… What is wrong, according to most philosophers, with souls and vital fluids? One of their central defects is their being immaterial. There are perfectly respectably immaterial entities — concepts, numbers, or hypotheses, for example — but souls and suchlike are not the right kinds of things to be immaterial. Part of the reason for this is that they are taken to be subjects of causal agency, and immaterial causes are seen as contravening naturalism. This is not an entirely straightforward matter. One might well claim that the concept of evolution, or of class struggle, had changed the world. But I think it is fairly clear that we don’t want to treat this as the exercise of a causal power by an entity, or at any rate we don’t if we are any kind of naturalists. I’m not exactly sure why we feel this way. Perhaps the answer is that knowledge of causality does, as a number of influential philosophers have argued, derive ultimately from our material transactions with things. Even for material things that are much too small for us to interact with, there is considerable force in Ian Hacking’s much-cited remark about electrons: if you can spray them they are real. Perhaps there is a cruder picture here, that nature is ultimately composed of material things pushing and pulling at one another. Pushes and pulls from outside this material universe are just the sorts of supernatural interventions that naturalists rule out. At any rate, I propose to take for granted that there is something importantly fundamental in our ontology about material things, material here merely in the Cartesian sense of things that occupy space, albeit sometimes, like electrons, not very much, or like gases, not very fully. Being in the same space as we are is, of course, a minimal condition of being in a position to engage with us in pushings, pullings, and sprayings.
Important threats to this ontological primacy of space occupiers have come from physics. Physics tells us about fields that, while they have particular strengths at particular locations, don’t appear to occupy the locations where they occur. And worse, quantum mechanics tells us that what might have seemed like the most fundamental space occupiers, physical particles, are actually not, from some perspectives, particles at all, but waves, which are apparently not space occupiers at all. These claims are particularly important to the contemporary naturalistic philosophy that I am here considering, because most contemporary naturalists include among the central commitments of naturalism not materialism, but physicalism. The move from materialism to physicalism, in large part motivated by such developments in physics, aimed to avoid being committed to a long-superseded broadly Newtonian physics. Physicalists instead committed themselves to take whatever physicists ended up saying about the nature of reality as an ultimate ontological criterion for reality. If the ultimate constituents of reality couldn’t make up their minds whether to be particles or waves, or turned out instead to be ten-dimensional bits of string, so be it.
I have, naturally, no objection to allowing physicists whatever authority there is to be had about the ultimate structure of matter. What might be a worry, however, is whether physicalism, as just described, is in the same line of business as the materialism it has replaced. Materialism, as I introduced it, was part of the expression of anti-supernaturalism. If you can’t kick it, or at least spray it, you should treat it with some suspicion. We can kick things or spray them because they live in the same space as we do, and there is nothing and nowhere else. Materialism is, of course, also contrasted with dualism, a specific form of supernaturalism, and a doctrine that explicitly insists on the existence of things that are not in the space of electrons, stones, and ourselves, and in most versions insists on the causal efficacy of such things.
… Very summarily, naturalism is explained in terms of anti-supernaturalism, which is in turn cashed out in terms of materialism; the developments or radically new conceptions of matter by the physical sciences leads from materialism to physicalism; and physicalism is often understood as entailing monism.
I don’t propose to explore in great detail these routs from naturalism to monism. Rather, I want to emphasize a quite different philosophical commitment often associated with naturalism: empiricism. And what I want to claim is that the move to monism violates this commitment. Monism, far from being a view of reality answering to experience, is a myth. And myths are just the sort of thing that naturalism, in its core commitment to anti-supernaturalism, should reject.
… While my ultimate target in this chapter, monism, is a metaphysical thesis, as I have just indicated a main bridge from naturalism to monism is through a commitment to the explanatory reach of science. If this is combined with the idea that science is a largely continuous and homogeneous activity, and even more specifically that its explanatory resources depend on its sole concern with the material structure of things, then we are well on the way to naturalistic monism. But monism, I claim, is a myth. And it is a myth that derives what credibility it has from its connection to another myth, the unity of science. So I shall now explain in some detail why this latter doctrine, the unity of science, is indeed a myth.
… myths are, minimally, false stories that serve often central and important functions in the lives of their adherents distinct from stating how things are. This is the sense in which the unity of science, I hold, is a myth.
… How could the sciences be, in any sense, all about the same thing? The simple answer, and one that is still quite widely accepted, is that the only science, ultimately, is physics, so that all the sciences are really about whatever physics is about. The classical version of this doctrine is the doctrine of physicalistic reductionism. According to this theory, the sciences should be thought of as arranged in a hierarchy, with particle physics at the base, then (perhaps) chemistry, molecular biology, and organismic biology, and at the top ecology and the social sciences. All sciences other than elementary particle physics were to be reduced to the next lowest level in the hierarchy by characterizing the entities with which they dealt in terms of their structural make-up, and deriving the behavior of those entities from the laws governing the structural parts of which they were made. Ultimately, therefore, everything was to be understood as an arrangement of elementary particles and the behavior of everything was to be derived from the laws governing the behavior of such particles.
As an account of the real workings of science, this picture has been widely, though by no means universally, abandoned. But its spirit has by no means been abandoned, and indeed continues to govern thinking in central areas of philosophy.
… consider the prima facie absurd proposal of a number of contemporary philosophers that we should replace talk of the mind with talk of bits of the brain. This remains absurd on more careful reflection. The problem is simply that to replace mind talk with brain talk requires that the latter can serve the purpose of the former. But it is exceedingly unlikely that this is so. Even if, in some sense, we are talking about the brain when we refer to features of our mental lives, there is not the slightest reason to believe that, say, my belief that the US stock market will crash soon can be identified with some well-defined part of my brain; still less that the same part of my brain will consistently correspond to just this belief; and least of all that everyone has a structurally identical part of their brain if, and only if, they believe that the US stock market will crash soon. And it seems that it is this last that would be needed if there were to be some piece of brain talk with which, in principle, one could replace this bit of belief talk. (I suggest, indeed, that this is a place where the supernatural qualities of monism appear clearly. Magical powers are being attributed to brain cells on the basis of no empirical evidence, merely from metaphysical commitment.)
… Despite the absurdity of taking this replacement talk seriously, it is clear what is the intuition underlying it, and this is an intuition that seems far from absurd to most philosophers. This is the idea that whatever we may say about beliefs, intentions, and the like explaining or even causing our behavior, there is also a set of physical causes that must simultaneously fully explain our physical movements. This brings us, finally, to the doctrine of the completeness of physics. A remarkable amount of contemporary work in the philosophy of mind, in the philosophy of biology, and in the philosophy of the social sciences is concerned with the attempt to reconcile the assumed completeness of physics with the perceived failure of attempts to reduce higher-level science in the direction of physics. One solution is the eliminativism I have just been discussing, the view that the march of science will eventually sweep away the vocabularies of biology, folk psychology, or sociology. A more modest solution is the instrumentalism defended by those who admit that we cannot, perhaps for reasons of principle, get by without biology, psychology, or the social science, but add that since the entities of which these sciences speak are incommensurable with those of physics, the former cannot be recognized as ultimately real.
A much better solution, it seems to me, is to abandon the dogma of the completeness of physics, together with the doctrine of the unity of science that it underpins. Let me mention a few reasons why we should be happy to abandon this dogma. Foremost among these is the commitment to empiricism insisted on earlier in this essay, and the observation that there is essentially no evidence for the completeness of physics. We can begin to see this by noting the extent to which the failure of reductionism in various crucial areas of science undercuts the plausibility of the completeness of physics. There are, of course, no actual accounts of the behavior of mice or men, or even bacteria, as flowing from the physical properties of their smallest physical parts; and no such accounts appear to be in the offing as reductionist science develops. The belief that such an account must exist in principle, or in the mind of God, is at best an inference from what we do know about the behavior of systems simpler by many orders of magnitude, and hence an inference that goes beyond any decent empiricist strictures. It is, in short, a supernaturalist belief.
It will be said that these simpler systems give us knowledge of laws of nature, and these laws can then (in principle) be applied to far more complex systems. But what could possibly license this extension in the admitted absence of any direct evidence for the applicability of the laws to these more complex systems? As Nancy Cartwright pointed out many years ago, even as apparently simple and robust a law as the law of universal gravitation only applies to situations in which no other forces (electromagnetism, for example) are acting. Naturally, we have good procedures for dealing with some situations in which there are forces of different kinds acting. But it is still the case that the principles by which we combine different forces are principles distinct from and additional to those laws describing the sources of specific forces.
… The universe-wide microphysical machine, the integrated realm of microscopic particles that forms the substance of reductionist fantasies, is not a product of naturalistic enquiry, but a supernatural construct of the scientific dreamer. Naturalists should reject the image not just because it lacks proper naturalistic credentials, but because it violates the most basic naturalistic commitment to the rejection of the supernatural.
… our empirical experience of nature is, on its face, an experience of a huge diversity of kinds of things with an even huger diversity of properties and causal capacities. Some of these properties are open to causal inspection; others require careful, even inspired, scientific investigation. Neither casual experience nor detailed investigation suggests that all these properties are best understood through attention to the physical stuff of which things are made. The advance of science does indeed lend credence to the view that we do not need to appeal to supernatural things in explaining phenomena. One variety of supernatural things are those that are made out of non-physical stuff, like angels or Cartesian minds. So we may allow that naturalism commits us to the monism that insists that all stuff is material, even physical stuff. The corollary that insight into the properties of stuff holds the key to understanding the properties and behavior of all those diverse things that are made of that stuff is another matter altogether. And this indeed is the kind of doctrine that suggests the attribution of supernatural powers to physical stuff in a way wholly inimical to naturalism.