[for a brief explanation of this ongoing series, as well as a full table of contents, go here]
What is naturalism, anyway?
As we have seen, one cannot talk about naturalism in 20th century philosophy (and beyond) without paying dues to Quine’s fundamental, one would almost want to say game changing, influence. And the reason to talk about naturalism at all in the context of the current project is that the “naturalistic turn” in (analytic) philosophy represents a crucial piece of the puzzle of how modern philosophy sees itself and its relationship with science. This, finally, is pertinent to my attempt at understanding how the two fields can be said to make progress, albeit in different senses of the term.
Perhaps not surprisingly, however, a “turn to naturalism” means different things to different people, and that’s even without considering the various outright rejections of naturalism that have been voiced and continue to be voiced by a number of philosophers. Before proceeding, then, I shall make my own position clear: I agree with Ladyman and Ross (2009) when they characterize any philosophy that does not take science seriously as “neo-Scholasticism.” This, given the bad reputation of Scholasticism in contemporary philosophical circles, may seem unduly harsh, but I actually think it hits the nails exactly right. Scholastic philosophers (Kretzman et al. 1982) carried out a lot of logically rigorous work, but their efforts had comparatively limited lasting import precisely because they assumed a number of notions that turned out to have little, if any, scientific traction. It isn’t that the Scholastics were not clever or interesting, once one bought into their basic assumptions about the world; it’s that their basic assumptions about the world were far off the mark, thereby making their philosophy increasingly less relevant in the long run. The difference between the original Scholastics and what Ladyman and Ross term the neo-variety (explicit examples to be found in the first chapter of their book) is that the former did not have the results of the scientific revolution at their disposal, while the latter do. Therefore, to indulge in neo-Scholastic philosophy these days is the result of a willful, and in my mind misguided, rejection of science. As far as I am concerned, therefore, the dilemma standing in the way of modern philosophy is not whether to do without science (that is simply not a viable option anymore, if it ever was), but how exactly to take on board science and whether this means a renunciation of the project of philosophy altogether (as one may read Quine as advocating, at the least implicitly, at times) or rather its modification and amplification along new directions of inquiry (which I happen to think is the most promising path to take).
Let’s go back first to the already mentioned paper by E. Nagel (1955) and his commentary on naturalism. Nagel defines it not in terms of a particular theory of nature, but as a philosophical stand based on two theses: “the existential and causal primacy of organized matter in the executive order of nature” (1955, 8) and the idea that “the manifest plurality and variety of things, of their qualities and their functions, are an irreducible feature of the cosmos, not a deceptive appearance cloaking some more homogeneous ‘ultimate reality’ or transempirical substance” (1955, 9).
Nagel doesn’t commit naturalism to the strong claim that only what is material exists, for instance mentioning exceptions that include modes of action, relations of meaning, plans and aspirations. All these things “exist” in some important sense of the term and yet are not material (though of course they have a material basis, meaning that it is not possible to conceive of any of them without a physical brain getting involved in the process). But what he does explicitly exclude from the naturalistic standpoint are things like “disembodied forces … immaterial spirits directing the course of events … the survival of personality after the corruption of the body,” that is, precisely the sort of entities the Scholastics assumed were part and parcel of the fabric of reality.
We have seen when discussing Quine that Nagel explicitly states that naturalism does not exclude other philosophical standpoints by fiat, but that nonetheless naturalism is the one standpoint overwhelmingly favored by the available evidence. That may sound suspiciously circular to critics of naturalism, though. After all, naturalist philosophers rely on the empirical evidence provided by science, and the empirical methods of science themselves assume a naturalistic framework, thereby stacking the deck against any form of non-naturalism.
There actually is a vibrant discussion in current philosophy of science about the extent to which science is automatically committed to philosophical naturalism, with people like Pennock (2011) forcefully arguing that it is, and others (Boudry 2013) responding with arguments that are very much in line with Nagel’s early insight. For the latter the logical-empirical method does not a priori exclude non-naturalistic phenomena, as long as they make some kind of contact with empirically verifiable reality: “There must be some connection between the postulated character of the hypothetical trans-empirical ground, and the empirically observable traits in the world around us; for otherwise the [non-naturalistic] hypothesis is otiose, and not relevant to the spatio-temporal processes of nature” (p. 13). Or to put not too fine a point on it: otherwise we return to full fledged Scholasticism. The basic idea, therefore, is not that naturalism excludes, say, transcendental feelings or mystical experiences a priori, but rather that a naturalist will not treat those feelings and experiences as any kind of evidence of a transcendental realm. They are far more parsimoniously interpreted as byproducts of the way in which the human brain responds to certain physical-chemical conditions (like stress, self-imposed abstinence from food, deep meditation or prayer, exposure to hallucinatory substances, and so on).
Two authors who have more recently commented insightfully on naturalism in philosophy are Laudan (1990) and Maffie (1995). Since their comments speak more closely to Quine’s concerns about the relationship between science and philosophy, and in particular about the status of epistemology, they are especially relevant to my project here. Laudan recognizes that “naturalism” actually refers to a variety of positions, but that “on the intellectual road map, naturalism is to be found roughly equidistant between pragmatism and scientism” (1990, 44). He then immediately moves to the issue of epistemology: “Epistemic naturalism … holds that the claims of philosophy are to be adjudicated in the same ways that we adjudicate claims in other walks of life, such as science, common sense and the law … it holds that the theory of knowledge is continuous with other sorts of theories about how the natural world is constituted” (1990, 44).
Pausing for a moment here, we can recognize that Laudan’s position is in important respects analogous to Quine’s. Recall from our discussion above that for Quine too there is no fundamental, qualitative difference between the way in which scientists and philosophers operate epistemically, and indeed there is no difference between either of those and the way in which rational human beings operate either. In fact, it would be bizarre if philosophers (or scientists, for that matter) could claim some special power of insight into the world that nobody else has access to (that would make them mystics, I suppose). But I think that agreeing that philosophy is sufficiently distinct from science (and both are distinct from commonsense) simply does not require such an extreme view, as both Laudan and Maffie clearly articulate. Neither of these authors, then, agrees wholeheartedly with Quine’s attempt to almost erase such distinctions. Laudan in particular refers to Quine’s view of methodological strategies as “Spartan,” being essentially limited to a combination of hypothetic-deductivism and the principle of simplicity. Laudan goes on to say that there is a place for normative considerations in a naturalized epistemology, which for him implies that epistemology does not simply reduce to psychology. While Quine was inclined to think of the decision to give up any philosophical claims to prescriptive epistemology as boldly biting the naturalistic bullet, Laudan counters that it is “more akin to using that bullet to shoot yourself in the foot” (1990, 46), a sentiment — I must admit — that has often accompanied my own readings of Quine. Laudan suggests instead that a “thoroughly naturalistic approach to inquiry can, in perfectly good conscience, countenance prescriptive epistemology, provided of course that the prescriptions in question are understood as empirically defeasible.” (1990, 46). The basic idea, I take it, is that epistemologists can continue in good conscience, qua philosophers, to do what they have always done: critically reflect on the various means to acquire and verify knowledge; and they can keep writing prescriptively (as in “this and that are good/sound epistemic practices; those and others are bad/unsound practices”), as long as they are willing to revise their positions whenever pertinent empirical evidence comes their way. But at its best philosophy has always been able to incorporate and reflect on pertinent empirical evidence, without doing so somehow turning it into a straightforward (in this case cognitive) science.
Maffie (1995) mounts yet another reasonable defense of naturalistic philosophy — one that can be read, again, as a reaction to Quine — against what he refers to as “the fallacy of scientism.” Maffie’s model is one of “weak continuity” between epistemology and science. The basic idea is to deny a number of misguided tenets about epistemology: i) that it employs norms and standards that are somehow “higher” than those of science; ii) that it uses a priori methods of evidence of a special kind; iii) that it proceeds in a way that makes no use of the findings of science; iv) that it yields firmer epistemic results than science; and v) that it is somehow prior to any science. All of the above while at the same time affirming that epistemology does employ evidential concepts, norms and goals distinct from those of science. How does Maffie manage to accomplish that?
He puts it this way: “that there is no epistemologically higher or firmer ground than science from which to criticize science does not entail that there is no epistemologically independent ground from which to criticize science” (1995, 4). That is, while defending the old fashioned model of philosophy somehow hovering above all other fields of human knowledge — including science — is untenable, it is simply not the case that the only other available model is the Quine-inspired one of subsuming philosophy into science. Maffie’s suggestion is similar to Laudan’s in this respect: philosophy can (should) keep using its standard tools — like conceptual analysis, “intuition” and reflective equilibrium (more on all these and others near the end of this book) — as long as they are not aloof but integrated with “a posteriori” practices (i.e., squared with the pertinent factual evidence). To put it differently, while for Maffie scientistically oriented naturalist philosophers elevate practicing scientists to a model to be emulated for how to do philosophy in general and epistemology in particular, weak continuity naturalists “look to the critical practices of reflective human beings” more broadly construed (1995, 4). This leads to a view of epistemology as a parallel, independent discipline that can (and should) analyze and when necessary criticize the claims made by science. Science does not get, to put it as Maffie does, “both the only say and the final say” (1995, 19).
Finally, we need to consider yet another way of approaching the issue of naturalism in philosophy, and that’s the distinction — the implications of which have been surveyed by Papineau (2007) — between ontological and epistemological naturalism.  Beginning with ontological naturalism, the basic idea is that a modern account of causality has to be rooted in scientific concepts, thus excluding, for instance, the old philosophical possibility of mental causation as a distinct category from its physical counterpart, a la Descartes. Since biological, “mental” and social phenomena all cause physical effects in the world, those effects have to fall within the limits imposed by a scientific understanding of causality. This doctrine is sometimes referred to as the principle of “causal closure” (e.g., Vicente 2006), which in its broadest formulation essentially says that any physical effect must have a physical cause. Of course, even if one accepts the principle of causal closure, there is still room for a varied ontology of the world that includes “objects” that do not per se have physical effects, such as mathematical, modal and possibly normative claims.
Echoing the comments from Nagel (1955) that I have examined above, Papineau points out that naturalism is not a rigid a priori doctrine (something to which naturalists are often accused of adhering to), because it has changed through time in response to the best scientifically informed understanding available. For instance, Descartes-style “interactive dualism” seemed dead for a while, as Leibniz concluded, but became again a live option with Newtonian mechanics and the concept of action at a distance. As is well known, it has lost viability again since then, but one cannot exclude yet another comeback, as remote as that possibility seems at the moment.
A more nuanced question is that of the relationship between naturalism and physicalism. Papineau agrees that there is room for debate here (and so does Fodor, in his influential paper on special sciences: 1974). For instance, although naturalism requires that if a mental state (say, anger) has physical consequences, that mental state has to be the result of physical processes, stronger claims like the one made by type-identity theorists in philosophy of mind (Rosenthal 1994), that thinking about a number is identical with a particular physical property of your brain, go too far and are in fact implausible because different brains could produce similar thoughts by different physical routes (an idea referred to as multiple realizability). Which raises the mandatory issue of supervenience: “Non-physical properties should metaphysically supervene on physical properties, in the sense that any two beings who share all physical properties will necessarily share the same non-physical properties, even though the physical properties which so realize the non-physical ones can be different in different beings” (Papineau 2007). The important point to take home here is that a modern naturalistic philosophy is, in this framework, a philosophy that is committed to a broad (and revisable) understanding of ontological naturalism.
An equally interesting discussion pertains the type and scope of methodological naturalism. Here Papineau draws a sharp contrast between methodological naturalists who see no fundamental difference between science and philosophy (again, a la Quine), and methodological “anti-naturalists” who do (as, I imagine, anyone strongly opposed to the approach characteristic of analytic philosophy). I think he is a bit too quick here, as a model along the lines of what Maffie calls “weak continuity” makes more sense to me. Indeed, Papineau immediately softens the allegedly sharp dichotomy: “even those philosophers who are suspicious of science must allow that philosophical analyses can sometimes hinge on scientific findings — we need only think of the role that the causal closure of physics … play[s] in the contemporary mind-body debate. And, on the other side, even the philosophical friends of science must admit that there are some differences at least between philosophy and natural science — for one thing, philosophers characteristically do not gather empirical data in the way that scientists do.” I think the latter is still too weak, since it’s not just that philosophers do not gather empirical data (besides, see my discussion of so-called “experimental philosophy” in the last chapter of this book), it’s that the concerns, tools, and attitudes of philosophers qua philosophers are partially distinct from those of scientists qua scientists.
Again, it is Papineau himself that provides reasonable ammunition for a weak continuity view of the relationship between science and philosophy: “Think of topics like weakness of will, the importance of originality in art, or the semantics of fiction. What seems to identify these as philosophical issues is that our thinking is in some kind of theoretical tangle, supporting different lines of thought that lead to conflicting conclusions. Progress requires an unravelling of premises, including perhaps an unearthing of implicit assumptions that we didn’t realise we had, and a search for alternative positions that don’t generate further contradictions. Here too empirical data are clearly not going to be crucial in deciding theoretical questions — often we have all the data we could want, but can’t find a good way of accommodating them” (Papineau 2007).
Those last few sentences, I think, really get to the heart of the matter. First off, notice the unabashed (and welcome!) acknowledgment that philosophy does, in fact, make progress. Second, Papineau points out that philosophical problems are characterized by a type of interesting empirical underdetermination: if an issue can be settled entirely on empirical grounds, then it squarely belongs to science and philosophers have very little business butting in. Third, and by the same token, philosophical discussions are not going to be independent of science-provided empirical evidence, on penalty of falling back once more into neo-Scholasticism. Lastly, Papineau sees, and I agree, philosophy’s goal (or at least one of philosophy’s goals) as that of conceptual analysis and clarification. That’s because the best philosophy is based on an effective deployment of formal and informal logic, it is a way of thinking and reflecting about issues, not a way of gathering empirical data about those issues.
Having laid out so far the bases for a reconstruction of the nature and tools of philosophy, over the next two chapters we will move to briefly examine different examples of progress in fields that bear distinct types of resemblances to philosophy: science — often, and justly, seen as the paragon of a progressive field; mathematics — which equally uncontrovertibly presents us with a picture of progress, perhaps even more clearly so than in science, and yet where progress is achieved by substantively different means; and logic — where progress has certainly occurred, but in a way that is distinct from (if similar to) the one characterizing math. We will then move to the crucial issue of whether and how philosophy itself makes progress, by way of an analysis of three specific areas of philosophical inquiry.
 As Papineau himself clarifies, this is not the same distinction that is often brought up in discussions of whether science can test supernatural claims. In that context, ontological (sometimes referred to as “philosophical”) naturalism is the philosophical position that there is no supernatural realm, while methodological naturalism is the provisional assumption — necessary for doing science, according to many — that even if the supernatural exists it cannot enter scientific theorizing at any level, on penalty of giving up the very meaning of scientific explanation.
Boudry, M. (2013) Loki’s Wager and Laudan’s Error. On Genuine and Territorial Demarcation. In: M. Pigliucci and M. Boudry, The Philosophy of Pseudoscience: Reconsidering the Demarcation Problem. University of Chicago Press, 79-98.
Fodor, J. (1974) Special sciences (Or: the disunity of science as a working hypothesis). Synthese 28:97-115.
Kretzmann, N. et al. (eds.) (1982) The Cambridge History of Later Medieval Philosophy: From the Rediscovery of Aristotle to the Disintegration of Scholasticism, 1100–1600. Cambridge University Press.
Ladyman, J. and Ross, D. (2009) Every Thing Must Go: Metaphysics Naturalized. Oxford University Press.
Laudan, L. (1990) Normative naturalism. Philosophy of Science 57:44-59.
Maffie, J. (1995) Scientism and the independence of epistemology. Erkenntnis 43:1-27.
Nagel, E. (1955) Naturalism reconsidered. Proceedings of the American Philosophical Association 28:5-17.
Papineau, D. (2007) Naturalism. Stanford Encyclopedia of Philosophy (accessed on 26 June 2012).
Pennock, R.T. (2011) Can’t Philosophers Tell the Difference between Science and Religion? Demarcation Revisited. Synthese 178:177–206.
Rosenthal, D.M. (1994) Identity Theories. In: S. Guttenplan (ed.), A Companion to the Philosophy of Mind. Blackwell, 348–355.
Vicente, A. (2006) On the causal completeness of physics. International Studies in the Philosophy of Science 20:149-171.