Some of Holtz's points are a bit quick and it is uncertain to which argument the author is responding.

"Nature is comprehensible scientifically only if nature is not a causally closed system--only if nature is shaped by supernatural forces." If this is the conclusion, nothing about Koons in Holtz's article supports this. Judging by Koon's original article, this is a weakness in Koon's original argument.

Holtz rejects the definition of naturalism as the position that no causes outside space-time influence anything in space-time and favors one that is centered on the causal role of agency. Something like a combination of both definitions is probably better, though I would prefer the more general 'physical' than 'spatiotemporal' criterion, since there may well be physical things that are not spatiotemporal (e.g., quantum foam).

In any case, if Holtz took Koon's definition and ran with it, for the sake of argument, it is difficult to see how the conclusion that "Nature is comprehensible scientifically only if nature is not a causally closed system" follows from anything Koons himself says.

Holtz seems to be making this point: aesthetic considerations do not *cause* theories to be true, they are simply useful tools for finite human beings to wield when trying to evaluate competing theories.

Koons says that scientific realism means:

 a. Our scientific theories and models are theories and models of  the real world
 b. Scientific methods tend, in the long run, to increase our stock of real knowledge

But on these definitions scientific theories need not even correspond exactly to reality--i.e., we are talking scientific likelihood, not metaphysical certainty. *Models* of the real world are just that--models--and scientific method *tends* to increase knowledge long-term. Given such a flexible definition of "scientific realism", it is  hard to see how it could be shown to be incompatible with almost anything.

Another reviewer writes:

Holtz's article should be revised to more explicitly address the 5-step argument that is the core of Koons' argument. Holtz is clearly arguing against step 4, but it is not clear what he would say to try to respond to the apparent confusion he sees in what Koons says in steps 2 and 3.

For the purpose of Koons' argument, my version of naturalism is effectively the same as his: a causally closed world (ON) in which knowledge and intentionality is reducible to non-mental phenomena (RN). My criticism of the details of Koons' definition of naturalism is independent of my criticism of his paper's central argument.  I've updated my paper to make this explicit.

Holtz writes that "Koons' argument rests on a mistaken premise that 'the pervasiveness of the simplicity criterion in our scientific practices' is an empirical conclusion rather than a methodological assumption." It is not clear that Koons makes this mistake. Holtz ultimately argues that simplicity is neither an empirical conclusion nor a methodological assumption, but is part of the definition of truth. When he makes this move, he shifts from talk of a simplicity criterion to talk of parsimony,

I take parsimony to be the simplicity criterion in epistemology, and I consider one's definition of truth to be a methodological assumption in one's epistemology, so I don't understand how either consideration constitutes a shift.

and then further shifts to the point where he speaks of "parsimonious consistency with the evidence and with other accepted theories." That appears to be talk of coherence or consistency, not simplicity or parsimony.

My use of "parsimonious" is in fact quoted here, so I don't understand how my quote doesn't constitute "talk of [..] simplicity or parsimony".  I don't understand why one's criteria for truth must be either coherence/consistency or simplicity/parsimony but not both.

The aesthetic remarks of Weinberg can be found in others of more philosophical sophistication (e.g., Kuhn). The preference for Copernican astronomy over Ptolemaic resulted in a shift (if Kuhn is correct in _The Copernican Revolution_) prior to there being any empirical consequences where the Copernican model got the right answers and an appropriately epicycle-adjusted Ptolemaic model did not--this is the aesthetic preference for simplicity of which Koons speaks.

It is indeed a preference for simplicity, but I see no demonstration here that the beauty in question is independent of the simplicity/parsimony.  Such a demonstration is also absent from the examples in Koons' paper (and from the examples in the cited paper by Papineau). Without such a demonstration, Koons' argument fails to establish its conclusion.

It appears that Holtz and Koons are not talking about the same thing. Koons' argument is based on his claim that the use of the simplicity criterion needs to reliably produce truths, and it appears to me that as Koons defines it, the simplicity criterion is not part of the definition of truth.

And that is his mistake, as I explain in the three paragraphs beginning "Koons seems mistaken about the role parsimony plays in determining truth".

Koons explicitly addresses two views of implicity:

1. That the simplicity criterion does reliably yield truths. (This doesn't mean that it is an empirical conclusion rather than a methodological assumption, but only that it is subject to test.)

That "unmarried men reliably yields bachelorhood" is subject to testing of a sort, but such testing is somewhat pointless unless one denies that unmarried maleness is included in the definition of bachelorhood.  To talk of "yielding" and "testing" here is indeed to deny that simplicity is a methodological assumption.

I agree with Koons that pragmatism (ease of representation, calculation, etc.) is a poor reason for scientists to prefer simpler theories over complex ones -- just as illumination is a poor reason for a drunk to seek his missing car keys only under the streetlight. However, I think that something like pragmatism is a very good reason for epistemologists to prefer simplicity over complexity in the definition of truth.

Holtz writes that "Weinberg's rapture does not constitute a convincing argument for anything other than the proposition that parsimony works"--works how? In producing true theories, or producing formulae that get the right answers?

Neither.  If we had a prior way of recognizing "true" or "right" that didn't rely on parsimony, then we wouldn't need parsimony to decide what class of explanations to consider "true" or "right".  When I say "parsimony works", I mean just that using parsimony in our definition of truth yields more satisfaction -- we do a better job of procuring food and shelter, we get hit by fewer cars when crossing the street, etc.

On the level at which I endorse pragmatism, the alternative to it is not realism, but masochism. (See below.)

On my account, it makes as much sense to say parsimony produces truth as to say that unmarried maleness produces bachelorhood. I don't say that parsimony produces true theories; rather, I say that using parsimony as a criterion for truth is the theory-evaluating strategy that maximizes utility/pleasure/satisfaction.

I haven't had a chance to read Holtz's review yet, but I think I can pick up the drift from your quotation from it.  I dealt with this objection in the original paper in section 7, on pragmatic accounts of simplicity.  If one argues that our preference for simplicity is merely "methodological", having nothing to do with its reliability as an indicator of truth, then this is what I called a "pragmatic" justification for simplicity.

The "pragmatic account of simplicity" that Koons argues against is something like this:

X. Simplicity picks out theories that are easier for humans to represent/compute/etc. and that may thus be more useful than complex alternatives, but in doing so simplicity leads us to local maxima that do not reliably correspond to final truths about ultimate reality.

As an alternative to thesis (X), Koons effectively asserts

K. Simplicity picks out theories that reliably turn out to be true [by some criterion of truth that presumably does not include simplicity].

The problem with thesis (K) is that there is no sensible criterion of truth that doesn't include simplicity.  The counterfactual in my paper suggests that omitting simplicity from the criteria for truth leads to absurdity. To disagree with Koons one need not assert (X), but rather:

Such an account is incompatible with a naturalistic account of either scientific _knowledge_ or the _semantics_ of scientific theory, construed as about the real world.

This criticism indeed applies (at least to a certain extent) to thesis (X), but not to thesis (H).  The "real world" tends to reward one for choosing a worldivew based on parsimonious consistency with evidence (i.e. truth), and tends to punish one for choosing otherwise.  This arrangement is not a coincidence; it does not suggest a supernatural arranger. Rather, it is entirely to be expected that there be a best practice for thinkers to adopt in thinking about the world and that thinkers under selective pressure tend to adopt that practice.