Alvin Plantinga, a seasoned philosopher of religion and critic of atheistic and naturalistic belief, develops the following thesis in his 2011 work Where the Conflict Really Lies: "there is superficial conflict but deep concord between science and theistic religion, but superficial concord and deep conflict between science and naturalism." In essence, Plantinga argues that the enterprise of science functions better given certain theistic assumptions than it does given certain natrualistic assumptions. Such a claim is a direct assault on the naturalist's stronghold, for the core of naturalist doctrine is powered almost exclusively by the authority of science. Plantinga, of course, is well-aware how close to the artery his argument cuts: He colorfully writes, "Naturalists pledge allegiance to science; they nail their banner to the mast of science; they wrap themselves in the mantle of science like a politician in the flag" (p. 307). Certainly, if naturalists are as wedded to science as Plantinga takes them to be, and if Plantinga's central thesis is remotely successful, then naturalists have something of a crisis on their hands.
Plantinga systematically develops each of the major claims in his thesis throughout the book. He begins by discussing how the alleged conflict between science and theism is merely superficial, goes on to argue that science and theism are deeply concordant, then claims the concord often attributed to science and naturalism is actually superficial, then finally argues that science and naturalism are in deep conflict. Although each of these discussions is substantive, interesting, and, in characteristic Plantinga style, entertaining, I will only discuss the argument I found most interesting--the argument that science and naturalism are in deep conflict--and encourage the reader to pick up the book him or herself to learn more about the others.
The argument asserting that naturalism and science are in deep conflict follows from an argument called the Evolutionary Argument Against Naturalism (or EAAN). Here I will provide a brief summary of the argument then discuss it in more detail.
EAAN claims that there is an incompatibility between beliefs in
naturalism, unguided Darwinian evolution, and the reliability of human cognitive
faculties. The argument supposes that if naturalism and
unguided Darwinian evolution are both true, the probability that human
cognitive faculties are reliable is low--this is so because the Darwinian process only selects for adaptive behaviors, not for true beliefs. If this is granted, then the beliefs that naturalism and Darwinian evolution are both true lead one to believe that his or her own rational judgments are everywhere compromised, which of course includes the very judgments that naturalism and Darwinian evolution are both true. Thus, the EAAN asserts that naturalism and evolution undermine or defeat the belief that human cognitive faculties are generally reliable. Assuming that the EAAN successfully demonstrates that naturalism and evolution make cognitive faculties generally unreliable, Plantinga then points out that the enterprise of scientific inquiry crucially depends on the general reliability of human cognitive faculties, and thus the EAAN indicates that there is deep conflict between belief in naturalism, evolution, and the practice of science.
Now, the terms employed in the EAAN are prone to confusion, so let me say a few clarifying remarks about them.
First, "naturalism" in Plantinga's sense bears two important characteristics: it asserts a) that there exists no God or anything like God, and b) that human beings are material objects and therefore subsumed under the (theoretically complete) laws of physics. With respect to (a), much could be said about what features of God naturalists typically reject, but that is probably unnecessary: suffice it to say that all naturalists are atheists conventionally understood. With respect to (b), some naturalists may reject a wholesale materialism (which is the view that nothing other than material objects exist), but Plantinga only means to take naturalism to include materialism about human persons. This means that human beings do not have immaterial minds or souls that reach into the physical world and cause physical effects. This feature of naturalism is vital for understanding why the EAAN asserts that adaptive behavior is conceptually distinct from true belief. Plantinga's version of naturalism, then, takes human beings to be caught in a world of determinate physical causes and effects just like any other physical object is so caught. Whatever physical actions human bodies undertake, they are entirely explainable by the determinate laws of physics.
Second, "unguided Darwinian evolution" is meant to include the familiar processes of random genetic mutations filtered by natural selection. I've included the term "unguided" to make it clear that Plantinga wishes to discuss the version of Darwinian evolution that excludes the possibility that God uses the Darwinian mechanisms as an instrument to achieve His ends. Thus, Darwinian evolution means exactly what the naturalists take it to mean: a blind, unguided, undirected, purposeless series of purely physical events that just-so-happened to have manifested the variety of creatures in existence today. No intelligent guidance participated in this process. Hereafter, every use of the term "evolution" in this essay means "unguided Darwinian evolution."
Third, the term "cognitive faculties" refers to the suite of nervous system functions that are generally associated with belief-formation. This includes the brain and spinal cord, along with processes like memory, perception, and inference. These cognitive faculties are considered reliable if they happen to produce more true beliefs than false beliefs. For the sake of discussion, Plantinga loosely approximates reliable cognitive faculties to, on average, produce at least two true beliefs for every one false belief--i.e., human cognitive faculties are reliable if the average human's store of beliefs is filled at least two-thirds full of true beliefs.
With these terms in place, I will state the EAAN somewhat formally, as Plantinga does (pp.344-345):
Premise 1: Given that naturalism and evolution are true, the probability that human cognitive faculties are reliable is low.
Premise 2: Anyone who believes naturalism and evolution and sees that, given those beliefs, the probability that human cognitive faculties are reliable is low has a defeater for believing that human cognitive faculties are reliable.
Premise 3: Anyone who has a defeater for believing human cognitive faculties are reliable has a defeater for any other belief she thinks she has, including naturalism and evolution themselves.
Premise 4: If one who accepts naturalism and evolution thereby acquires a defeater for naturalism and evolution, naturalism and evolution are self-defeating and can't be rationally accepted.
Conclusion: Naturalism and evolution can't be rationally accepted.
Notice that the conclusion of the argument is NOT that naturalism and evolution are false; rather, the conclusion is that they cannot rationally be accepted. The argument centers on the reliability of human cognitive faculties, not on the truth of naturalism and evolution. If human cognitive faculties fail to produce reliably true beliefs, then really anything could be true--we just wouldn't have any idea which propositions are true. This point nevertheless provides little comfort for the naturalist: generally, naturalists are interested in knowing certain truths about the world, like that God does not exist or that science is a source of knowledge. If the EAAN is successful, the naturalist would have to abandon most of his confidence in his own knowledge of the world, including the beliefs that God does not exist and that science is a truth-producing enterprise. But, if belief in naturalism and evolution forces one to abandon the veracity of science, there is indeed a deep conflict between naturalism, evolution, and science. For this reason, Plantinga's EAAN is a serious threat to naturalism.
Now, it seems to me that premise (1) is the crucial premise. An advocate of naturalism and evolution is not likely going to concede that natural selection is "blind" to belief content, or that evolution is incapable of producing belief-forming mechanisms that are reliable. Thus, I will substantiate premise (1) a bit more.
Recall that Darwinian evolution involves two principle processes: random genetic mutations and natural selection. Since we're assuming that naturalism is true, genetic mutations are "random" in the sense that they are not directed toward any purpose or for any reason. They are random in the way the outcome of a roll of dice is random. Over many generations of organisms, some random configurations of body parts prove to endure better in certain environments than others, and thus the ones that endure reproduce more often, preserving their particular genetic configurations. The mechanism that filters the "successful" random variants from the "unsuccessful" is natural selection. Again, since we're assuming naturalism is true, none of these organisms have immaterial "minds" or "souls" that causally affect the physical motions of their bodies. All natural selection can detect, therefore, is physical behavior--the movement of body parts from one moment to the next. Furthermore, the only causal powers that can affect the movement of body parts from one moment to the next are physical forces, like electromagnetism, gravity, and nuclear forces. Thus, Darwinian evolution only has the resources to preserve organisms that are configured to convert purely physical inputs into successful varieties of purely physical outputs. In other words, Darwinian evolution selects for adaptive behaviors, where behaviors are fully caused by antecedent physical forces.
Given that naturalism and evolution are both true, in what way would the beliefs of, say, humans have anything to do with their getting their body parts to move around in such a way that they stay alive and keep reproducing? Since we're taking naturalism to include materialism about human beings, human beings do not have immaterial minds that causally affect the motions of their bodies. Smith's body did not go to the fridge and grab a beer because he had some immaterial mind that both believed there was a beer in there and caused his body to move to the fridge. Instead, some combination of physical forces acting on the material components of Smith's body--all of which may or may not have beliefs about anything, much less beer or refrigerators--wholly and exclusively brought about the motions of Smith's body to the fridge. Whether or not Smith (or Smith's brain, or Smith's cerebral cortex, etc.) had any beliefs about beer, refrigerators, or, for that matter, unicorns, is of no material consequence to the physical sequence of events. As far as evolution is concerned, then, beliefs are invisible to the natural selection mechanism.
Premise (1) now follows from this state of affairs: If beliefs are invisible to natural selection, then natural selection cannot separate nervous systems that produce true beliefs from nervous systems that produce false beliefs. Furthermore, if natural selection cannot separate nervous systems based on true versus false beliefs--and we're assuming naturalism and materialism about human beings--then nothing has calibrated human cognitive faculties to produce true beliefs rather than false beliefs. At best, we can only say that human cognitive faculties are as likely to produce true beliefs as false beliefs, which means that the probability that any given human belief is true is about 0.5. The sum total of any human's beliefs then will fall quite a ways short of meeting Plantinga's earlier criteria for reliability--that roughly two out of every three beliefs is true.1 If this analysis is correct, then premise (1) appears to be substantiated: Given that naturalism and evolution are both true, the probability that human cognitive faculties are reliable is low (less than two out of every three beliefs will be true).
Now, how might one attack premise (1)? An obvious move would be to assert that natural selection and evolution, in fact, do favor the creation of reliable human cognitive faculties. The philosopher Stephen Law has made such a move (see his paper "Evolution, Naturalism, and True Belief", Analysis, Jan. 2012). Law writes in the paper, "Plantinga overlooks the fact that adherents of naturalism may hold, seemingly
quite plausibly, that there exist certain conceptual links between belief
content and behaviour." In his conclusion, Law states, "It seems intuitively obvious to many of us that
belief content is not entirely conceptually independent of behavioural output:
that one cannot plug any old belief content into any old neural structure (or
soul-stuff structure, or whatever) entirely independently of its behavioural
output." Law seems quite right to suggest that, intuitively, we do not suppose that behaviors are conceptually independent of each other--that is, we do not suppose that combinations of beliefs and behaviors are essentially random. Instead, we easily recognize that, for example, Smith's going to the fridge and grabbing a beer is conceptually associated with Smith's believing there is a beer in there. Given this obvious, intuitive fact about beliefs and behaviors, Law claims Plantinga is wrong to suppose that beliefs arise independently of behaviors.
It seems to me, though, that Law's argument fails to appreciate the extent to which the tenets of naturalism influence Plantinga's argument. Plantinga makes it clear in chapter ten that, "The question is what things would be like if [naturalism and evolution] were true; and in this context we can't just assume, of course, that if [naturalism and evolution], [naturalism] including materialism, were true, then things would still be the way they are" (p.336).
The "intuition" that Law appeals to appears to derive from the way things are, rather than the way things would be if naturalism were true. This is to say, if naturalism were true, the world would not necessarily be the way it appears to us now, and so whatever intuition Law has about the world as it is now would not necessarily apply in a world where naturalism were true. Law does attempt to avoid this problem by writing this in his paper: "That intuition would appear to be, philosophically speaking, largely
pre-theoretical. It cannot easily be dismissed by Plantinga as a product of
some prior theoretical bias towards naturalism and/or materialism."
By "pre-theoretical," I take Law to mean that his intuition about the conceptual links between beliefs and behaviors is simply a given in any metaphysical system, regardless of the stipulations of that system. This strikes me as quite an odd assertion; it appears to want to get these needed conceptual links for "free," which is to say, it wants naturalism to come pre-loaded with them rather than have them derived from the naturalist metaphysics itself. Given the structure of Plantinga's version of the EAAN though, I see no good reason why Law's maneuver here should be granted. Law's line of argument needs to show why, given a world where naturalism and evolution are true, conceptual links should develop between beliefs and behaviors in that world. So far as I can tell, then, Law's objection is incomplete.
Unless there are versions of Law's argument or other arguments I have yet to read that do show how naturalism and evolution, on their own terms, can generate reliable human cognitive faculties, it seems to me that Plantinga's EAAN successfully spoils the relationship between naturalism and science. We might say now that Plantinga has placed naturalists in a severely distressing dilemma: naturalists must either choose to abandon their allegiance to naturalism, or they must choose to abandon their allegiance to science. As it stands, the EAAN uncomfortably catches naturalists between a rock and a hard place.
Overall, then, my response to Plantinga's effort is highly favorable. Plantinga delivers a trenchant, timely, and interesting discussion of a highly contentious topic. Fans of philosophy--the debate between theism and naturalism especially--should find this work a quintessential piece of analytic philosophy. Theists should find the book a challenging but pleasurable read; naturalists should find the book a challenging but necessary read.
1. For example, if we assume each independent belief has a 0.5 probability
of being true, then if a human has 9 independent beliefs, the
probability that at least 6 if them are true is about 0.25; if a human
has 60 independent beliefs, the probability that at least 40 of them are
true is about 0.0067; if a human has 100 independent beliefs, the
probability that at least 66 of them are true is about 0.000895--in
general, the more independent beliefs one has, the less likely it is
that two-thirds of them will be true.
I performed these calculations using a binomial probability distribution function:
f(x) = nCx(p)x(1-p)n-x
where n = number of beliefs, x = number of true beliefs, and p = probability that any given belief is true, and nCx is the binomial coefficient computed n! / [x!(n - x)!]
For example, if we assume that an individual has 9 independent beliefs, that the probability any one of them is true is 0.5, and we want to know the probability that at least 6 of them are true, we let n = 9, p = 0.5, and sum the values of the equations when x = 6, 7, 8, and 9 (which means we want to know the total probability that the person has either 6, 7, 8, or 9 true beliefs--i.e., the probability that at least 2/3 of the beliefs are true), we would compute as follows:
f(x) = 9C6(0.5)6(1-0.5)9-6 + 9C7(0.5)7(1-0.5)9-7 + 9C8(0.5)8(1-0.5)9-8 + 9C9(0.5)9(1-0.5)9-9 = 0.164 + 0.070 + 0.018 + 0.002 = 0.254, or about 0.25
Thus, the probability that 2/3 or more of one's beliefs are true, provided one has 9 independent beliefs and each belief has probability 0.5 of being true, is 0.25, or 25%.↩