C. S. Lewis is kinda wrong

This version of the argument from reason isn't convincing. There are better ones.

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Years ago, I encountered C. S. Lewis in the form of his book Mere Christianity—an excellent read that I highly recommend, whatever one’s religious or philosophical beliefs. In any case, I recently came across his version—or one such version, anyway—from the argument from reason to the existence of God. The quote from The Case for Christianity is popular. Here it is:

Supposing there was no intelligence behind the universe, no creative mind. In that case, nobody designed my brain for the purpose of thinking. It is merely that when the atoms inside my skull happen, for physical or chemical reasons, to arrange themselves in a certain way, this gives me, as a by-product, the sensation I call thought. But, if so, how can I trust my own thinking to be true? It's like upsetting a milk jug and hoping that the way it splashes itself will give you a map of London. But if I can't trust my own thinking, of course I can't trust the arguments leading to Atheism, and therefore have no reason to be an Atheist, or anything else. Unless I believe in God, I cannot believe in thought: so I can never use thought to disbelieve in God.

The idea here, in a nutshell, is that we shouldn’t trust our reasoning if it were not designed for reliability. If our thoughts do not track reality—in other words, if what we think is real isn’t, or vice versa—then we have reason to distrust even the thought that our thinking wasn’t designed. This is because even the thought my thinking wasn’t designed to be reliable or track the truth would be suspect—after all, it came from a mind that wasn't designed to uncover truth!

So far, so good—we cannot trust the veracity of our thoughts unless we have reason to think they are reliable, or at least we lack reason to think them unreliable. From there, Lewis concludes that there must be God—a powerful and loving agent who ensures that our cognition is reliable enough to be trusted.

The problem, though, is that an atheist has a good reply here: there are good reasons to expect that evolution would ensure our thinking and cognition are sufficiently reliable for no other reason than it would better enable us to survive and thrive. As philosophers Boudry and Vlerick argue:

True beliefs are better guides to the world than false ones. This is the common-sense assumption that undergirds theorizing in evolutionary epistemology. An early hominid who believes that tigers are dangerous predators, and acts upon that belief, will fare better (in terms of survival and reproduction) than one who believes that they are docile pets. Given that our brain has evolved to aid our survival and reproduction (as any biological organ), we can expect it to be geared towards churning out true beliefs. False beliefs, or cognitive mechanisms that tend to produce such beliefs, are mostly harmful and will be weeded out by natural selection.

So to return to the analogy Lewis gave: ‘But, if so, how can I trust my own thinking to be true? It's like upsetting a milk jug and hoping that the way it splashes itself will give you a map of London.’ Bad analogy. A better analogy would be this: of course I can trust my own reasoning because I am descended from ancestors whose cognition and thinking was honed for reliability due to natural and sexual selection pressures. People whose cognition and thinking were not sufficiently reliable would be more likely to be killed and thus fail to pass along the genes for their poor cognition to others. So, a better analogy: it would be like trusting an upset milk jug to reveal the location of London except that, for whatever reason, inaccurate milk jugs would have (likely) been eliminated.

Does this mean that this argument from reason is a failure? Perhaps, but there are others that may do better. However, that is another post for another time.