Reppert argues that the existence of human reason gives us good reason to suppose that God exists. If the world were as the materialist supposes, then we would be unable to reason to this conclusion. This contention is often challenged by the claim that mental and physical explanations can be given for the same event. But a close examination of the question of explanatory compatibility reveals that the sort of explanation that would have to be given for the events of inferring that atheism is true, for example, is incompatible with the event being explicable as a purely physical product of a physical universe.
"In C. S. Lewis's Dangerous Idea: In Defense of the Argument from Reason (InterVarsity: 2003), Victor Reppert has contributed what is surely the most extensive defense of the so-called 'Argument from Reason' yet to appear in print. In this critique, I will point out what I believe are the most important conceptual flaws in his arguments, and explain in detail how his arguments are ineffective against my own personal worldview."
C. S. Lewis's argument from reason (AfR) claims that the process of inference by which consideration of premises causes us to adopt a conclusion cannot be coherently conceived of in terms of physical cause-and-effect alone. In C. S. Lewis's Dangerous Idea, Victor Reppert maintains that the argument still poses a strong challenge to naturalism. However, Richard Carrier has attempted to refute Reppert's version of the AfR by invoking developments in cognitive science and computational theory. In this essay Darek Barefoot argues that advances in cognitive science do not affect the AfR since there is an absolute conceptual divide between rational mental causes and physical computational ones. Furthermore, if the AfR is successful, it reveals that rationality is fundamental to the universe, not simply a by-product of physical cause-and-effect; and this, in turn, is readily explicable on theism, but problematic for naturalism.