Suppose you're a non-theist of the thoroughly secular sort: not only is there no theistic god, but neither is there a deistic god; nor are there any finite gods or a world spirit, or anything of that sort. There is just the natural world. Must you thereby be a materialist? That is, must you believe that everything is composed of matter in the old-fashioned sense? To put it more formally, consider the following strict conditional, which I shall call 'Naturalism Entails Materialism' (NEM for short):
(NEM) Necessarily, If naturalism is true, then materialism is true.
Now my question is this: is NEM true? If it is, then this isn't obvious. I've argued in a previous post that naturalism is compatible with the existence of abstract objects. That is, naturalism is compatible with the existence of immaterial, necessarily existent, non-spatiotemporal entities (I also argued that traditional theism is *incompatible* with the existence of abstract objects in that previous post). For naturalism is only committed to explaining things *that need explaining* in terms of the natural world. But if abstracta are necessarily existent, then they need no explanation. Thus, since naturalism is compatible with the existence of abstract objects, then since such a view is incompatible with materialism, we *already* have a sufficient reason to reject (NEM).
However, I want to argue here that (NEM) is false for reasons independent of this. For naturalism doesn't entail that the ordinary spatiotemporal world of visible objects is wholly "physical" in some crude sense. For naturalism is compatible with the view that ordinary substance has an immaterial aspect as a part of its essence. Read Spinoza and Bertrand Russell, for example. Or, more recently, read Daniel Stoljar and David Chalmers. According to past and contemporary philosophers such as these, matter may well be different from what we imagine. For example, think of material substance as having, *as part of its essence*, *both* material *and* immaterial attributes. Or think of substance as being, at the most fundamental level, *neither* mental *nor* material, but the stuff out of which both matter and mind are *derived*. If these views are coherent and plausible (and I think at least a few of them are), then we have more reason to think that (NEM) isn't a necessary truth.
Ok, but what's the big deal? This. It's common for Christian apologists to say that if one is an atheist, then one must be a naturalist, and that if one is a naturalist, then one must be a materialist (in the sense that the material objects, and the properties of them studied by the sciences, are all there is). And if this is so, then it's very hard, if not impossible, to account of the existence of a number of things. For example, abstract objects and consciousness. Now as I've argued in the previous post mentioned earlier, it's not true that a naturalist can't account for abstract objects (or more carefully, we don't *need* to account for them, if by "account" one means "explain". For abstract objects are necessary existents, and as such, they don't *need* an explanation in terms of something beyond them).
But in light of the present post, we see that it's much, much easier to account for consciousness as well. For while it may be very difficult to account for consciousness in terms of our ordinary conception of matter and its properties, if *any* theory like the sorts mentioned above is coherent, then one can say that the fundamental features of natural objects have what it takes to give rise to consciousness, as proto-mental facts are *basic* features of natural objects. In fact, such theories make it easier to account for the interaction between mind and body than substance dualist theories typically espoused by Christians. For unlike the latter view, the former sorts of views don't have two fundamentally different sorts of substance trying to interact. Rather, you have both material and "mental" aspects inhering in a *single* kind of substance.
Thus, being a naturalist does not thereby commit one to being a materialist. For on the sorts of theories of substance mentioned here, it's *true* that the *natural* world is all there is, but it's *false* that the *material* world is all there is. But if so, then in addition to the argument in my previous post about the compatibility of naturalism and the existence of abstract objects, we have yet another reason to think that (NEM) is false.
In light of this post and the previous, it is I hope very clear that Christian apologists have their work cut out for them. It will not do to just point to certain sorts of phenomena -- such as abstracta or consciousness -- and say that these are difficult or impossible to account for on a materialistic account of the world. For a naturalist can *grant* all of this, at least for the sake of argument, without batting an eye. For again, as we've just seen, naturalism isn't wed to materialism. Materialism may or may not be sufficient to explain all the phenomena that needs explaining (the jury is still out on that one). But the theist assumes that if it is *not* sufficient, then we should add to our ontology of material substance a god or two to get the explanatory work done. But what *I'm* saying is that there is a less radical and more economical response to such a situation: instead of *adding* a new kind of substance to our ontology, why not merely *modify* our *existing* theory of substance so that it *is* sufficient?
This completes my posting on the relationship between non-theism, naturalism, and materialism. The moral is that Christian apologists are aiming at the wrong target: they need to take aim at *naturalism*, not *materialism*. Unfortunately, naturalism is a tougher explanatory ship to sink, as it has a vastly larger warehouse of conceptual resources to draw from.