Naturalism is a cheap position – almost any metaphysical thesis seems to count as a version of naturalism, properly qualified. For instance, one might call me a Crypto-Naturalist (I recently was!) and be perfectly fine. Crypto-Naturalism would be the thesis that all the things the best theories of science say are existent, exist. Contrast this with what might be called Naturalism-simpliciter (although, as I just said, this is cheap): where it is the thesis that all and only all the things the best theories of science say are existent, exist. Crypto versions still count as naturalism since they do not deny that science tells us what exists – nor do they deny that we should trust our best scientific theories, as many Naturalists seem to think people like me say. It merely denies the “only” part.
So, Naturalism seems to have something to do with science, but what? Is naturalism an epistemic (methodological) thesis, saying we (philosophers) should follow the methodology of science? Some Naturalists are nominalists – but scientists do not care about nominalism! So, are these naturalists Naturalists? Scientists seem to believe in numbers, so should the rest of us too? Scientists posit as many relations and properties as they need to explain theory and data – should we too? If we philosophers follow the methodology of scientists we will believe in many strange and marvelous entities that we might not desire to believe in. And, if we don’t, how are we naturalists? Or, is naturalism a metaphysical thesis – saying that we should take our cue to metaphysics from physics? If it is this, what evidence do we have (on scientific grounds!) that the scientists are correct? After all, many of the most brilliant disagree – and plausibly will continue to disagree – over what they seem take the basic structure of existence and existents to be.
Why should we think that our best scientific theories capture all of reality? Why should we think they tell us anything interesting about existence itself? Aha! So here seems to be a fundamental feature of Naturalism: the denial of First Philosophy. First Philosophy – that venerable and ancient tradition – says that metaphysics precedes physics. The First Philosopher (i.e. non-Naturalist) says we must do philosophical work on the basic ontological structures and categories before we can do science, because even the scientists must take basic ontological commitments for granted. Physics tells us that this and this exists, etc, but metaphysics tells us what is possible, necessary, contingent, and the basic ontological categories that all existent entities fall into. Notice that one can be a First Philosopher and also a Crypto-Naturalist: there is nothing wrong (in fact, it’s good) in believing what the best theories of science say, but those best theories would be begging the question if they also say they are the final word. That final word must come from First Philosophy. So, in that sense, the Crypto-Naturalist is also a perfectly good Non-Naturalist.
As the blog Common Sense Atheism puts it: “Most philosophers are naturalists. Because naturalistic science has been more successful in a few centuries than the metaphysical speculations of philosophy have been over several millennia, most philosophers are eager to develop an understanding of all phenomena as natural phenomena, including things like human consciousness and ethics.”
What they don’t put, however, is that this is very cheap. In fact, I can confidently say that I am a naturalist about phenomena, ethics, consciousness, etc and still be a Crypto-Naturalist in good standing. And this is precisely because of First Philosophy. After all, what are phenomena? What counts as natural as opposed to unnatural phenomena? What is consciousness? What counts as conscious experience, such that it has irreducible qualitative features to it? Can rocks have consciousness, even if they do not have neurons? (That’s not something our best scientific theories can answer!) And, natural properties aside, what counts as ethics such that we try to find certain natural moral properties? To answer any of these, plus the myriad other rather important questions science must assume answers to (e.g. what is possible, contingent, necessary, actual, concrete, abstract, time/tensed, etc) we must first have metaphysics.
So I say: naturalism, fine. All well and good, but give me the Crypto version – it seems more sane and by far less question begging. Let us not take by hook and crook what other philosophers gain by honest toil.