic explanations must appeal to the blind, mechanistic operations of nature; naturalists have no recourse to purposive explanations for rationality. The alternative, of course, is that we’re created in the imago dei, which Christians have long understood to include rational intellect (e.g., Thomas Aquinas, Summa Theologica Ia q. 93 a. 4 or The Westminster Confession, chapter 4). Lewis and Reppert, of course, affirm the theistic account.

After carefully explaining the naturalists’ account, Reppert moves to present the original version of Lewis’s AFR: simply put, that materialism (a popular version of naturalism) requires all beliefs to be based on irrational causes and that beliefs based on irrational causes should be rejected, thus materialism should be rejected. And here is where Reppert shines as both philosopher and biographer: On 2 February 1948, philosopher Elizabeth Anscombe and Lewis had a now famous exchange on the latter’s AFR—an exchange which has, unfortunately, been greatly misunderstood. Reppert clearly articulates the details of Anscombe’s criticisms, then presents the revised version of Lewis’s AFR.

The AFR, like many other arguments, is actually a family of arguments—a fact not lost on Reppert. He spends chapter four examining seven formulations of the AFR, each appealing to different features of reality to debunk naturalistic worldviews. Interestingly, these features of reality (e.g., truth and consciousness) are necessary to both naturalists and theists alike (on pain of irrationality), but as Reppert shows, they cannot be explained naturalistically. This implies the necessity of “explanatory dualism,” which is simply the affirmation that “while some events in nature can be explained [by] purely mechanistic causes, the elements of rational inference…cannot” (p. 87).

Developing the concept of explanatory dualism, Reppert spends the fifth chapter fielding popular objections to the AFR. Of particular interest are his discussions of intentionality or “aboutness,” in which he (in good Lewisian form) argues that one’s mental states are causally effective in the physical world (one decides to do things); “human beings possess rational powers that are impossible for beings whose actions are governed entirely by the laws of physics” (p. 87). He concludes that a theistic worldview can account for such significant realities, while a naturalistic worldview cannot.

The sixth and final chapter addresses the so-called “inadequacy objection,” that is, the “prevailing conviction that when the best naturalistic resources available are employed to produce an understanding of the world and mysteries [e.g., minds] are left over, we do little or nothing to explain those mysteries by invoking ‘souls’ or by explaining them in terms of God” (p. 106), particularly as set-forth by outspoken atheist Keith Parsons.

C. S. Lewis’s Dangerous Idea is a fine work. Well-written, it glows with Reppert’s engaging style and ability as an incisive thinker. At times demanding but not impossibly so, Reppert’s exposition and defense of Lewis’s argument from reason are of tremendous apologetic value.

Reviewed by R. Keith Loftin
Apologetics Resource Center

7 Responses to Reppert’s _C. S. Lewis’s Dangerous Idea_: A Review

  1. Thanks for this review. Readers might be interested in this response to some criticisms of my book, by Darek Barefoot.

  2. Keith says:

    Dr. Reppert, thank you for stopping by. I enjoyed your book immensely and have recommended it to many of my friends and colleagues.

    Thanks also for providing the linked information.

  3. glach says:


    Just to let you know, Johnny-Dee and myself (over at Fides Quaerens Intellectum) have a double book review of Menuge’s Agents Under Fire and Reppert’s Lewis book forthcoming in Faith and Philosophy. Thanks.

  4. Civis says:

    I decided to read HOW SHOULD WE THEN LIVE? earlier this week. In the first chapter, Schaffer said that people’s lives are driven by their world view and their preconceptions about the world to an extent even they do not realize.

    If this is true, why is it that people’s actions so often do not match their words? But why is there such a disconnect between words and actions if this is true? Are the things we say just a bunch of empty platitudes that we don’t really mean? It seems we say things, and we mean them, but then we often do not act accordingly. To quote a different scripture that might appear to contradict the proverb, Paul talked about the war within his flesh etc. and said “what I want to do I do not do, and what I do not want to do I do.”

  5. Keith says:


    Please forgive my delayed response. Thank you for the heads-up. I receive F&P, so I’ll be eagerly awaiting your review.


    It’s great that you read _How Should We Then Live_, but I’m curious about why you saw fit to inform us of that here.

  6. Civis says:

    Because I found this blog by googling worldview and Schaffer, and a friend who got me to read this book said you guys knew about this stuff. Sorry if I threw you off. I guess I should have introduced my question better.

  7. […] Reppert, author of C. S. Lewis’s Dangerous Idea (which I recently reviewed here), has some things to say about “Dawkins on C. S. Lewis and the trilemma” on his blog […]

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