Saturday, March 17, 2018

Post-EAAN Debate Reflections (p. 2)

Post-EAAN Debate Reflections
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The Defeater Thesis



To defend the Defeater Thesis I’ll use a number of scenarios that involve the fictional drug XX used in a scholarly paper titled A Mental States Approach to the Evolutionary Argument Against Naturalism. Drug XX renders one’s cognitive faculties unreliable within two hours for the vast majority of those who take it. The minority have a blocking gene that codes for a protein that blocks the effect of the drug. The XX-mutation a genetic mutation that injects drug XX into the bloodstream soon after one is born. The gist is basically that N&E is like ingesting drug XX when it comes to providing a defeater for R. I claim that R is defeated in each of the followings scenarios:

Scenario (1): I know that my friend Sam ingested drug XX and that twenty-four hours later he came to believe that that a series of tests has confirmed that he has the blocking gene and that his cognitive faculties are reliable, though I have no independent reason for thinking this occurred. And since Sam obtained his belief about the cognitive tests long after he ingested drug XX, there’s a reasonable chance that this belief was produced by unreliable cognitive faculties, and so this would-be evidence for Sam’s cognitive reliability (Sam’s memory of passing the cognitive tests) is undermined by drug XX, and my belief Drug XX entered Sam’s bloodstream defeats my belief that Sam’s cognitive faculties are reliable.

Scenario (2): I ingest drug XX and know of no relevant difference that distinguishes my case from Sam’s. Days later I come to believe I have taken a series of tests that say I have the blocking gene and that my cognitive faculties are reliable, but since this belief came long after I ingested drug XX, it seems this would-be evidence for my cognitive reliability (my memory of passing the cognitive tests) is undermined by drug XX, just as the would-be evidence for Sam’s cognitive reliability (Sam’s memory of passing the cognitive tests) is undermined by drug XX in (1). Thus my belief Drug XX entered my bloodstream defeats my belief that R is true with respect to me.

Scenario (S3): A doctor has injected me with drug XX soon after I was born, and I come to believe in the following. I am a renowned scientist who has built a machine that I know is capable of reliably detecting whether and when drug XX entered a person's bloodstream, and I am extremely confident about the reliability of this machine. I administer the test to myself and the machine reports that drug XX entered my bloodstream at around the time I was born; as such, I am as confident that drug XX entered my bloodstream as I am in scenario (2). Later I come to believe I have taken an extensive battery of cognitive reliability tests to confirm that I have the blocking gene, but since this belief came long after drug XX entered my bloodstream, it seems this would-be evidence for my cognitive reliability (my memory of passing the cognitive tests) is undermined by drug XX just as it is in scenario (2), and so it seems my belief Drug XX entered my bloodstream soon after I was born defeats my belief that R is true with respect to me.

Scenario (4): I come to believe in the following. The XX-mutation afflicts approximately one in a million individuals, with only a small percentage of those with the XX-mutation having the blocking gene. I have constructed a device similar to the one described in (3) except this device detects whether evolution gave someone the XX-mutation, and I am as confident in the reliability of this machine as I am with the one in (3). The machine reports that I have the XX-mutation and thus that drug XX entered my bloodstream soon after I was born. Later I come to believe that I’ve passed a series of cognitive tests to confirm that I have the blocking gene, but since I believe these tests happened long after drug XX entered my bloodstream, it seems that this would-be evidence for my cognitive reliability is undermined by drug XX just as it is in scenario (3). My belief Drug XX entered my bloodstream soon after I was born defeats R for me here just as it does in scenario (3). Similarly, my belief that I have the XX-mutation (since I believe this mutation injects drug XX into my bloodstream soon after I’m born) defeats my belief that R is true with respect to me.

Scenario (5): I come to believe in the following. Via a nifty combination of scientific and philosophical argumentation, it is proven beyond all reasonable doubt that naturalistic evolution entails that the XX-mutation is inevitably a part of any humanoid’s genetics. The aforementioned scientific and philosophical argumentation say that given N&E, it is likely that the XX-mutation rendered everyone’s cognitive faculties unreliable, though on N&E there is also the small chance that everyone evolved the blocking gene to render everyone immune to drug XX. N&E entailing that the XX-mutation is part of our genetics thus makes Pr(R|N&E) low, and I thus come to believe Pr(R|N&E) is low. I believe some time after it’s discovered that drug XX entered our bloodstream, credible scientists have run cognitive tests to confirm that we have the blocking gene. But since this belief came long after drug XX entered my bloodstream, it seems that, like scenario (4), this would-be evidence for my cognitive reliability is undermined by drug XX. My belief I have the XX-mutation defeats R for me here just as it does in scenario (4).

Scenario (6): The Probability Thesis is true and Pr(R|N&E) is low, but I do not initially believe this and instead think I am the product of a sort of evolution that makes my cognitive reliability very likely. Later however I study philosophy and see for myself that the probability of my humanoid cognitive faculties being reliable given that I am a product of naturalistic evolution is low. Afterwards I come to believe I have taken an extensive battery of tests that establish my cognitive reliability, but since this belief came long after naturalistic evolution created my cognitive faculties and I believe that given N&E, naturalistic evolution has a high probability of giving me unreliable cognitive faculties, it seems that this would-be evidence for my cognitive reliability is undermined by the effects of naturalistic evolution similar to how naturalistic evolution giving me the XX-mutation in scenario (5) undermines my would-be evidence for R, and so it seems that I have a defeater for my belief that my cognitive faculties are reliable.

Scenario (6) is of course just the scenario of the Defeater Thesis: Pr(R|N&E) is low defeating R (for the naturalist who accepts evolution). Summarizing the scenarios and their defeaters for R:
  1. Sam ingested drug XX defeats R for Sam.
  2. I ingested drug XX defeats R for me.
  3. Drug XX entered my bloodstream as an infant defeats R.
  4. I have the XX-mutation (but most don’t) defeats R.
  5. I have the XX-mutation (everyone has the mutation) defeats R.
  6. Pr(R|N&E) is low defeats R.
The reasoning for the Defeater Thesis is this:
  1. R is defeated in scenario (1).
  2. If R is defeated in scenario (1), R is defeated in scenario (2).
  3. If R is defeated in scenario (2), R is defeated in scenario (3).
  4. If R is defeated in scenario (3), R is defeated in scenario (4).
  5. If R is defeated in scenario (4), R is defeated in scenario (5).
  6. If R is defeated in scenario (5), R is defeated in scenario (6).
  7. Therefore, the Defeater Thesis is true.
The general idea is that there doesn’t seem to be any relevant difference between the two scenarios of any premise (2) through (5) above where R is defeated in one scenario but not defeated in the other. If that’s true, and R is defeated in scenario (1), then the Defeater Thesis is true.

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