|Evolutionary Argument Against Naturalism|
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Overview of the Evolutionary Argument Against Naturalism
To define some terms and abbreviations, a defeater is (roughly) something that removes or weakens rational grounds for accepting some belief; in the context of the EAAN, the defeater is such that one is rationally obligated to withhold the defeated belief (i.e. not believe it; as by (1) remaining agnostic about it, or (2) believing it to be false). Suppose for example I arrive in a city and see what appears to be a barn from fifty meters away. I later learn that some eccentric has last week put up fake barns all over the area along with real ones, and that these fake barns are indistinguishable from real barns when viewed at a distance of thirty meters or more. I now have a defeater for my belief that I had seen a barn. I realize I could have seen a barn, but I don’t have sufficient grounds to accept the belief anymore. The rational thing for me to do is to withhold my belief that I had seen a barn. Suppose though I learn later that the eccentric removed all fake barns prior to my arrival. I would then have something that nullifies the defeating force of the defeater, i.e. a defeater-defeater.
Somewhat more precisely for the analytically inclined, in the context of the EAAN a defeater is a belief D that defeats another belief B for someone if that person would no longer have adequate grounds to believe B when coming to believe (and continuing to believe) D. So in our barn example (prior to learning that the eccentric removed the fake barns), the defeater D is “An eccentric put up fake barns in the area that are indistinguishable from real barns at the distance I was looking,” which defeats belief B “I saw a barn.” As long as I believe D, I cannot reasonably believe B with the information that I have. EAAN claims the naturalist who believes in evolution acquires a defeater for his belief in evolution + naturalism. The abbreviations commonly used for EAAN:
|R =||One’s cognitive faculties are reliable|
|N =||naturalism is true|
|E =||evolution is true|
|Pr(R|N&E) =||the probability of R given N&E|
In other words, Pr(R|N&E) refers to the probability that our cognitive faculties are reliable given naturalism and evolution, where by “cognitive faculties” the EAAN is referring to those faculties that process or produce beliefs—such as memory, perception, and reasoning. In a nutshell, the evolutionary argument against naturalism goes like this:
- Pr(R|N&E) is low
- The person who believes N&E (naturalism and evolution) and sees that Pr(R|N&E) is low has a defeater for R.
- Anyone who has a defeater for R has a defeater for pretty much any other belief she has, including (if she believed it) N&E.
- If one who accepts N&E gets a defeater for N&E in the manner described in lines (1) through (3), N&E is self-defeating and can’t be rationally accepted.
- Conclusion: N&E can’t be rationally accepted (at least, not for the N&E believer who accepts premise (1)).
Of course defeaters can be themselves be defeated; so couldn’t you get a defeater for this defeater—a defeater-defeater? Maybe by doing some science—for example, determining by scientific means that her cognitive faculties are reliable? Couldn’t she go to the MIT cognitive-reliability laboratory for a check-up? Clearly that won’t help. Obviously that course would presuppose that her cognitive faculties are reliable; she’d be relying on the accuracy of her faculties in believing there is such a thing as MIT, that she has in fact consulted scientists, that they have given her a clean bill of cognitive health, and so on.Any would-be evidence or argument for one’s cognitive reliability would be relying on the very cognitive faculties that are being called into question, so the defeater mentioned in premise (2) would be an undefeated defeater.
Note also from Plantinga’s quote that we get a feel for what type of cognitive unreliability EAAN has in mind; this isn’t ordinary fallibility, the kind that we could compensate for by scientific methods and peer review, but a kind of general cognitive unreliability such that one can’t even trust one’s memory of whether one passed cognitive reliability tests.
So much then for an overview of the argument. Both the Probability Thesis and the Defeater Thesis of EAAN will need to be justified. Up next, justifying the Probability Thesis.
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 Plantinga, Alvin. Where the Conflict Really Lies (New York, New York: Oxford University Press, 2011), p. 344-345. Though I worded it slightly and I added the “pretty much” part to avoid possible controversies that things like cogito ergo sum and I am being appeared to redly might create, since by my lights the fact that there might be a few exceptions like this don’t affect the heart of the argument.
 Plantinga, Alvin. Where the Conflict Really Lies (New York, New York: Oxford University Press, 2011), p. 354