Alvin Plantinga’s Evolutionary Argument Against Naturalism

By Madison Ruppert: If you’re a naturalist who holds to evolution, you probably think your worldview is quite rational. Eminent philosopher Alvin Plantinga, however, would say that your system of beliefs defeats itself and is thus irrational. Plantinga, who spent most of his career at the University of Notre Dame and Calvin College, developed the “Evolutionary Argument Against Naturalism” to show just how irrational it really is.
There are a few things that must be noted in order to understand Plantinga’s argument. First, this isn’t an argument against evolution. It also isn’t an argument against naturalism, per se. Instead, it just shows that it is irrational to hold naturalism and evolution together and continue to say that naturalism is, in fact, true.
Some definitions are also important. By evolution, he means natural selection acting on random mutation. He defines naturalism in the simplest way possible, essentially that there is no such person as God or anything like a god.
Plantinga points out that naturalism is a step beyond atheism. Not all atheists are naturalists, though all naturalists are atheists.
So what is his argument?
Well, it would be best summarized by Plantinga himself:

The above is a relatively crude outline of the argument, but it gives the gist of the line of reasoning.
For those wanting a more in-depth treatment, you can read an outline from one of his talks on the argument here or even better, watch his talk delivered at the University of Southern California below:

In the latest formulation of the argument, Plantinga narrowed his focus somewhat. In the 2008 formulation, which differs slightly from the 1993 version, he focuses on “semantic epiphenomenalism.”
Semantic epiphenomenalism is, essentially, the contention that beliefs indeed have a causative link to behavior – which is what natural selection would select for – but not because of the semantic content of the beliefs.
Instead, according to semantic epiphenomenalism, the belief is essentially a long-term neuronal event. This is what most materialists hold.
On this view, a belief has two kinds of properties:

1. Neurophysiological (NP) properties , which could also be called electro-chemical properties
2. Content properties (content being the belief that p for some property p)

Given unguided evolution, we would say that the NP properties came to be via tiny increments over millions of years. But the origin of the content property of the belief is not as easily nailed down.
Plantinga points to two major arguments offered by materialists for how this comes to be.

1. Content properties are reducible to NP properties
2. Content properties supervene upon NP properties (that is to say that the properties at the lower level determine the properties at a higher level)

Both positions are very similar since both are reductionistic and if content properties are reducible to NP properties, content properties also supervene upon NP properties.
According to Plantinga, at a certain level of complexity of neuronal structures (what level of complexity is not certain), content appears.
It doesn’t matter if the content properties are reducible to NP properties or if they supervene upon them, Plantinga argues. Either way, at a certain level of complexity, content is acquired and it becomes a belief.
Thus, given naturalism, what is the likelihood that the content that arises is actually true? Plantinga argues that it is very low.
Plantinga argues that the conditional probability of the reliability of our cognitive faculties given naturalism and evolution is low. After all, naturalistic evolution selects only for adaptive behaviors, not for adaptive content. It might select for adaptive NP properties, but it does not care about the content properties, as long as the content properties produce advantageous behaviors.
Thus, we have little to no reason to believe in the probability of our minds being reliable. All we know is that they have produced advantageous behaviors, if both naturalism and evolution are true.
The problem that arises is quite obvious: if we have no reason to believe in the reliability of our cognitive faculties, we have created a defeater for all of our beliefs. That defeater would also obviously apply to naturalism, since that is one of the beliefs produced by our cognitive faculties.
Thus, for someone to hold to naturalism and evolution and say that their belief in naturalism is true, one is being internally inconsistent. To phrase it with a bit more jargon, the conjunction of naturalism and evolution is self-referentially incoherent.
If that confuses you, let me attempt to phrase it in the most simple way I can (with the risk of over-simplifying it and weakening the argument):

1. Naturalistic evolution does not select for true beliefs, only advantageous behaviors
2. If naturalistic evolution is true, we have no reason to think that most of our beliefs are true, and therefore that our cognitive faculties are reliable
3. If we have no reason to believe that our cognitive faculties are reliable, we have no reason to believe that beliefs produced by our cognitive faculties are probably true. Instead, we have reason to believe that they are probably false
4. A belief in naturalism is produced by our cognitive faculties, thus we have no reason to believe that naturalism is true

Again, that is a crude over-simplification and could very well be misrepresenting the argument by trying to whittle it down too much. If you want to actually understand the argument, please watch Plantinga’s talk above or read some of his works on the subject including Knowledge of God, Warrant and Proper Function and Naturalism Defeated?: Essays on Plantinga’s Evolutionary Argument against Naturalism (which contains a final essay by Plantinga defending his argument). Also of interest may be his latest work, Where the Conflict Really Lies: Science, Religion, and Naturalism.

Source