|Post-EAAN Debate Reflections|
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To define some terms and abbreviations, a defeater is (roughly) a belief that undercuts the justification for another belief. To illustrate, suppose I see what seems to be a barn from twenty meters away and I form the belief That’s a fine barn but later I believe a local when she tells me that a bunch of barn facades were in the area along with real ones. My belief There were barn facades in the area defeats my belief that I’d seen a barn. Naturalism is the view that the supernatural does not exist. Some abbreviations:
|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)). 
Beliefs have semantic content (e.g. the belief that Snow is white and the belief that Two plus two equal four) and are associated with neurophysiological (NP) properties. If naturalism is true, the semantic content of a belief is causally irrelevant in the sense that it doesn’t matter which semantic content is associated with the NP properties; the same outcome in the physical world (e.g. one’s behavior) would result. A deductive argument:
- (On naturalism) If a belief’s associated NP properties had any different semantic content associated with it instead, the same outcome in the physical world (e.g. one’s behavior) would result.
- If (1) is true, then a belief’s semantic content is causally irrelevant (on naturalism).
- Therefore (On naturalism), a belief’s semantic content is causally irrelevant.
Justification for (2): True by definition; by “semantic content being causally irrelevant” I just mean it doesn’t matter which semantic content is associated with the NP properties; we’d get the same physical outcome.
So why would it matter if N&E entails that the semantic content of our beliefs is causally irrelevant? To avoid bias against our own species, think not of us but of alien creatures whose physiology is radically unlike our own, and let RA represent “The cognitive faculties of the aliens are reliable.” N&E is true for these aliens, thus making the semantic content of their beliefs causally irrelevant. Then on N&E the electrochemical reactions that cause the behavior of these aliens could generate any semantic content at all (e.g. 2 + 2 = 1 or Grass is air) without that content affecting behavior. The semantic content could even be “garbage” beliefs unrelated to the external environment, as in dreams, and it still wouldn’t affect behavior.
To illustrate the potential problem this creates, suppose a random belief is assigned for the answer to “What does two plus two equal?” Answers of one, two, rock, and sunshine would all be wrong. Randomly selected beliefs about the color of the sky and one’s age are similarly likely to be wrong. The enormous variety of garbage belief sets akin to dreams vastly outnumber those belief sets that accurately resemble one’s external reality. Since semantic content would be a causally irrelevant and useless byproduct of the biological processes, while it is still possible for the electrochemical reactions that produce advantageous behavior to also produce a reliably true belief set (as opposed to a garbage, dream-like one), it would be a very serendipitous coincidence indeed if the NP properties of our aliens also generate reliably true beliefs given just N&E. We thus have the following deductive argument, with RA representing “the cognitive faculties of the aliens are reliable.”
- If Pr(RA|N&E) is low, then Pr(R|N&E) is low.
- Pr(RA|N&E) is low.
- Therefore, Pr(R|N&E) is low.
Justification for (2): Here’s what we know about our alien species on N&E:
- Semantic content is a causally irrelevant and useless byproduct of the evolutionary process.
- Garbage belief sets vastly outnumber ones that accurately resemble one’s external reality.
- We have no a priori reason to believe an alien would have an accurate belief set instead of one of the far more numerous garbage belief sets.
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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.