Petersen’s solution is as follows: Let’s think of naturalism as a commitment to the methodology of science; let’s think of science as a commitment to the model of inference to the best explanation; and let’s think of explanation as a matter of systematically boiling things down to a minimum number of brute facts. Or in Petersen’s “soundbite form”: “Naturalism is scientism is explanationism is unificationism.” Mathematics, with its axiomatic method, and philosophy, with its methods of conceptual analysis and unification via general principles, would count as “naturalistic” in this sense. Astrology, which posits unexplained relationships between celestial activity and the course of everyday human life, would not. More to the present point, naturalism itself would count as a naturalistic theory in this sense, so that the coherence problem is solved.
The trouble with this is that it makes naturalism completely trivial; in particular, it makes Plato, Aristotle, Plotinus, Aquinas, et al. all “naturalists” committed to “scientism.” Indeed, it makes their views more “naturalistic” and “scientistic” than those of most contemporary self-described “naturalists.” For Neo-Platonic arguments for The One, say, or Aristotelian-Thomistic arguments for an Uncaused Cause who is Actus Purus and ipsum esse subsistens, eliminate brute facts altogether – the ultimate cause of things, on these views, could not possibly have been other than it is – while most contemporary naturalists assume that some brute facts or other are inevitable, and the only question is how many we need to countenance.
Petersen is aware of the problem that his position seems trivial if it entails that philosophical claims collapse into scientific ones, and his solution is to bite the bullet and propose that we accept this expansion of what is allowed to count as scientific. The problem now is that while this might seem plausible if we focus only on the sorts of thinkers Petersen takes as examples of “naturalistic” philosophers in his expanded sense – Hume and Quine – it seems absurd when we consider philosophers like the ones I mentioned.
Petersen also insists that his position is non-trivial insofar as it is incompatible with any conception of “first philosophy” that would let philosophy trump empirical science when there is a conflict between the two. The trouble with this is that it attacks a straw man. No advocate of “first philosophy,” whether in the older, Scholastic understanding of this idea or in the modern Cartesian rationalist sense, believes that philosophy and empirical science can ever truly conflict with one another. It would be nice to have an instance of such a purported conflict, but Petersen does not give us one.
But let us consider, for example, Thomistic arguments for the immateriality of the intellect or Cartesian arguments for immaterial substance. Are these incompatible with any finding of empirical science? They are not, because they are not probabilistic “empirical hypotheses” which have somehow been superseded by later and better “empirical hypotheses.” Rather, they are attempts to demonstrate that the mind cannot even in principle be material, so that the immateriality of thoughts and the like is itself simply part of the data of which any empirical theory must take account. We can argue about whether or not they succeed in showing this, but in the nature of the case they cannot be said to be incompatible with any finding of empirical science, because they have to do with higher-order questions about the data from which such scientific inquiry must begin – questions Peterson himself allows as a legitimate area of philosophical inquiry on his broadened conception of naturalism.
I don’t know if Petersen would claim otherwise, but many other naturalists would, on such grounds as that (a) arguments for dualism involve “positing” something like “ectoplasm” as the most “probable” way of “explaining” human behavioral and psychological phenomena, where these arguments are held to be less compelling than the materialist alternatives, or (b) that natural science has somehow already “shown” that there are no immaterial phenomena. The problem here is that (a) is a complete travesty of what dualist arguments actually say, and (b) is invariably question-begging, and typically committed to the very sort of incoherent naturalism that Petersen rejects.
As it happens, though, Petersen is happy to acknowledge that his position so broad that it will allow even Richard Swinburne’s arguments for God’s existence to count as “naturalistic.” Many would no doubt regard this as a suicidal concession, but it is not. For Swinburne’s arguments are essentially of the family of arguments most famously associated with William Paley – arguments that take for granted a broadly mechanistic conception of nature, conceptualize God in terms used univocally both of him and of us, proceed via probabilistic hypothesis formation, etc. And as I have argued in a couple of recent posts (here and here) a sophisticated naturalist would realize that he has nothing to fear from Paley-style arguments. What naturalists really want to avoid is the God of classical theism, and as I argue in those posts, Paley-style arguments not only don’t get you to, but indeed get you away from, the God of classical theism.
What does get you to classical theism, though, are arguments informed by some variety of classical metaphysics – arguments of the sort given by Aristotelians, Neo-Platonists, Thomists, etc. That’s where the real trouble for Petersen’s position comes in, because it is so broad that it includes even these. And if metaphysical demonstrations of Plato’s Form of the Good, or Aristotle’s Unmoved Mover, or Plotinus’s One, or Aquinas’s ipsum esse subsistens count as “naturalistic,” then Petersen’s “naturalism” isn’t anything close to what contemporary naturalists think of their position as consistent with.
Or to put it another way: If Petersen’s “naturalism” has put him in the same camp with the author of The Last Superstition, then his dissertation adviser has given him some seriously bad career counseling…