Plantinga's Evolutionary Argument against Naturalism (Atheism)

Plantinga's Evolutionary Argument against Naturalism

For our purposes, we will dispense with detailed terminology and simply use the word “Atheism” to describe someone who rejects the existence of God, souls, ghosts, demons, spirits or anything supernatural. For us, an atheist is a person who thinks the physical is all that exists. Therefore, Plantinga's argument is simply a claim that you cannot rationally believe in both atheism and evolution. It works like this.

We typically think our actions are caused by a causal chain like this.

Beliefs held by a rational soul ->causes-> long standing electrochemical events in the brain (neural states) ->causes - > bodily movements (behaviors)

But on atheism the causal chain is very different.

Neural States - > Behavior

Same Neural States - > Beliefs (content property for the neural state)

The key is that the neural state causes both the belief and the action in the atheist's view.  In the traditional view a soul causes beliefs which then cause neural states which cause actions.  Please make sure you understand this distinction before reading further.

A key point is that the content properties of the neural state and the behavior causing properties of the neural state are different things. If I say I want a ham sandwich, then I have expressed a sentence in English. But that sentence also possesses content. If a woman says the same thing in Chinese, then she will form a very different collection of sounds, but the content is the same.

Thus the point is that neural states are the independent cause of both behavior and a secondary content for those neural states, beliefs. There simply is no reason why the beliefs caused by those neural states should correlate to reality. We typically think that incorrect beliefs will lead to incorrect behavior. Thus failure would result in a change to the beliefs. But on atheism, the beliefs are not causing behavior. They are a secondary byproduct. If we imagine that a Zebra sees a lion, then this causes a neural state in the zebra. To survive, the zebra must move. Thus a neural state that doesn't lead to survival of the zebra would not be beneficial to reproduction. Therefore evolutionary theory provides a good explanation for why a neural state that didn't correctly cause survival behaviors would be unlikely to exist. Frogs know how to catch flies. A mouse in a maze knows how to find cheese. But the content also caused by these neural states need not correlate to reality.

The zebra, frog, and mouse must all possess neural states which are sufficient to cause survival enhancing behavior. So the zebra must have indicators of the presence of the lion. But an indicator of the lion's presence is not the same as a belief, which would be a content property associated with the neural state. For example, if you eat an entire cake, then your body has indicators of raised blood sugar and responds accordingly. But you need not have any beliefs associated with this.

It may seem rather obvious that neural states which cause correct behavior will also cause an associated belief content that correctly correlates to reality. But this isn't the case. One way to think of this is to imagine what would happen. Let's say that a neural state does in fact cause true beliefs. But somewhere along the way, it changes a bit and starts causing incorrect beliefs. Thus we have to ask, what would ever correct the false beliefs? The beliefs caused by the neural states could vary wildly. Like a sentence that can be expressed in multiple languages, it wouldn't matter what beliefs get associated with the neural states as long as those states cause correct behavior as well. The issue is that the beliefs are outside of the causal chain. We could literally be living in an illusory world full of beliefs that are nothing more than a secondary byproduct of our neural states. The important thing to understand is really the basic concept that content properties associated with words or with neural states are not the same thing as the words or neural states. Language can change. Meanings of words can change. And since the atheistic view is that neural states cause behaviors directly, then the content is a byproduct and causes no behaviors.

Therefore, according to the principle of indifference, we have to assign the trustworthiness of our beliefs a chance of 50-50 or ½. We have no way to swing the bar either way.

The next serious question is whether our beliefs are likely to be trustworthy or not. Calculating probability is greatly affected by the complexity of combinations vs probabilities that ignore combinations. For example, let's say you only hold 4 beliefs. What are the odds that one of them is false? That's a one in four chance. So let's say you hold 1000 beliefs. The odds that one in four are false would be, you guessed it, one in four.

But it gets more complicated. Most of the beliefs we hold are combinations of beliefs. Only basic beliefs are not. So the way the possibilities combine is relevant. For example, a license plate that reads “HP3192” is not the same as one that reads “P3192H” even though all of the same letters and numbers are present. With only 26 letters and numerals, there are over two billion possible permutations. It is with this method of different combinations(technically permutations) that the human brain can become so complex. Each neuron in the brain connects to 7000 others. Thus there are more possible configurations than there are electrons in the entire universe.

Specifically for us, in the case of evolutionary theory, many of the beliefs held represent combinations of other beliefs. Inferences and inductions are made based on experiment and evidence. It would be a truly enormous task to layout all of the epistemological structure of the grand theory of evolution. But It is different combinations of beliefs that form the theory of evolution. If they are combined in different ways, then we arrive at a very different theory. Let's say that for our beliefs to be generally reliable, we must have 3 true for every four false. So if it took four beliefs, there is a 5/16 chance that 75% are trustworthy. In other words, there are 5 possible ways that 75% can be true. We can do a very modest assessment of 100 beliefs that combine to form the outcome. The total number of possible permutations is 2^100 = 1.26x10^30. The possible ways 75% can be true is calculated a bit differently. Let's say that any false belief is as false as another. Then there are 100 possible locations for the first one, 99 locations for the second one, 98 for the third, and so on. This would be done until 75 since we are only asking how many ways the 25 false beliefs can be permuted. Of course we would also want to know how many ways 24 false beliefs can be permuted, 23, 22, and so on. Simply trusting Plantinga's calculations, then the possibilities are .001 that at least 75% of the beliefs leading to the theory of evolution are reliable.

Therefore, atheism and evolution, when combined together, provide a contradiction. In other words, this is a belief that cannot rationally be affirmed, since believing it means that you must also not believe it.

Plantinga has only first proposed this argument in 1993 and reformulated it in 2008. In philosophy, that's pretty new. Let's take a look at possible refutations. One objects to the principle of indifference. It says that if we don't know what an outcome will be, then we can't give it a probability of 50/50. It seems obvious to me, though, that this is a perfectly reasonable mathematical description of, “I don't know what will happen.”

The other objection I will consider goes back to the basic idea. This is called the distinction between methodological materialism and metaphysical materialism. We considered the idea that neural states cause behaviors as well as beliefs alongside these behaviors. But metaphysical materialism says that the neural states simply are identical with the beliefs. It seems obvious to me that this isn't much of an objection though. Simply put, if those neural states both cause beliefs and are themselves beliefs, it would be just a mere accident that the belief content properties of those neural states just so happen to correlate to reality. The electrochemical properties and the content properties are just different things. The neural state would be sufficient to cause the behavior. And it would be a statement that represents content also. But it would just be a lucky happenstance if this content correlated to reality. So the odds are still 50/50. Honestly it seems like Plantinga's objectors are simply grasping at straws here.

Therefore it seems painfully obvious that atheism and evolution taken together are self defeating. You can be an atheist who believes human thought arises in some other manner. Or you can believe in theism and evolution. But you can't have both.

“But then with me the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?
[To William Graham 3 July 1881]”