By Cynthia R. Nielsen
The following is taken from a transcription of a lecture given by Alvin Plantinga. I have at times summarized his points, but for the most part the content is his. I have also uploaded the full transcription, which you can obtain here. If you want to hear the lecture for yourself, click here.
As I understand Plantinga’s argument against evolutionary naturalism, he is not directing his argument against the theory of evolution itself, but rather against the problems that arise for the materialistic atheist due his/her belief in the conjunction of naturalism and evolution, viz., the position becomes self-referentially incoherent because a defeater can be established that shows that on such a position our cognitive faculties are unreliable and hence all of our beliefs are as well (including the belief in naturalism and evolution).
Plantinga opens his lecture by stating that there is a surface disagreement between science and theism, but in truth a deep concord between the two. He also adds that there is a surface agreement between naturalism and science, but in truth a deep discord between the two.
Plantinga’s lecture centers on our cognitive faculties-the faculties whereby we have knowledge and form beliefs. According to Plantinga, it is natural from a theistic point of view to think that our cognitive faculties are reliable. That is, they give us for the most part true beliefs when they are functioning properly and are in the right sort of setting-when they are in the cognitive environment for which they were designed. Plantinga thinks, however, that for the naturalist there is problem as to whether our cognitive faculties are reliable. He argues that the naturalist has a defeater for the idea that our faculties are reliable, and that this gives him a defeater for everything that he believes, including then, the belief in evolution and naturalism. Thus, the basic structure of Plantinga’s talk is that evolutionary naturalism, the idea that evolution and naturalism are both true, is self-referentially incoherent. If you think that the proposition, “N&E” [naturalism and evolution are true], then Plantinga will attempt to show that there is a very good reason to doubt it and give up this belief.
Contra certain optimistic claims by folks like Richard Dawkins, Plantinga believes that there is a problem for the naturalist, at least the naturalist who thinks that we and our cognitive faculties have arrived on the scene after some billions of years of evolution basically by way of natural selection working on random genetic mutation. As the story goes, Richard Dawkins, according to Peter Medawar, once leaned over to the philosopher A.J. Ayer, at one of those fancy Oxford candlelight dinners and said that he couldn’t imagine being an atheist before 1859, which was the year when Darwin’s Origin of Species was published. Dawkins went on to say, “although atheism might have been logically tenable before 1859 [before Darwin], Darwin made is possible to be an intellectually fulfilled atheist.”
Contra Dawkins claim that Darwin made is possible to be an intellectually fulfilled atheist, Plantinga argues Dawkins is dead wrong here and that the truth lies in the opposite direction. In fact, Plantinga’s argument suggests that is not possible to be an intellectually fulfilled atheist or naturalist. The reason that Darwinism doesn’t allow this to be possible is that according to naturalistic evolution, the function or purpose of our cognitive faculties, is not that of producing in us true beliefs, but of promoting fitness, promoting survival, promoting survival through reproduction and reproductive fitness. If our cognitive faculties just happen to produce true beliefs that really doesn’t matter. Rather, what counts for that perspective is what role they play in maximizing fitness. Plantinga turns to Patricia Churchland, a natural philosopher of science, who writes on evolution and such topics. According to Churchland, “a nervous system allows the organisms to succeed in the four ‘f’s’: feeding, fleeing, fighting, and reproducing.” Churchland continues, “the principle chore of nervous systems [that is, a brain, for example, and the rest of one's nervous system] is to get the body parts where they should be in order that an organism survive.” So the brain and cognitive faculties serve to get the body parts in such a place that the organism may survive. Then Churchland adds, “Improvements in [...] motor control confer an evolutionary advantage, [...] representing is advantageous so long as it is geared to the organism’s way of life and enhances the organism’s chances of survival. Truth, whatever that is, definitely takes the hindmost.” Her point is that from the perspective of evolutionary naturalism, what counts is one’s behavior-this is what evolution is interested in-it rewards adaptive behavior and penalizes maladaptive behavior, but it doesn’t care a bit about belief. If all of your beliefs are ludicrously false, but your behavior is appropriate, then you will survive and reproductive. On the other hand, if all of your beliefs are true, but your behavior doesn’t conduce to fitness, you won’t survive and reproduce. What natural selection is interested in is not true beliefs or reliable cognitive faculties, but faculties and beliefs that contribute to survival.
As Plantinga points out, Darwin himself saw the problem that Plantinga will highlight. Darwin himself wrote in a letter to a friend, “with me the horror always arises whether the convictions of man’s mind, which has been developed from the mind of 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?” So Darwin has this doubt [Plantinga refers to this as "Darwin's doubt"], that is, given the origin of ourselves and our cognitive faculties, there is a real question as to whether our cognitive faculties can be reliable or trustworthy.
Plantinga presents both a simplified and a complex version of his argument. The simplified version is as follows. If you are a naturalist, you will also be a materialist. You will think that human beings are material objects-they do not have an immaterial soul, self or ego. You will also think that your beliefs are caused by processes in your body, in particular, by neuro-physiological processes. So neuro-physiology causes belief. It is also neuro-physiology that causes behavior. Electrical impulses are sent down through different nerves to the muscles. The muscles contract and the result is action and hence behavior. Thus, neuro-physiology causes both belief and behavior. Now we can assume with respect to these creatures that their behavior is adaptive and hence that their neuro-physiology is adaptive in the sense that it causes adaptive behavior and belief.
Now what is the likelihood that a given belief is true, given that it is produced by neuro-physiology that causes adaptive behavior? If you think about it, it really doesn’t matter whether it is true. Rather, what matters for survival and for fitness is that the neuro-physiology causes the right kind of behavior. It can cause whatever kind of belief it wants to as far as natural selection is concerned. So from the fact that the behavior is adaptive, nothing follows so far about the likelihood that a given belief is true. So what is the likelihood then that a given belief is true on the part of these creatures? Given the information that we have, which is just N&E [the conjunction of naturalism and evolution], the probability is .5-50% true and 50% false. So you have no more reason to think it true, than to think it false. But if that is true for each individual belief, then the probability that a whole set of beliefs are true or mostly true, which would be required by cognitive reliability-by the idea that cognitive faculties are reliable-the probability is going to be very small. Suppose that you have one hundred independent, logically and probabilistically independent beliefs. The probability with respect to each one of them that each would be true is .5. Then the probability that three-fourths of them would be true will be very small (one out of ten thousand or so). Hence, the probability of the reliability of our cognitive faculties given the conjunction of naturalism and evolution P(R/N&E) is low.
In Plantinga’s more complex version of the argument (which I won’t spell out here-download the transcript if you are interested in the details), he highlights four different possibilities as to how belief and behavior could be related (including (1) epiphenomenalism, (2) semantic epiphenomenalism, and (4) the idea that our beliefs cause behavior both by way of content and by way of neuro-physiology and are adaptive).[1] On the first two possibilities (1) epiphenomenalism and (2) semantic epiphenomenalism, P(R/N&E) is low and on the fourth the P(R/N&E) is .5 or perhaps somewhat better. If you put these all together (and there is a formula for doing so from which he spares us), the P(R/N&E) will be fairly low. So it seems something like this reasoning regarding the reliability of our cognitive faculties [P(R/N&E) is low] is similar to what conflicted Darwin.
What Plantinga argues next is that if we accept N&E, then we have a defeater for R [=reliability of our cognitive faculties]. Thus, anyone who believes N&E has a defeater for R. The conclusion of Plantinga’s argument then is that it is irrational to believe N&E, as the probability of R/N&E is low. That means that if you accept N&E, then you have a defeater for R [=the proposition that our cognitive faculties are reliability]. But if you have a defeater for that belief, then you have a defeater for any belief that is a product of your cognitive faculties, and of course, that is all of your beliefs. One of those beliefs is of course N&E itself [that naturalism and evolution are true]. So you have a defeater for N&E itself. Consequently, one who accepts N&E has a defeater for N&E-a reason to doubt it or to be agnostic about it. If s/he has no independent evidence for it, then the rational position would be to reject belief in N&E. Therefore, N&E in the absence of independent evidence for reliability-(and he argues elsewhere that you can’t really get independent evidence for your own reliability)-in the absence of that N&E is self-defeating, and hence, irrational. It is self-referentially incoherent.
Consequently, one who is contemplating naturalism and is torn between naturalism and theism should reason as follows: if I were to accept naturalism (and here naturalism includes evolution, N&E), I would have good and ultimately un-defeatable reasons to be agnostic about naturalism, so I shouldn’t accept it. So what we have is an argument not for the falsehood of naturalism, but for the irrationality of believing it. The traditional theist, on the other hand, has no corresponding reason for doubting that it is the purpose of our cognitive systems to produce true beliefs, nor a reason for thinking that the probability of a belief’s being true given that it is a product of our cognitive faculties is low or inscrutable. She may indeed endorse some form of evolution, but if she does it will be a form of evolution guided and orchestrated by God. And qua traditional Jewish, Christian and Muslim theists, she believes that God is the premier knower and has created human beings in his image.
Notes
[1] The third option is not discussed because it is not taken seriously.