For those who do not subscribe to a theistic worldview, we often explain our reasoning capabilities through an evolutionary process. A potential issue with this, known as the Evolutionary Argument Against Naturalism (EAAN), is that evolution has no reason to optimize for truth-seeking ability; it selects for survival and reproduction. Suppose there were certain truisms independent of the material world. Evolution has no inherent mechanism to develop beings capable of detecting them. This throws into question the validity of our reasoning capabilities. If our brains are merely survival machines, how can we trust them to know what is true?
For simplicity, let us first throw out the metaphysical contraband that is objective, Platonic truth. In other words, let us assume there is not some immaterial realm of perfect forms and concepts existing independently of the material world we interact with. From this standpoint, the problem becomes more manageable. Evolution clearly has a reason to create brains that are suited for modeling the environment around them. An organism that can accurately predict the trajectory of a predator, the location of a food source, or the social dynamics of its group will have a significant survival advantage.
These brains need not have the ability to grasp any abstract notion of “truth” to simply observe, model, and generate predictions about their environment. It certainly seems convenient, then, to trust our reasoning capabilities when they begin to generate shockingly accurate predictions about the world around us. The scientific method, arguably the most refined application of human reason, has allowed us to eradicate diseases, communicate instantaneously across the globe, and map the cosmos. Reason has also made a pretty good case against our other biological faculties. It is through careful reasoning and empirical testing that we have identified the myriad cognitive biases that cloud our perception and lead us to false conclusions. In this sense, reason is a self-correcting tool. It is the only faculty we possess that can critique itself, identify its own flaws, and build systems like formal logic and the scientific method to compensate for them. This pragmatic success is a powerful argument for the validity of our reason, at least as it applies to the physical world.
As a math lover, however, my earlier abandonment of objective truth was not without a hint of existential horror. On the one hand, there is the powerful intuition that mathematical and logical truths are discovered, not invented. Mathematical structure seems universal and necessary, independent of the contingent, biological minds that perceive it. On the other hand, there is the more scientific evolutionary explanation: that our capacity for logic and mathematics is a highly developed form of pattern recognition. The ability to abstract concepts of quantity, shape, and change from our environment was instrumentally useful for survival. Mathematics, in this view, is the powerful and internally consistent language we built upon these foundational, evolutionarily-honed abstractions. It feels objective because its axioms are rooted in the most basic, inescapable features of our physical reality, and its logical rules, once established, are unyielding. Its “truth” is a measure of its consistency and its descriptive power, not its connection to a transcendent realm.
This evolutionary account, however, invites a deeper challenge. It explains our intuitive grasp of axioms by grounding them in physical reality, but it seems to take for granted the validity of the deductive logic we use to build upon them. Why should we believe that evolution would equip us with a truth-preserving logical structure? The answer may be that the rules of inference themselves are an abstraction of the physical world’s fundamental consistency. This of course is new metaphysical baggage. But putting that aside, it would seem that an organism whose brain operated on a logic where contradictions were permissible or where cause and effect were muddled would fail to make reliable predictions. The principle of non-contradiction, for instance, is not just a formal rule but a reflection of a world where a thing cannot simultaneously be both food and poison, safe and dangerous. Therefore, our trust in deductive reasoning can also be seen as a product of evolution, a cognitive toolkit honed by the inescapable causal structure of the environment.
Having thrown out the metaphysical contraband of “truth,” we find ourselves with new metaphysical baggage: a fundamentally consistent physical reality. There really is no reason for the universe to be logically consistent. It could be the case that it is simply impossible for there to exist a physical reality where logical consistency does not exist. Whatever the case, we have arrived at an impasse where we do not have much choice but to trust the logical consistency of reality and our ability to grasp it.
In any case, there seems to be ample evidence for a fundamentally consistent physical reality as articulated by Eugene Wigner in his essay: The Unreasonable Effectiveness of Mathematics in the Natural Sciences. Wigner marveled at the fact that mathematical structures, often created by mathematicians for purely abstract or aesthetic reasons, later turn out to be the precise language needed to describe the fundamental laws of physics. That the universe is so orderly is nothing short of a miracle.