Alvin Plantinga's formulation of the argument is here. I'll try to summarize it as I understand it.

  1. Naturalistic evolution selects for traits that tend to lead to survival.
  2. Some true beliefs about the natural world lead to survival.
  3. Some false beliefs can also lead to survival if those beliefs lead to behavior that promotes survival.
  4. The probability of a given survival-promoting belief being true is low or inscrutable.

Conclusion: If naturalism is true then our cognitive faculties are unreliable, then we can't know whether naturalism is true or false. Plantinga states this is

an argument for the irrationality of N, not for its falsehood

Example 1:

A person holds the true belief that there is water to the south. That belief drives the person south to where the water is.

Another person in the same location, however, believes that there are monsters to the north, west, and east, and is driven south towards the water by his false belief.

Yet another person believes that to the south there is an attractive mate and a beanstalk that reaches to the heavens. He's driven south towards the water by his false beliefs.

There is no reason that natural selection should favor true beliefs over false ones when the false ones lead to greater survival.

Example 2:

Person A is thirsty and believes there is water to the south (true). Person A believes thirst is a sign that his body is dehydrated and needs water (true). Once he drinks, he feels energized and believes the water quenched his thirst (true).

Person B is thirsty and believes thirst is a sign from a distant alien that the alien wants to communicate (false). Person B also believes that water is the means by which he can talk back to the alien (false). When person B gets to the water and drinks, he hears kind and encouraging voices in his head that he believes are the alien (false). After drinking, he feels energized and believes the alien gave him power (false).

I know that's a ridiculous example, but it makes the point. Why should natural selection favor Person A's true beliefs over person B's false beliefs?

I suppose you could say that if Persons A and B were to build worldviews based around their experience, Person A's worldview would more closely match up with reality. But their worldviews wouldn't necessarily be mutually exclusive. Perhaps Person C could believe that thirst is a sign of possible dehydration (true) and that it's a sign from an alien (false).

Natural selection may favor the true belief inasmuch as it affects survival, but it does not always select against the false belief.

  • Is it correct to identify their false beliefs as the cause of their survival (points 3 and 4). Surely luck and chance are the true cause of their survival since it is down to luck and chance that their false beliefs just happen to coincide with survival-promoting behaviour. – Nick Jan 9 '16 at 19:54
  • how is this different from saying the probability that Achilles will win a race against a tortus is 1/2 since there are two participants in the race? Sure, it's 1/2 if you throw out all the relevant information about the question. The fact that our species is a product of Darwinian evolution isn't necessarily relevant to the question of whether a particular belief is true. Please tell me I'm missing something. – Tim kinsella Jan 10 '16 at 21:11
  • @Timkinsella Are you saying his argument is trivial? – user18800 Jan 10 '16 at 21:16
  • What do you mean by trivial? – Tim kinsella Jan 10 '16 at 21:18
  • Sorry for the snark, btw – Tim kinsella Jan 10 '16 at 21:25

There are two formulations of the Evolutionary Argument Against Naturalism (EAAN). The one outlined in the cited notes (NOTES) uses the earlier, pre-2008, version where naturalism is described through the relationship between belief and behavior. The more recent formulation in Where the Conflict Really Lies (WTCFL) describes naturalism with materialism "with respect to human beings" (WTCRL, 318). Here belief or the content of cognitive processes either supervenes on or can be reduced to neurophysiological properties. See DicePower's question for further discussion of this distinction.

One problem with the EAAN is that it isn’t clear if rejecting naturalism implies that one should accept some type of theism. Clearly, “Jewish, Moslem, or Christian” theists have an explanation for why our cognitive faculties actually are reliable: “God is the premier knower and has created us human beings in his image, an important part of which involves his giving them what is needed to have knowledge, just as he does” (NOTES, 7). Is “traditional theism” the only way out?

The evolutionary theory Plantinga describes is phyletic gradualism: “natural selection, genetic drift, and other blind processes working on such sources of genetic variation as random genetic mutation” (NOTES, 2). Might an atheist supporting the punctuated equilibria evolutionary theory where species have ontological status avoid the falsification he builds for naturalism?

Does a form of panpsychism offer an atheist an out? Consider Thomas Nagel’s 2012 book, Mind and Cosmos. The subtitle of this book says it all: “Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False”. Nagel is a proponent of panpsychism. See his “What is it like to be a bat?” and “Panpsychism” in Mortal Questions.

Plantinga also writes (WTCRL, 316) that the problem of reliable cognitive faculties under naturalistic evolution has appeared troubling to atheists as well:

Nietzsche, Nagel, Stroud, Churchland, and Darwin, nontheists all, seem to concur: (naturalistic) evolution gives one a reason to doubt that human cognitive faculties produce for the most part true beliefs.

So, one problem with the EAAN is Plantinga doesn’t make it clear how to avoid naturalism without accepting traditional theism. Perhaps that is up to those taking non-theistic or even non-traditional theistic positions to articulate.


I have seen the version of Plantinga's argument that includes your premises 1–3 above, doesn't adopt premise 4, and concludes that since beliefs held by organisms produced by organic evolution aren't necessarily true, naturalism isn't necessarily true. (Note that I don't think any epistemologist would say that beliefs are “generated by natural selection,” as you put it.)

A response to that argument, offered by Michael Ruse among others (e.g. in Ruse's Darwinism and Its Discontents) is that of course it's true that evolved beings are imperfect at truth-acquisition. We are epistemically limited, as philosophers say, and roughly-speaking all philosophers and biologists accept that. However, to the extent that that observation justifies doubt about any one belief like naturalism, it to that same extent can justify doubt about other human beliefs, including alternatives to naturalism. If the observation casts doubt on naturalism, it by the same token casts doubt on supernaturalism and the existence of God. In other words, premises 1–3 are clearly true, and the conclusion that we can't be certain about our beliefs follows from them, but that is unsurprising. And that argument does not help support any less-obviously-true claims Plantinga would like it to help support. Indeed, it undermines them to the same extent.

But you've asked about a version which includes the stronger Premise 4, that “There are more false beliefs that lead to survival-promoting behavior than there are true beliefs that do the same.” It's hard to imagine how Premise 4 could be true, and your example certainly does not support it. The person who goes south and finds water because of the false belief that there are monsters in other directions could just have easily have gone east because of the false belief that there are monsters in the south. Indeed, other things being equal on this simple model, that way of using beliefs to guide action would fail to lead someone to water 75% of the time! Biologically, organisms confused about their environments don't last very long.

So far, that is just to argue, quickly, that Premise 4 is dubious. But we might also want an argument for the view that natural selection generally has, when it has produced belief-forming apparatuses, favored their reliability. That is just to say that organisms with more reliable belief-forming apparatuses have survived at a higher rate than similar organisms with less reliable belief-forming apparatuses. Philosopher Christopher Stephens offers such an argument in the paper “When is it selectively advantageous to have true beliefs?”. He concludes:

The model developed here indicates that natural selection will not always favor true beliefs. However, non-reliable belief formation policies will get the organism into trouble in two basic kinds of cases: ones in which the relevant propositions are systematically important, and cases in which there are several possible actions that the organism must consider, each of which has important consequences. Although not all problems are like this, many (perhaps most), are.

His argument is developed more fully at that link.

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    The revised version of your question (substituting "no more than 50%" for "most") represents more closely the argument rebutted by Ruse, as above. I would add, about your addition, that natural selection doesn't operate on beliefs, as they aren't heritable variation. Yet as Stephens argues, natural selection favors the reliability of knowledge acquisition mechanisms under some circumstances, contra your revised P4. And we're back to the point that of course having some false beliefs is consistent with survival, but that that doesn't help Anti-naturalism. – ChristopherE Jan 9 '16 at 21:34
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    Sorry, that's not the case; natural selection works on heritable variation. Unless you believe that beliefs are genetically determined (and even if any were, certainly the beliefs in question for Plantinga are not), beliefs are not heritable variation. – ChristopherE Jan 9 '16 at 22:23
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    No, @IsThatTrue, it's not the case that"P(B(SNT)/SN) is left intact" by the EAAN, if by "intact" you mean "on a better epistemic footing." The EAAN only reaches its conclusion by invoking skepticism which the supernaturalist has to answer to, too. So, if it points out that the naturalist has a tough time defeating that skepticism, that's true, but the same skepticism equally damages beliefs under supernaturalism. Plantinga argues the first part (so yes, I understand that's his point), but doesn't acknowledge the second. Supernaturalism per se isn't in better shape to answer skepticism. – ChristopherE Jun 4 '16 at 13:39
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    No, I know all that, and that Plantinga would like to leave the argument there. But notice that your interpretation makes the EAAN trivial. EAAN is only epistemically significant if it shows that under Naturalism one is on worse epistemic footing than if one doesn't assume Naturalism. And the EAAN, by implicitly restricting its ambitions in the way you describe, fails to make that case. Beyond that limited scope of the EAAN, the idea that “ A supernaturalist … does not have to answer skepticism," while a naturalist does is uh ... optimistic. – ChristopherE Jun 7 '16 at 18:28
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    @IsThatTrue I think you may be under the misconception that evolutionary biology is an argument. – ChristopherE Apr 24 '18 at 20:21

Plantinga is playing a semantic trick in his last step by switching R (reliability) with N (naturalism) which destroys his reliance on Bayes' theorem. He concludes that our belief forming mechanisms are unreliable and therefore our belief in naturalism is unreliable, so it is unlikely to be true under naturalism, if we assume naturalism. This is false. If we assume naturalism, naturalism is, by definition, true.

Put mathematically, P(N|N) = 1 by definitions*

Even if something is improbable under some arguments, if it is true, it is true.

If Plantinga was employing no trickery he could not arrive at any conclusion other than this.

Plantinga's semantic trick covers up that his argument is actually an excellent one for showing great evidence for evolution and naturalism. As Platinga correctly points out, we'd expect both people with false beliefs and true beliefs under naturalism and evolution, since false beliefs could still lead to survival. And this is exactly what we see: people with both true beliefs and false beliefs (e.g. people who believe in a flat earth).

If, instead, our formation of beliefs was rooted in a perfect being who guaranteed our beliefs were true, we'd expect everyone to agree on what is true, and that is exactly what we do not see.

It seems to me that Plantinga has come extremely close to the correct conclusion, but he's unfortunately fallen at the last hurdle.

There have been philosophers who have also made the observation that Plantinga has a less than firm grasp of the mathematics, Elliot Sober:

Not only is a low value for Pr( X | Y ) not sufficient for Y ’s defeating X; it also is not necessary, if defeaterhood is to ground the idea of self-defeat.The reason is that Pr( Y | Y ) = 1, for all Y .And as difficult as it is to connect low probability to defeaterhood, it seems even harder to see why the inscrutability of Pr( X | Y ) should help establish that Y defeats X

In his last section, Sober also makes similar observations concerning that Plantinga's argument, rather than being a serious problem for evolution, which expects bad belief forming mechanisms, it is rather a very serious problem for theists, who, Plantinga argues, should expect good ones.

*Here, for instance, one can read about probability mathematics. From the definitions given there, we can do a bit of math (Using arbitrary arguments A and B)

P(A|B) = P(A ∩ B)/P(B)

If we let A = B, we get

P(A|A) = P(A ∩ A)/P(A)

we also have that

P(A ∩ A) = P(A) + P(A) - P(A ∪ A)

P(A ∪ A) is the probability that A occurs OR A occurs, it can be seen from the diagram on page 2 from the link above that it would be true that P(A ∪ A) = P(A) (this is formally provable using set theory, which gives you A ∪ A = A ((and also A ∩ A = A)) but it is perhaps more illustrative to those not versed in mathematics when shown this way)

so we have P(A ∩ A) = P(A) + P(A) - P(A)

therefore P(A ∩ A) = P(A)

and therefore P(A|A) = P(A)/P(A) = 1

  • Would you have references to people who share your view? This would give the reader a place to go for more information and strengthen your answer. Welcome to this SE! – Frank Hubeny Nov 16 '18 at 3:25
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    I've included a link on probability mathematics and expanded on why P(N|N) = 1. I don't know of any philosophers who support my views, they come just from seeing the fallacy in the mathematics being presented. – magnus.orion Nov 16 '18 at 4:29
  • I've updated with reference to Elliot Sober, who presents a variety of arguments, including Plantinga's failure to grasp mathematics – magnus.orion Dec 5 '18 at 4:49
  • The post is kind of difficult to follow because it starts with formulas, which moreover have undefined letters in them. It might help if you started by stating what you are trying to show ("Plantinga is playing a semantic trick..."), then explained it informally, and moved the formulas to the end of the post into a kind of appendix. It would also help readability if you used the standard operation symbols, like ∩ and ∪. – Conifold Dec 5 '18 at 7:48
  • Thanks for the advice. Perhaps this is a better attempt? – magnus.orion Dec 5 '18 at 16:50

The EAAN is not even wrong.

The first problem is that beliefs are not inherited traits. Natural selection may well favour individuals whose beliefs lead them to greater reproductive success, and these beliefs may well be passed down culturally to their offspring, but the theory of evolution has nothing to do with this. Prof Plantinga clearly has no idea about the theory of evolution.

The second obvious problem is that the EEAN is that it is based on a dualistic notion that beliefs have a neurophysiological structure and associated semantic content. The example of a hominoid running away from a tiger whilst thinking he is trying to pet it shows how Prof Plantinga thinks about how the mind works. However, the modern way in which the brain is thought to work is that part of the brain controls our flight from a danger, such as tiger, with no semantic content whatsoever whilst a separate part of the brain is responsible for language and the semantic content of thinking. Creatures with no areas of the brain capable of language still have a part of the brain capable of recognizing and fleeing from danger, but will have no beliefs about this. Humans have inherited these brain structures, but have an additional part of the brain capable of forming semantic content and beliefs, but which are not inheritable. Prof Plantinga clearly has no idea of theories of how the brain works.

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