reasonable ground. Knowledge, however, is apprehended by reasoning from ground to consequent. Therefore, if naturalism were true, there would be no way of knowing it, or anything else not the direct result of a physical cause. Lewis asserts that by this logic, the statement "I have reason to believe naturalism is valid" is self-referentially incoherent in the same manner as the sentence "One of the words of this sentence does not have the meaning that it appears to have", or the statement "I never tell the truth". In each case, to assume the veracity of the conclusion would eliminate the possibility of valid grounds from which to reach it. To summarize the argument in the book, Lewis quotes J. B. S. Haldane who appeals to a similar line of reasoning. Haldane states "If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true ... and hence I have no reason for supposing my brain to be composed of atoms." Revisions The original version of Miracles contained a different version of chapter 3 entitled "The Self-Contradiction of the Naturalist". In it, Lewis made the same argument but referred to atomic motions in the brain as "irrational". In a Socratic Club debate, Catholic analytical Thomist G. E. M. Anscombe criticized this, prompting Lewis to revise the chapter. The revised chapter presents a more detailed elucidation of the argument and distinguishes between "non-rational" and "irrational" processes. Anscombe commented on the process after Lewis's death that the rewrite showed "honesty and seriousness" on the part of Lewis. See also Evolutionary argument against naturalism Argument from reason Socratic Club The Anscombe Myth References Footnotes Sources John Beversluis C.S. Lewis and the Search for Rational Religion. Grand Rapids, Michigan: William B. erdmans, 1985. C.S. Lewis Miracles. London & Glasgow: Collins/Fontana, 1947. Revised 1960. (Current edition: Fount, 2002. ) Victor Reppert C.S. Lewis's Dangerous Idea. Downers Grove, Illinois: InterVarsity Press, 2003. G.K. Chesterton Orthodoxy. New York, New York: Barnes and Noble, Inc., 2007; originally published in 1908. Quotations and Allusions in Miracles at Lewisiana.nl External links Books by C. S. Lewis Miracles 1947 non-fiction books 1960 non-fiction books Geoffrey Bles books