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On Plantinga's Evolutionary argument against naturalism


1. Evolutionary Argument Against Naturalism
In Plantinga's Evolutionary Argument Against Naturalism (EAAN for short)[1][2], he attempts to show that to combine naturalism and evolution is self-defeating, because, under these assumptions, the probability that humans have reliable cognitive faculties is low or inscrutable. Plantinga defines:
N as naturalism.
E as the belief that we human beings have evolved in conformity with current evolutionary theory.
R as the proposition that our faculties are reliable.
Now for the argument that it is irrational to believe N&E: P(R/N&E) is either low or inscrutable; in either case (if you accept N&E) you have a defeater for R, and therefore for any other belief B you might hold; but B might be N&E itself; so one who accepts N&E has a defeater for N&E, a reason to doubt or be agnostic with respect to it.
2. On EAAN
But I have question on the statement: you have a defeater for R, and therefore for any other belief B you might hold. Is this statement true? I will argue that this statement is false. The reasons are as follows.
First, even you have a defeater for R, you can still have reliable beliefs, such as “The snow is white” or “1+1=2”, etc..
Second, we would like use the reliability of certain belief rather than the reliability of all beliefs in our daily life.
In the following of this paper, I would like to reconstruct the argument and reveal that EAAN is wrong.
N as naturalism.
E as the belief that we human beings have evolved in conformity with current evolutionary theory.
B as beliefs set. A as the set of all beliefs, including N, E, b1,b2….
R(B) as the reliability of the beliefs in B.
P(R({N,E})/N&E)=1 and P(R(A-{N,E})/N&E) is low or inscrutable.
Then P(R{N,E})=1 and P(R(A-{N,E})) is low or inscrutable.
There is no contradiction. Hence EAAN is wrong.
3. Conclusion
I am sympathetic with Plantinga’s intention, but EAAN is not a suitable method. In general, EAAN is a kind of arguments through artificial paradox, just like the proofs of God's existence or inexistence.
1. Plantinga "Naturalism Defeated" can be found at
2. An outline of a lecture Plantinga gave on his EAAN at BIOLA University can also be found at

On Plantinga's Evolutionary argument against naturalism

I share your doubts about EAAN in this aspect: "even you have a defeater for R, you can still have reliable beliefs, such as “The snow is white” or “1+1=2”, etc." 

My friend Dr Daniel. D. Novotný suggested the same in his paper "How to Save Naturalism from Plantinga" (published in Organon F). I recommend to ask him for an e-copy of the paper. His web:

(There's also a problem with the probability intervals Plantinga uses in EAAN. Which was pointed out in the collection of essays "Naturalism Defeated?" (including Plantinga's replies), and in the John Post's review of that collection.

Could I ask you for your paper or a draft (when you're done with them)?

On Plantinga's Evolutionary argument against naturalism
Chaohui Zhuang has (1) made a logical error and (2) missed the central point of Plantinga's argument.

On (1) Zhuang claims that "even you have a defeater for R, you can still have reliable beliefs, such as 'The snow is white' or '1+1=2', etc."

First, this begs the question by assuming that “The snow is white” or “1+1=2”, etc. are reliable beliefs. There is no doubt that the consensus of humans considers them unquestionably true and reliable, but that is not the point in dispute. The point in dispute is whether naturalism, and specifically evolutionary psychology, can justify that consensus. If our faculties are unreliable, we have no warrant to assume that anything produced by them is reliable. This would include both initial beliefs and the reflective beliefs that our initial beliefs are reliable. For example, an insane person could believe there are demons dancing on the bed and also reflectively hold the demon belief to be true and reliable; however, it does not follow that the demon belief is reliable. None of these beliefs is reliable because the faculty which produces them does not produce reliable beliefs.

Second, Plantinga does not claim to have a universal defeater for R, the proposition that our faculties are reliable. He claims he has a conditional defeater for R based on the assumption that naturalism is true. Thus, if there are in fact reliable beliefs, if does not follow that reliable beliefs are compatible with an unreliable faculty. It only follows that reliable beliefs are compatible with an unreliable faculty if naturalism is true. As the truth of naturalism is the very point in dispute, this is question begging.

Thus, Zhuang's first claim does not militate against Plantinga's Evolutionary Argument Against Naturalism (EAAN).

On (2) the central point of the EAAN is the reliability of our faculties, and reliability is not addressed by Zhuang's argument. Zhuang asserts that P(R({N,E})/N&E)=1, but does not justify his claim. The claim is false because N&E may be true incidentally without being reliably true. For a proposition to be reliable we must be able to justify it. To say it is reliable is not the same as saying it is true. First, some propositions, e.g. those of classical mechanics, may be fully relied upon if one knows their limitations, but that does not make them true because quantum and relativistic phenomena falsify them. Second, guessing may produce true propositions, but that does not make propositions arrived at by guessing reliable. To be reliable, a proposition must (a) be produced by a process that consistently produces true results (which guessing does not) and (2) consistently yields true consequences. "Consistently producing" does not mean infallibly producing. So, a process or faculty may be reliable without being infallibly producing true results. Plantinga has shown that evolution can produce responses which pass the test of natural selection without yielding true beliefs.

Accordingly, Chaohui Zhuang's critique fails on both of its points.

On Plantinga's Evolutionary argument against naturalism
Reply to Dennis Polis


Ad (1). I would rather say: even when you have a defeater for R, you can still know that 'The snow is white' or '1+1=2', etc." Similarly D. D. Novotný.
I'll leave here, due to my other commitments, only one relevant citation. It's from my previous conversation with Dr Tim McGrew, the author (with his wife Lydia) of "Internalism and Epistemology" (published in Routledge), a book criticizing relabilism about warrant.

I asked Tim: ".. there's a well-known skeptical problem, frequently raised by Plantinga (regularly quoting Reid, sometimes C. S. Lewis): it is absurd to defend,say, the veracity of intellectual grasping (against, say, the doubt of malevolent demon) by using intellectual grasping. It seems to me
that there is something wrong in this claim. But I am not clear about the nature of this flaw. Would you have some hints?"

Tim replied: "I think there are some kinds of intellectual grasping that are demon-proof. The skeptical objections that have the greatest plausibility are directed, in the first instance, not against these things but against more mundane beliefs. Here is a passage from the Introduction of our recent book that speaks to this sort of criticism:

It becomes, at this point, an urgent question whether internalists have the resources to escape from the regress that catches the externalist. In view of the way that the metaregress argument is set up, this hinges on the question of whether the internalist’s epistemic principles satisfy the modal principle; and this in turn depends on the nature of a priori knowledge. In the fifth chapter we stake out a modest claim, arguing merely that some a priori knowledge is analytic and that the epistemic principles needed by the internalist are of this sort. More daringly, we argue that a refined and expanded version of Locke’s doctrine of intuition is correct: there are occasions on which we are infallible in our beliefs, and some of our beliefs about the interconnections of our concepts are cases of that sort. The combination of an analytic a priori account of epistemic principles and an intuitional account of foundations of analytic a priori knowledge suffices to secure the internalist against the metaregress.
Externalists will surely retort that the security is purchased with Scheingeld. It is a philosophical commonplace that any position of the Lockean sort is open to two devastating objections: that it is inconsistent with human fallibility, and that we could never know for sure whether we were really “grasping” the relations of our concepts or were merely seeming to grasp them. The former problem seems to rule out the sort of certainty promised by the internalist; the latter prevents him from taking any philosophical satisfaction from such certainty even if it exists.
Both objections, we argue, are mistaken. One may hold without inconsistency both that humans are frequently prone to fail and that there are some sorts of knowledge that are infallible. From the fact that we sometimes fail we may justly infer that we are sometimes not infallible, but it does not follow that we are not sometimes infallible. The latter objection involves a similar illicit inference. Certainly we sometimes have doubts about necessary truths – who can deny this? But it does not follow that we can never have a grasp of any necessary truths that leaves no room for doubt.

In the nature of the case, one does not *argue* for such grasp; one does one's best rather to show the skeptic what it is like to have such a grasp, even to *induce* it in him. If that fails, rational discussion is at an end."

I agree with Tim, and I would not take it as "begging the question." I really recommend the book, it makes much sense (in contrast to many other books on epistemology, IMO), but it is not mere common sense.

On Plantinga's Evolutionary argument against naturalism

Thanks for all the responses. There is a close relation between this problem and the definition of knowledge.  In my opinion, there are different kinds of knowledge.

Dear Vlastimil Vohánka, thanks for your information.
My post is just a draft.

On Plantinga's Evolutionary argument against naturalism
Where Plantinga's argument fails is that he confuses beliefs with belief-producing mechanisms. His main argument is that evolution selects mechanisms that produce beliefs that are adaptive (favour survival), and that that does not entail that such mechanisms produce reliable beliefs.
He then produces an example of a belief that is adaptive but not true, involving an example with a primitive man and a tiger. He argues that there are many more adaptive untrue beliefs than adaptive true ones, so it is more probable that any given adaptive belief is untrue than true.

He presents that (entirely reasonable) conclusion as if it is equivalent to there being many more adaptive unreliable belief-producing mechanisms than adaptive reliable belief-producing mechanisms, but makes no argument for this equivalence (and there are good reasons to suppose the equivalence is false. For a start I have never seen a single proposed adaptive, unreliable belief-producing mechanism, and Plantinga doesn't produce one). But he needs that equivalence to justify his assertion about the probability of our belief producing mechanisms being reliable.

There is another arm of his argument that relates to the possibility that all of our sensory inputs are illusions. That also has counter-arguments, including Occam's Razor, but as he is unable to estimate the likelihood of our sensory inputs being illusions, it doesn't matter given that the argument for the other arm fails as shown above.