Plantinga’s evolutionary argument against naturalism

Alvin Plantinga’s evolutionary argument against naturalism (EAAN) focuses on beliefs and the cognitive faculties that produce them.

The key to understanding the EAAN is to follow Plantinga as he makes a careful distinction between two aspects of beliefs. The first aspect is the neurophysiological (NP)–the arrangements of neurons, electro-chemical impulses, pathways, and other structures and events that comprise the physiological manifestation of the belief. The second is the propositional content of the belief (all bachelors are unmarried; for all right triangles, the sum of the square of the two short sides equals the square of the hypotenuse, etc.).

Only the latter can be said to be true or false. But only the former can be affected by evolutionary dynamics as described in the naturalist account (i.e., no God, no design, only random mutation plus culling through natural selection).

Organisms that have fitness-enhancing NP structures will tend to survive and have offspring, while those that don’t won’t. Some of these NP structures may grow in complexity across generations to the point where belief formation happens, but again, the process that drives and shapes this growth can only ever affect the “NP side” of the belief. The “content side” is not affected whatsoever by this process, simply because the process is mindless and there is nothing there “behind the scenes” to endow organisms with the capacity to evaluate the truth or falsity of the propositional content of a belief, or even to be aware that such things as organisms or beliefs exist at all. Evolution selects for fitness, not for truth.

So on the naturalist account, only the NP properties of a belief can be subject to the dynamics and pressures of evolution, and those dynamics and pressures select for adaptive behavior/fitness only, full stop. According to the theory, there can be nothing else whatsoever going on. The propositional content side is simply not in play. Thus there is no reason to believe on naturalism + evolution that your belief-producing faculties can reliably generate true beliefs.

What all of this entails is that the person who believes that his belief-producing cognitive faculties are strictly a product of naturalism + evolution believes something that, according the belief itself, is produced by unreliable cognitive faculties. A person who understands this cannot sensibly believe both that his belief-producing faculties are reliable and that his belief-producing faculties are strictly the product of naturalism + evolution. The theory undercuts itself and should be abandoned.

The EAAN is not merely a very interesting and effective argument against naturalism. It’s also a great example of a deceptively simple method of assessing the value of a theory. A method that is hiding in plain sight. Namely, applying the theory to itself. If it can’t survive the encounter, then it’s probably not a very good theory.