On Sawing off the Branch One is Sitting Upon*
By Melissa Cain Travis
Contemporary naturalists typically give “logic and reason” as the method by which they’ve arrived at their metaphysical conclusions. They consider themselves “freethinkers” who are intellectually unchained from what they regard as the irrational superstitions of religious belief. In their view, science is the ultimate arbiter of truth about the world, telling us (among other things) what does and does not exist. The irony is that naturalism effectively eliminates the possibility of genuine reason and free thought, thus destroying the epistemic foundation of the scientific enterprise. In Christian philosophy, this problem is highlighted by the so-called argument from reason (hereafter, AR).
Many who are at least somewhat familiar with the AR think of its winsome depiction in the third chapter of C.S. Lewis’s Miracles. Lewis explained that if “the whole interlocked system” of nature constituted all of reality (the worldview known as naturalism), then reasoning (as we commonly understand the term) would not exist. Thus, we could not achieve rational knowledge of anything, including whether naturalism itself is true. Rational knowledge, explains Lewis, requires what he called a “Ground and Consequent” relation between beliefs in a chain of reasoning. For instance, if we know that A = B and B = C, then by the transitive law of logic we conclude that A = C. We see that A must equal C because of the rules of correct reasoning. However, if a causally closed system comprised of the material brain and its chemical dynamics is the whole story of our mental activity, there can be so such thing as Ground and Consequent relations, only blind, material cause and effect. As Stewart Goetz has characterized Lewis’s assertion: “(1) If naturalism is true, then we do not reason. (2) We reason. (3) Naturalism is false.”[1] In essence, arguing for naturalism is a self-defeating exercise.
In contemporary philosophy, the AR has been understood, developed, and expanded in a variety of ways, notably by Alvin Plantinga (in his famous Evolutionary Argument Against Naturalism) and Victor Reppert, whose excellent book, C.S. Lewis’s Dangerous Idea, discusses the various interpretations of the AR and develops his preferred version. However, there is a rich intellectual history that includes some of the key ideas behind the argument; the AR by no means began with Lewis. In fact, it would be fair to say that the necessity of immaterial elements (of one sort or another) in the account of human reasoning is one of the Great Ideas of Western thought, beginning with the ancient pagans and then gradually blossoming during the Christian era. For example, we see bits and pieces of this very long conversation in Plato, St. Augustine, Descartes, Locke, Reid, Kant, and Aruthur James Balfour, whose Theism and Humanism made Lewis’s top ten list of most influential books.
It is fascinating to note that at least two renowned scientists of Lewis’s day were among those who saw significant problems with a materialist account of human rationality. J.B.S. Haldane (1892–1964), an atheist mathematician and biologist, said, “If materialism is true, it seems to me we cannot know that it is true. If my opinions are the result of the chemical processes going on in my brain, they are determined by chemistry, not the laws of logic.”[2] In other words, blind chemical processes cannot take principles of good reasoning into account and therefore do not constitute genuine rationality (even though such processes could accidentally produce a result that conforms to the laws of logic). In his essay, “Possible Worlds,” Haldane writes:
It seems to me immensely unlikely that mind is a mere by-product of matter. For 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. They may be sound chemically, but that does not make them sound logically. . . In order to escape from this necessity of sawing away the branch on which I am sitting, so to speak, I am compelled to believe that mind is not wholly conditioned by matter.[3]
A key thing to notice about this passage is the statement about the chemical activity of the brain not making mental content compatible with the external, immaterial laws of logic. Haldane goes on to say that when he engages in logical, scientific, and moral thinking, “I am already identifying my mind with an absolute or unconditioned mind.”[4] He seems to mean that objective standards, such as those required for correct mental deliberation and morality, directly imply a transcendent rational source. Haldane’s tree branch analogy indicates that he saw the materialist account of mind as self-defeating; if the mind is only matter in motion, we do not actually reason, and therefore we cannot rationally conclude that the materialist position is correct.
Hermann Weyl (1885–1955), a German theoretical physicist and mathematician who contributed to cosmology and quantum mechanics, was not a religious man in any traditional sense. His concept of the divine bore resemblance to Einstein’s somewhat Spinozan view; he defined God as “the completed infinite,” as mathematics itself.[5] Weyl perceived the problem materialism posed for human rationality. In his book Mind and Nature he writes, “When I reason that 2 + 2 = 4, this actual judgment is not forced upon me through blind natural causality (a view which would eliminate thinking as an act for which one can be held answerable) but something purely spiritual enters in: the circumstance that 2 + 2 really equals 4, exercises a determining power over my judgment.”[6] Weyl seems to mean that when we reason, we are able to take mathematical rules into account and freely direct our mental processes towards truth. If the mind is wholly the result of inevitable physical processes, however, it simply turns input into output by way of neurochemical reactions that can have no concern for truth. As Lewis pointed out, our thoughts have about-ness, whereas mere matter does not.
Thus, both Haldane[7] and Weyl realized that human reason requires having Ground and Consequent relations, the ability to exercise free judgment in a truth-aimed way, and the ability to see that a thought process aligns with the immaterial laws of logic and mathematics. It should be noted that later in his career, as a result of the development of early computers—machines that could be programmed to function according to the rules mathematics—Haldane became more open to the possibility of a materialist account of the rational mind. Some contemporary artificial intelligence theorists hold that machines will one day achieve reasoning on par with—or far exceeding—human capacities. However, one may respond by pointing out that blind computation falls far short of providing a comprehensive account of genuine rationality, for reasons that include those articulate by the aforementioned thinkers. As they—and subsequent philosophers of mind—have argued, we have very good reasons to believe that there is much more to the story than the “whole interlocked system” of matter and energy behaving according to the laws of nature.
—Melissa Cain Travis holds a PhD in Humanities (Philosophy) from Faulkner University's Great Books program and an MA in Science and Religion from Biola University. She is a Fellow at Discovery Institute’s Center for Science and Culture, where she teaches adult education courses related to the intersection of science, faith, and philosophy. To learn more about her publications and academic interests, visit melissacaintravis.com.
*This piece was originally published in The Worldview Bulletin Newsletter.
[1] Stewart Goetz, “The Argument from Reason,” Philosophia Christi Vol. 15, No. 1 (2013), 51.
[2] J.B.S. Haldane, The Inequality of Man (London: Chatto & Windus, 1932), 162.
[3] J.B.S. Haldane, “Possible Worlds” in Possible Worlds (New York: Routledge, 2017), 209.
[4] Haldane, “Possible Worlds”, 210.
[5] Peter Pesic, Mind and Nature: Selected Writings on Philosophy, Mathematics, and Physics (Princeton: Princeton University Press, 2009), 12.
[6] Hermann Weyl, Mind and Nature (Princeton: Princeton University Press, 2009), 52.
[7] We know that Lewis was at least somewhat familiar with Haldane’s view, as he very briefly mentions it in Miracles.