The Cardinal Difficulty of Naturalism

Big idea

Summary

Lewis presents what he calls the cardinal, or central, difficulty facing Naturalism: it cannot, without contradicting itself, account for human reasoning. If Naturalism is true, every event, including every thought that occurs in a human brain, is fully explained as the product of a long chain of non-rational physical and chemical causes. But reasoning claims something more than simply being caused: when we say 'B follows logically from A,' we are claiming a relation of ground and consequent, not merely of cause and effect — we are claiming that we see B to be true because A is true, not merely that some prior brain event happened to produce the thought B.

If our beliefs are, at bottom, only the last links in an unbroken chain of non-rational causes stretching back through chemistry and physics, Lewis argues, we have no standing ground from which to say any of them are true rather than merely caused. This applies with full force to the belief in Naturalism itself: if Naturalism is correct, the belief that Naturalism is correct is itself just one more non-rationally caused event, and there is no reason to suppose non-rational causes reliably produce true beliefs about the ultimate nature of reality. The Naturalist's own position, pushed far enough, undermines the very reasoning by which it was reached.

Lewis takes care — famously revising this chapter for the 1960 edition after the philosopher Elizabeth Anscombe pressed him on the point in a 1948 debate at Oxford's Socratic Club — to distinguish 'non-rational' causes from merely 'irrational' ones. His claim is not that a causally produced belief must be false, but that being merely caused cannot, by itself, be a reason for believing it true; a cause explains why a thought occurred, but only a valid inference can explain why it ought to be believed. Naturalism, taken all the way down, treats every act of reasoning as pure occurrence and none as genuine insight, which leaves it unable to explain how anyone, including the Naturalist, could ever know anything — including Naturalism — to be true.

The chapter's constructive move is therefore this: because we do trust at least some of our reasoning (we have to, even to mount an argument against trusting it), there must be something about valid reasoning that is not merely one more link in Nature's non-rational causal chain. Human reason, Lewis concludes, has to be in some sense derived from a supra-rational source rather than being wholly a product of Nature acting on itself — which is already a small but real breach in a strictly Naturalist account of reality, prior to any discussion of miracles proper.

Key points

• Reasoning claims a relation of 'ground and consequent' (this is true because that is true), which is a different kind of connection than mere cause-and-effect.
• If Naturalism is true, every thought — including the thought that Naturalism is true — is simply the last link in a chain of non-rational causes, giving us no standing ground to call any belief true rather than merely caused.
• This isn't a claim that caused beliefs are automatically false, only that being caused, by itself, cannot make a belief rational or trustworthy.
• Lewis revised this chapter for the 1960 edition to sharpen the distinction between a 'non-rational' cause and an 'irrational' one, after philosopher Elizabeth Anscombe's 1948 critique at the Socratic Club.
• Because we do trust at least some of our own reasoning (we must, even to argue against it), reason cannot be wholly a product of non-rational Nature acting on itself alone.

Illustrations & analogies

• Lewis pictures the naturalist's own act of arguing for Naturalism as a man trying to saw off the branch he is sitting on: the very reasoning used to prove that all reasoning is merely caused would, if true, undercut the reliability of that proof as well.
• The contrast between 'because' as used for a cause ('the branch snapped because of the wind') and 'because' as used for a reason ('I believe it will rain because the sky is dark') is used to show two fundamentally different kinds of connection that Naturalism tries to collapse into one.

For reflection and discussion

1. Lewis argues that trusting our own reasoning already commits us to something beyond a purely Naturalist account of the mind. Does this argument feel persuasive to you, or does it feel like a philosopher's trick?
2. Can you think of a case where you accepted a conclusion mainly because of how it was caused (upbringing, mood, self-interest) rather than because of the reasons actually given for it?