The title of Dr. Reppert's "C.S. Lewis' Dangerous Idea" was inspired by Daniel Dennett's "Darwin's Dangerous Idea."
Darwin's dangerous idea, according to Dennett (a philosopher of the materialist school) is that all things, in the final analysis, can be explained not by teleological principles of meaning and intelligence, but by mechanistic processes. Also, materialists hold that the physical world (which comprises all things) is causally closed. The existence of everything thing and the occurrence of every event is due to a prior physical cause. Mental states (which extreme materialists deny exist at all) are considered to be determined by the physical processes of the brain. Thus, materialism holds that we acquire knowledge of the world and of ourselves through science (all things in existence being governed by the laws of physics).
C. S. Lewis' "dangerous idea" is that scientists draw their conclusions from evidence through rational inference. But can materialism account for human reason itself? Lewis and Reppert argue convincingly that it cannot.
In the first two chapters, Reppert refutes what he calls the "Anscombe Legend." This refers to a public exchange at Oxford that Lewis had with Catholic philosopher Elizabeth Anscombe. Many of Lewis' critics such as A. N. Wilson, Humphrey Carpenter, and John Beversluis have written that Anscombe so devastatingly refuted Lewis' argument from reason published in his "Miracles" that he abandoned Christian apologetics for good and was reduced to writing children's stories.
Reppert argues that even if this were true (which it isn't) it would tell us nothing about the value of either of their theories. It certainly would not confirm that the arguement from reason is wrong, but this is precisely what his critics claim it does. As Reppert shows, the encounter itself has been hugely overblown. Lewis taught philosophy at Oxford and was quite familiar with professional philosophers. Others who attended the debate did not believe it was terribly dramatic. Anscombe herself provides a moderate account of its importance in her memoirs. Lewis himself revised his argument in the next edition of "Miracles." He did not abandon his position and this is evident in the subsequent articles and books he wrote.
One of Anscombe's criticism's was that Lewis was wrong to say that "If materialism is true it can be fully explained as the result of irrational causes." Lewis simply corrected the problem by substituting "nonrational" for "irrational". This doesn't seem like a big deal. More importantly, Anscombe argues that "reasons-explanations are not causal explanations and therefore cannot compete with causal explanations" .
Lewis' revised argument was [57-8]:
(1) No belief is rationally inferred if it can be fully explained in terms of nonrational causes.
(2) If materialism is true, then all beliefs can be fully explained in terms of nonrational causes.
(3) Therefore, if materialism is true, then no belief is rationally inferred.
(4) If any thesis entails the conclusion that no belief is rationally inferred, then it should be rejected and its denial accepted.
(5) Therefore materialism should be rejected and its denial accepted.
Anscombe (following Wittgenstein) argues that the claim that naturalistic causes exist for every event does not, as Lewis argues, mean that no belief can be rationally inferred. A person may still be rational and sincerely believe that X entails Y, regardless of causation. But the subject is rational inference. Through it, what we come to know is logical connection and a logical connection is not any particular spatio-temporal location . Anscombe cannot severe reasons and causes in this way. The criticism is that materialism cannot provide an account of the role that convincing plays in cognition. If reasons cannot be a cause of our beliefs than we do not possess reason in any meaningful sense. But we do possess meaningful rational ability. Otherwise we could not be convinced, or fail to be convinced, on the persuasiveness or lacktherof of Anscombe's argument, that we do not possess it. This is the central problem for the materialist. Science depends on rational inference. Materialism is firmly committed to scientific explanation. But materialism denies rational inference.
In Chapter Four, Reppert offers several different formulations of the argument from reason:
(1) The Argument from Intentionality:
Thoughts are "about" things. But it makes no sense to say that one physical state is about another physical state. Rational inference implies the existence of "aboutness." Thus, materialism is false.
(2) The Argument from Truth:
We have the ability to discriminate between truth and falsity. But to talk about one physical state being true of another physical state makes no sense. Rational inference implies that states of a person can be true or false. Thus, materialism is false.
(3) The Argument from Mental Causation:
We rationally infer by way of mental causation. One mental state can cause another mental state in virtue of its propositional content. If, as materialists hold, mental causation does not exist, one could not, for instance, come to believe in Darwinism based on the persuasiveness of its premises. Rational inference implies that mental causation is real. Thus, materialism is false.
(4) The Argument from the Psychological Relevance of Logical Laws:
Rational inference involves the laws of logic. Unlike physical laws, these tell us what must be true not only in this physical universe, but any possible universe we can imagine, including one in which the laws of physics do not hold. But a materialist account of knowledge must hold that knowledge is gained through a causal interaction between the brain and the object of knowledge. But if we know or have insight into the laws of logic we must be in a physical relationship with the laws of logic. This makes no sense. Thus, materialism is false.
(5) The Argument from the Unity of Consciousness in Rational Inference:
If one infers P from Q, this means that one has a complex awarness of P, and of Q, and the logical connection between them, and thus concludes that since Q, then P. If materialism is true then each of these moments of awareness is a different brain process. But there must be a metaphysical unit that allows the simlutaneous awareness of all these moments. Our first-person experience of rational inference tells us this is so. Thus, materialism is false.
(6) The Argument from the Reliability of Our Rational Faculties:
Materialism holds that our faculties are the result of naturalistic evolution. Natural selection favors the development of reliable cognitive and rational abilities on to the extent that they help us cope with our environment. But there is no reason to believe that our advanced rational capacity is a reliable guide to the external world if materialism is true. Logical laws are knowledge we have nonempirically. But such knowledge does not help us find food, build shelters, or even produce a viable society. Survival requires effective response to the environment, not accurate knowledge of that environment. Evolution could select for something inaccurate in depicting the environment but efficient at producing the biologically correct response to the environment. Rational inference implies that logical laws do exist and have causal ability. Thus, materialism is false.
In Chapter Five, Reppert explains his theory of "Explanatory Dualism" by which he means that whlie some events can be explained in purely mechanistic terms, the elements of rational inference cannot. Human beings possess rational powers that are impossible for beings whose actions are governed only by physical laws .
In response to those that raise the issue of Cartesian mind-body dualism (which he quotes William Hasker as saying "may well hold the all-time record for overrated objections to philosophical positions")points out that Hume showed that we really don't know of any necessary connection in the causal relationships between physical objects. He argues that the soul may or may not have a spatial location (and thus may be a peculiar form of matter than exists outside of the normal causal chain. He also argues that dualism does not and should not require that the mind exist in radical independence from the physical brain. Thus, Charles Taliaferro writes about "integrative dualism", according to which a person is not identical to their body but the life of the mind is nonethless heavily dependent on the brain. But it is not determined by, or synomomous with, the brain.
All in all, this is a concise and effective argument against materialism and a defense of theism and rationality properly understood.