Sunday, March 18, 2018

Mental States are Causally Irrelevant on Naturalism

Home > Philosophy > Metaphysics
  1. Problems for Naturalism
  2. Why Mental States are Causally Irrelevant on Naturalism
  3. The Symbolic Logic
  4. Proving It
  5. The Argument is Sound, but So What?

Problems for Naturalism



Naturalists typically believe that brain states determine mental states. Roughly, the gist of what I mean by mental states being causally irrelevant on naturalism is that on naturalism it doesn’t which mental state is associated with a brain state; the brain’s causal behavior would be the same even if no mental state were associated with it. The upshot is that if naturalism is true, mental states getting associated with our brain states is a causally irrelevant and useless byproduct of our biological processes. This raises problems for naturalism.

We normally think that our mental states (elements of mental states include sense experiences, memories, thoughts, etc.) have something to do with our behavior; e.g. a mental state yielding the belief that I am thirsty and this water will quench my thirst will yield different behavior, ceteris paribus, then if my mental state instead yielded the belief that This water will kill me and I don’t want to die.[1] If our mental states are causally relevant to behavior, and on naturalism mental states are not causally relevant to our behavior, then naturalism is false.

Another problem is that mental states being causally irrelevant on naturalism implies that the likelihood of a humanoid’s cognitive faculties being reliable given naturalism and evolution are low. I went into this in my debate on the evolutionary argument against naturalism (EAAN) but I can illustrate the problem with this thought experiment about aliens that are humanoid (not only in having a human shape but also human-level intelligence in terms of complexity of thought, can form beliefs, change beliefs, etc.) whereby naturalism and evolution are true for them and we have no further relevant information.

What can we know from naturalism and evolution being true for these aliens? Natural selection selects for advantageous behavior, but not necessarily for true beliefs. Since on naturalism the mental states of the alien humanoids are causally irrelevant, then when the alien brains that produce advantageous behavior also produce a mental state, none of the many conceivable mental state associations with the alien brains—even “garbage” mental states unrelated to their external environment (as in dreams)—would affect behavior. Garbage mental states vastly outnumber accurate mental states (i.e. those that accurately reflect one’s external reality), so while it is possible that the alien mental states are accurate, given just the information we have from evolution and naturalism (garbage mental states vastly outnumber accurate mental states, mental states are a causally irrelevant and useless byproduct the biological process, etc.) it would be a very serendipitous coincidence that the alien brain states that generate advantageous behavior also happen to generate accurate mental states, and it seems more likely that our aliens are effectively living in a dream world. Thus, the likelihood that the alien cognitive faculties are reliable given just the information we have (naturalism and evolution) is low.

We can use the results of this alien thought experiment in an argument for the reliability of our cognitive faculties being unlikely on naturalism and evolution. Before delving into the argument, here’s the basic symbolization key:

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


The argument that Pr(R|N&E) is low with RA representing “the cognitive faculties of the aliens are reliable” is this:
  1. If Pr(RA|N&E) is low, then Pr(R|N&E) is low.
  2. Pr(RA|N&E) is low.
  3. Therefore, Pr(R|N&E) is low.
Justification for (1): What’s true for the humanoid aliens here is also true for us, since we are basically considering the probability of R on just N&E (we considered Pr(RA|N&E) merely so we could try thinking about the issue in a way that avoids bias towards our own species).

Justification for (2): Here’s what we know about our alien species on N&E:
  1. Mental states are a causally irrelevant and useless byproduct of the biological process.
  2. Garbage mental states vastly outnumber ones that accurately resemble one’s external reality.
  3. We have no a priori reason to believe an alien would have an accurate mental state (one that accurately reflects their external reality) instead of one of the far more numerous garbage mental states.
We’re basically trying to evaluate the likelihood of RA given just N&E, so points (a), (b), and (c) together suggest that given just the information we have here, it is considerably more likely that the aliens have unreliable cognitive faculties (garbage mental states being far more numerous) than reliable ones.

In the EAAN, the claim that Pr(R|N&E) is low is called the Probability Thesis, and the claim that the naturalist who sees that Pr(R|N&E) is low undercuts the naturalist’s justification for believing R is called the Defeater Thesis. Mental states being causally irrelevant on naturalism suggest that the Probability Thesis is true. I explained why I think the Defeater Thesis is true in the debate on the evolutionary argument against naturalism (you can also see page 2 of the EAAN debate recap if you want it summarized).

Thus if on naturalism mental states are causally irrelevant, this poses major problems for the naturalist. First, it seems to be true that our mental states are causally relevant. Second, mental states being causally irrelevant suggest that Pr(R|N&E) is low, which is a major component of using evolution to argue against the rationality of naturalism (if naturalism intellectually undercuts itself via evolution, that’s very bad for naturalism!). But why think that on naturalism, our mental states are causally irrelevant?

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[1] I’m using “yield” to get around technical difficulties of semantic externalism I explained in my previous post-debate EAAN article. Basically, the issue is that people can have identical mental states but the semantic content of their beliefs can be different due to different referents. For example, consider two planets with identical inhabitants possessing identical mental states, and each say, “The sun is bright” when pointing at their sun, but the phrase “The sun” refers to different objects on those two planets. Nonetheless, a person’s mental state obviously plays a role in what beliefs they have and whether those beliefs are reliably true; e.g. the sort of mental states one has in chaotic dreams do not align with one’s external reality particularly well.

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