At Jim's request, here is the aesthetic argument against naturalism. I admit that I am not a trained analytic philosopher, so forgive the impreciseness of my argumentation. At the same time, I believe that the idea I'm trying to get across in my argumentation is more fundamental than the argumentation itself. So, even if my syllogisms don't amount to a formal mathematical proof, hopefully the reader will look past that and try to get the underlying idea.
Sounds reasonable. I'll try to avoid too much deconstructive hoo-ha.
First some quick pseudo-definitions:
Naturalism: everything is fundamentally the product of some material cause.
Aesthetics: that which deals with the subject of beauty.
Immediately we're running into problems. Naturalism is often conflated with materialism, but the two aren't synonyms. Can the argument be salvaged by thinking "physicalism" or "materialism" whenever Eric writes "naturalism?" We'll see.
Now the argument:
During my life, I've had moving experiences of what I would call beauty. These experiences are powerful and have a strong physical and mental effect on me. These experiences also include the belief that they are real, as real as when I think I see something red or that I am talking to another person. Naturalism claims that such a thing as 'beauty' does not exist. Instead, my experience would be brought about by different material causes, such as chemicals in my brain, something I ate, etc. Consequently, whenever the 'beauty faculty' tells me something is beautiful I must say "No, according to the naturalist it is not," and thus not allow myself to have the experience of beauty.
This straw version of physicalism is worthily and easily knocked down. But it's straw. Consider:
When I see X, pleasure neurons A and B fire.Is it subjective? Yes. Is it a gross caricature? Probably. I'm less of a philosopher than Eric. But I don't see any contradiction, internal or external, that places this scenario outside the bounds of physicalism, even in its crudest forms.
I have come to associate X with similar items that also fire up A and B.
I call this particular brain-state "beauty."
Therefore, X, like any other object that brings about this brain state, is "beautiful."
To the charge that physicalism undermines aesthetics, commenter Phil adds, "According to naturalism, an idea isn't really an idea, it's just neurons firing in your brain." Where does that "just" come from? It's a value judgment tacked onto a scientific explanation. But if naturalism is true and somehow undermines value judgments, then that "just" has no place in the discussion, making the objection internally contradictory and self-defeating. (How's that for a reductio?)
To begin with, this just seems kind of arbitrary. Why only accept some perceptions of 'reality' based off of a theory that has not been proven? That just seems to beg the question, especially since beauty sometimes seems more real to me than the observations upon which science is built. Why not also accept the observations of beauty? They don't undermine science, just naturalism, and naturalism is not necessary for scientific advance. Plus, if you listen to some of the great scientists, i.e. Einstein, it seems that beauty in fact inspires scientific progress.
Given the above, these objections are irrelevant. Let's move on.
Next, it seems hard to account for such a belief in beauty via naturalism, especially since a naturalistic explanation undermines the belief. Unfortunately, this is more of an intuitive notion for me right now as to why exactly that is. The thought process is that as I focus on my perception of beauty and then try to explain it by some third person perspective I just don't seem to really be explaining the perception, but just accidental features of it.
If I understand the complaint rightly, this is definitely a problem for physicalism. But no one has a satisfactory explanation for how qualia come about, so all mental models walk the same runway.
Finally, in the practical world naturalism undermines itself. Naturalism undermines all that has in the past motivated man to be willing to die in the defense of others. Thus, the more naturalistic man becomes the weaker he is, which also applies to nations.
How has materialism undermined human motivation for self-defense, or the defense of others? I'd love to see the evidence.
As a general aside, the argument against physicalism seems to presume that knowledge deflates enjoyment--call it the "Wizard of Oz objection." As a counterexample, I find helium-heightened voices hilarious. Yet never have I found them less funny because I know that it's "just" helium letting vocal cords vibrate faster, and not a magical transformation.