If naturalism is true, then....
Really, we, meaning respectable folks who take ideas seriously and thus hope to be taken seriously, should completely stop using that protasis (I know, a less-known word, but I just learned it and am happy about that--it means the leading, or "if," part of a conditional phrase of the if..then sort). For respectable folks with respectable ideas, there is no reason to use it, and since it's an irritating distraction, we shouldn't. Everyone that uses it can wave it like a banner that tells the rest of us that they're sitting at the kids' table and don't need to have their ideas taken seriously yet.
Naturalism, despite a common error, doesn't mean going out and observing nature. Naturalism is a precise term for a philosophical position, one that suffers under one of the most unfortunate and stupid definitions going in philosophy. Naturalism is the position that "everything arises from natural properties and causes, and supernatural or spiritual explanations are excluded or discounted" (Google's dictionary). This definition is stupid and probably useless because it's obsolete, a relic of our superstitious past that should be laid upon the ash heap of history.
Now, let's develop a short defense of my case here, since I expect many respectable folks don't think it's obvious at all that we should never preface anything with "if naturalism is true, then...."
The definition is stupid
At first blush, particularly for someone trained in philosophy, the definition for naturalism seems pretty good. It's certainly cogent, and it definitely describes in clear detail a possible philosophical position that has absolutely been held by great thinkers in our past (and present). It also seems to get a lot of play since the sciences, hard and soft, and the historical method apparently subscribe to it. This subscription, in fact, is called "methodological naturalism," and it is praiseworthy when understood--and for very good reasons.
In reality, it's not a good definition at all, though, because it implies a certain closed-mindedness that is antithetical to an honest approach to the sciences and is a factor in the historical methods because we don't have any good reasons to think it shouldn't be. This is really to say that neither scientists nor historians are dogmatically adherent to naturalism, even of the methodological type, but are rather subscribe to it in a de facto manner. (The good reason here being that they want to have their work taken seriously by people at the adult table, as we shall discuss.)
To show that I'm not being unfair here, a good reason to reject methodological naturalism in the historical method, for instance, would be unambiguous reasons in the present to believe that anything supernatural goes on at all. We don't have any such reasons, so assuming a methodology that looks like naturalism is simply assuming a certain kind of consistency in history, as opposed to bucking what is a rock solid, unambiguous trend in the contemporary evidence. Because we have no evidence for supernatural anything now, for historians to do otherwise than to adopt methodological naturalism as a working assumption would be to make fools of themselves, frankly.
In the sciences, the matter appears a little more cloudy because many scientists will say outright that they're naturalists, though, again, I'm quite sure most are the de facto type and not dogmatically bent to it. The very existence of science is to concoct salient and usefully predictive explanations of natural phenomena, and it is cracking good at it. Of course, this is based upon a perfect track record in the
"supernatural explanations replaced by natural ones," and vice-versa, that rests fully upon the natural. How could a scientist be taken seriously if she rejected that kind of evidence in favor of unprovable speculations?
And it isn't as one-sided as the anti-naturalism crowd would suggest. Scientific efforts have plumbed a great many suggested supernatural phenomena, from ghosts to prayer to ESP to you-name-it, and so far, they've found no good reasons to suppose that the supernatural has anything to do with anything at all. That's a big point, too.
Science is about being open-minded (though not so open that one's brains fall out, to paraphrase something I know Richard Dawkins has said). Scientists committed to their craft have a commitment upon them to leave open a door, however improbable, however distantly unlikely, that some supernatural something will be discovered at some point or another. They're perfectly within their professional scope and liability, though, to treat that probability exactly as it deserves to be treated--as abysmally low, which is to say negligible or perhaps even as almost surely, or effectively, zero. Thus, there is no onus upon them to respect the positions, arguments, or beliefs of anyone insisting that they take the supernatural more seriously than a laughing, "I really don't think so."
Since the definition doesn't really describe anyone, it seems like it might be a poorly defined word that we really shouldn't be using. In that case, "if naturalism is true, then..." is revealed for what it is--the banner showing us where the kids' table is.
A better definition
A far better definition for the term, since it seems like I should offer one, would be: "naturalism is the philosophical position that, in all probability and based on everything we currently know, everything arises from natural properties and causes, and supernatural or spiritual explanations are ignored as extremely distantly remote possibilities" (emphasis indicating my changes).
Consider for a moment what that does to "if naturalism is true, then...." I rest this part of my case.
We nearly all hold naturalism on this better definition
The first thing to observe about this better definition, should we wish to dig deeper, is that religious believers are instantly identifiable as holding both naturalism and supernaturalism. That is to say that those attempting to promote belief in some aspect of the supernatural already hold all of the key beliefs that naturalism espouses plus additional ones.
Everyone, outside of the most ardent skeptics (who are not respectable people whose ideas are taken seriously) accepts some basic facts that underlie this more reasonable definition of naturalism. We all believe the world exists. We all believe that evidence is possible to obtain and useful for making sense of the world. We all believe that scientifically justified natural explanations are very good when we have them. Those who want to shuttle more into their belief structure than this sort of thing accept exactly these ideas plus additional ones about the supernatural, which is usually to say the theological.
As a brief aside, I'll note that this isn't a controversial point, and it is one supported by data. Psychologists of religion have noted that almost all (non-fundamentalist) people accept a naturalistic explanation over a religious one whenever one is available (See Hood, Hill, Spilka, Psychology of Religion: An Empirical Approach, 4th ed., p. 45). All respectable people who want to have their ideas taken seriously accept every natural explanation that they have, and wherever they refuse to accept a known natural explanation (say favoring creationism over biological evolution), they tacitly admit that those ideas do not deserve to be taken seriously by serious people.
So supernaturalism becomes the relevant term, as it should, defining those who in addition to holding a more broadly construed naturalism also hold ideas about the existence of the supernatural. In this context, "if naturalism is true, then..." reduces to the announcement of a complaint that someone else at the adult table doesn't share their fancies. They are, of course, welcome to prove anyone wrong, and for centuries now, we've been waiting (arguably too patiently) for them to do it.
Misguided musing even on the strict definition
"If naturalism is true, then..." whatever is about to be argued cannot be explained by naturalism has to be able to be explained by natural explanations somehow. Think about this and spare us the nonsense, please.
Usually this conditional is offered as some kind of a defeater, though, by suggesting something like (a recent favorite) "if naturalism is true, then we cannot account for humanness." No. Incorrect. If naturalism is true, then humanness, for example, has a natural explanation that we may or may not yet know.
Not everyone is so obviously crude in their use of the would-be defeater, though. Sometimes it's presented more along these lines: "if naturalism is true, then there cannot be an explanation for consciousness." Pause for a moment, though, and realize what is going on here. This is actually the same statement made above, generalized slightly, and despite any heap of arguments used to bolster the claim, if naturalism is true, then there is a natural explanation if it is something that can be explained.
That last qualifier I made appears to leave open a door. It doesn't. It is possible that some articles cannot be explained, cosmogenesis, the origin of the universe, being a possible candidate for this status. If it is something that cannot be explained, though, notice that positing a supernatural explanation is self-defeating.
This seems like cheating on my part, but the inherent problem with supernatural explanations, being supernatural, is that we have no way to know that they're right--so they can't really be known to be explanations. To say that something can only be explained by supernatural means, and prove it, is tantamount to saying that it cannot be explained. Of course, there's an easy objection to make here, that I'm using naturalism to discount any possibility of supernaturalism, but that's not the case. I'm just rejecting explanations that are beyond any sort of verification as being the (usually useless if about the supernatural) abstractions that they are.
"If naturalism is true, then..." just cannot be seen as an indication that we should take seriously what follows or any other ideas that are tied to it. Respectable people who want to be taken seriously shouldn't use this protasis. It's just not helpful, and it is actually worse.
It's unnecessarily distracting
What is gained by adding a qualifier of "if naturalism is true, then..." to any discussion whatsoever? A tangent, that's what, a tangent into pretending that we have to take the remotest and least supported ideas as serious ones. And we do have to get into this tangent, usually, lest we upset someone's religious insensibilities or appear incompetent to deal with what we should be able to dismiss until Sagan's still awaited "extraordinary evidence" arrives to change our minds about the matter.
This twaddling tangent always takes us afield from any serious discussion it is raised in, most commonly to the defense of religious ideas that aren't even defensible if we gave them the supernatural, and so it is a distraction. Since the word doesn't describe most honest people's position accurately, except perhaps when they're in a temper raised by having to deal with this rancorous irritation, it's unnecessarily distracting.
Saying "if naturalism is true, then..." isn't something that respectable people who want their ideas taken seriously should say. It's something that unrespectable people who want their ideas taken more seriously than they deserve say, and it takes away from everyone. We shouldn't suffer fools gladly, and those who say things like "if naturalism is true, then..." clearly show themselves to be fools not to be suffered, at least not by serious people who wish to have their ideas taken seriously.