Sunday, May 19, 2013

Evolutionary Argument Against Naturalism

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Evolutionary Argument Against Naturalism
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Some atheists claim there is a conflict between science and religion. But what if there were a conflict between naturalism (disbelief in the supernatural) and science? Enter the evolutionary argument against naturalism (EAAN), a remarkable argument that uses the theory of evolution to argue against the rationality of naturalism. This argument was originated by Christian philosopher Alvin Plantinga.

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. EAAN claims the naturalist who believes in evolution acquires a defeater for his belief in evolution + naturalism. The abbreviations commonly used for EAAN:

R = our 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. In a nutshell, the evolutionary argument against naturalism goes like this:
  1. Pr(R|N&E) is low
  2. The person who believes N&E (naturalism and evolution) and sees that Pr(R|N&E) is low has a defeater for R.
  3. 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.
  4. Therefore, the devotee of N&E (at least such a devotee who is aware of the truth of premise 1) has a self-defeating belief.
Call premise (1) the Probability Thesis and premise (2) the Defeater Thesis. Denying the truth of evolution isn’t much of an option for the naturalist, so if the above evolutionary argument against naturalism is sound, the naturalist is in serious trouble. But defeaters can themselves be defeated as in the case of the barn scenario I described, so could a defeater-defeater be present for the naturalist here? Couldn’t the naturalist run through a battery of tests to confirm her cognitive reliability? Not quite, since the naturalist would be relying on her cognitive faculties to even believe there is such a thing as scientists and cognitive tests, in addition to believing that she has passed them, and if she has a defeater for R, she’s pretty much screwed. So the defeater mentioned in premise (2) would be an undefeated defeater.

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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