The Evolutionary Argument Against Naturalism (Pt. 2)

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Last time, I introduced Alvin Plantinga's argument that believing in both evolution and naturalism results in a general belief-reliability crisis. Since I do hold both of these beliefs, I'm motivated to reflect on his argument and figure out whether I need to make an adjustment.

Bold vs. Cautious

I would characterize Plantinga's argument as bold because he reaches for the conclusion that actual, human believers in both evolution and naturalism have a general defeater for their beliefs. At least, they do after grasping his argument.

He is suggesting that I, Garren, have better reason to believe my beliefs are mostly false than to believe my beliefs are mostly true. I can't take this seriously. It's like telling Philosophy freshmen about Descartes' demon that systematically deceives one's senses, and expecting the students to really doubt everything.

But to have a defeater for [the belief that my cognitive faculties are reliable] it isn't necessary that I believe that in fact I have been created by a Cartesian demon or been captured by those Alpha-Centaurian superscientists. It suffices for me to have such a defeater if I have considered those scenarios, and the probability that one of those scenarios is true, is inscrutable for me. It suffices if I have considered those scenarios, and for all I know or believe one of them is true. In these cases too I have a reason for doubting, a reason for withholding my natural belief that my cognitive faculties are in fact reliable.¹

Plantinga's alternative is to accept another story that an external Agent wanted me to mostly believe true things, so He tinkered with evolution to give me reliable belief-forming mechanisms...except when it comes to the stunningly important belief that He exists.

At this point, I must admit that naturalistic evolution does have a major disadvantage: there is less room to simply make up convenient stories about it.

I propose a toned down, cautious version of the argument which doesn't deal with skeptical scenarios. There's no need to claim actual, human believers in evolution and naturalism are involved in a belief-destroying vortex. Instead, Plantinga could argue that theistic evolution provides a better explanation than naturalistic evolution when it comes to the unquestioned premise that we do have (more or less) reliable belief-forming mechanisms, i.e:

If true, theistic evolution would neatly explain why we have reliable belief-forming mechanisms.

If true, naturalistic evolution would provide a very poor explanation of why we have reliable belief-forming mechanisms.

By inference to the better explanation, theism beats out naturalism.

Can Naturalistic Evolution Offer A Decent Explanation?

Suppose evolution is true and naturalism provably can't ever provide a decent explanation for our (more or less) reliable beliefs. Naturalists might still resist the notion of divine intervention because of other considerations that count against theism or for naturalism, but I grant that the consideration we're considering would be a strong point against naturalism.

Now, the important question is whether Plantinga is offering a reason to think naturalism can't ever provide an explanation, or is he merely pointing out the current lack of such an explanation? It would be easy to dismiss him, if his argument were another "How could evolution design an eye?" or some similar structural mystery. These questions keep turning up reasonable answers.² But it's clear that the kind of "beliefs" he is concerned about are not just a matter of physical structure.

To paraphrase:

Naturalists these days all seem to be materialists. What sorts of things are beliefs under materialism? Neural events or states hooked into the overall operation of the brain. "So considered, beliefs will of course be able to enter the causal process that leads to behavior."³

But, any properly-so-called belief must also have the property of being associated with a proposition, e.g: that Frank Herbert wrote Dune. Otherwise, the neurophysiological event wouldn't really be about anything. "How does a neural event somehow get assigned a certain proposition as its content? It is hard to think of any scenarios that are as much as decently plausible."³ And, once assigned, the propositional content itself would be an irrelevant bystander to the physical operation of the brain.

So you see, the core of Plantinga's argument has to do with the nature of propositions. The naturalistic evolution of neurophysiological states (or events) which are generated in response to sensory input and which inform behavioral output goes completely unchallenged.

This makes the Evolutionary Argument Against Naturalism a fairly niche philosophical concern, perhaps one that is only conceivable for those who take proposition or property talk too seriously. Consider a maze-learning robot that adds information to its internal state, engages in some reasoning to infer when it has probably been dropped into a different point of a past maze, and makes goal-oriented choices based on its internal map. If the robot has reasoned that the goal is probably three feet forward, ninety degrees to the right and six inches forward again, then I would say the robot believes the goal is located there.

We could say the relevant bits of computer memory are "associated" with the propositional content that the goal is three feet forward and six inches to the right. Then we could worry how this separate content-bearing property can reach back into the robot's cybernetic brain and causally influence the bits and volts. Or, just maybe, we could question the philosopher's analysis that took the propositional content out of the realm of causally informed (and informing) bits and volts in the first place.

I admit unfamiliarity with the philosophy of propositions, but it seems plausible that they are just linguistic descriptions of possible world states. A belief may be associated with a world state without involving a linguistic description of that state (though some Postmodernists may disagree). The robot internally represents a possible state of the maze, then we use language to describe that state, and feel the description is both integral and external to the robot's electronic belief. I suspect something like this underlies Plantinga's dualistic intuition.

At any rate, his argument doesn't cause me a lot of concern about the rationality of believing in both evolution and naturalism. I'm much more inclined to think analytic philosophers sometimes generate their own problems, and this is one of those times.


1. Plantinga, A. (2002). Introduction. In Beilby, J. (Ed.), Naturalism defeated? (1-12). Ithica, New York: Cornell University Press. p 11.
2. Dawkins did a fun visual demonstration of eye evolution in Growing Up in the Universe.
3. Plantinga, A. (2002). Reply to Beilby's Cohorts. In Beilby, J. (Ed.), Naturalism defeated? (204-275). Ithica, New York: Cornell University Press. p. 212-213.