Physicalism

 

The crudest formulation of physicalism is simply the claim that everything is physical, and perhaps that is all physicalism ought to imply. But in fact a large number of distinct versions of physicalism are currently in play, with very different commitments and implications. There is no agreement about the detailed formulation of the doctrine, even though a majority of philosophers would claim to be physicalists, and a vast majority of them are physicalists of one sort or another. There are several reasons for this lack of agreement: deep and imponderable questions about realism and the legitimacy of a narrowly defined notion of reality, questions about the scope of the term “physical,” issues about explanation and reduction, and worries about the proper range of physicalism, particularly with respect to so-called abstract objects such as numbers, sets, or properties. And while the traditional challenge of psychological dualism poses a live threat only to a few iconoclasts, the project of specifying a physicalism which plausibly integrates mind into the physical world remains unfinished, despite the huge number and diversity of attempts.

It would be natural to begin the delineation of physicalism by contrasting it with the older doctrine of materialism, but this contrast is itself vague and murky. For a great many philosophers “physicalism” and “materialism” are interchangeable synonyms. But for some, “physicalism” carries an implication of reductionism, while materialism remains a “purely” ontological doctrine (one which perhaps better respects the ancient roots of the doctrine, which wholly predates science itself). Still others invoke a contrast between the traditional materialist view that all that exists is matter (and its modes) and the modern view in which the physical world contains far more than mere matter, and in which the concept of matter has been significantly transformed. This latter sense of the term also expresses the proper allegiance of the physicalist, which is unabashedly to the science of physics: physics will tell us what the fundamental components of the world are, from which all else is constructed.

Here is the rub. How are we to understand this relation of “construction” which holds between the “fundamental” features of the world discovered by physics and everything else? Ironically, it was the tremendous growth in scientific activity in the nineteenth and twentieth centuries that forced the issue. For the sciences grew not as offshoots of physics, but rather as more or less independent, autonomous disciplines with their own domains and methodologies (especially problematic were the most recent entrants to the fold: psychology and the social sciences). For those seeking to embrace a physicalist outlook - at first mostly the vigorous and philosophically evangelical logical positivists (see logical positivism) - the proliferation of scientific disciplines demanded a reductionist reply that combined, or perhaps confused, ontological and epistemological issues. The positivist slogan to be underwritten by reduction was “unity of science,” in which scientific legitimacy was granted by tracing a discipline's pedigree back to the patriarchal science of physics (see unity of science).

In a remarkable burst of philosophical energy, marshaling modern logical technique and results, as well as a good acquaintance with science itself (especially physics), the doctrine of reductionism was quickly worked out (see reductionism). In essence, reduction permitted the translation of any statement from a reduced theory into an extensionally equivalent statement of physics. Reduction being transitive, there was no need for all theories to reduce directly to physics. Reduction could proceed step by step through the scientific hierarchy. A possible example of such a reductive hierarchy might be sociology reducing to psychology, psychology to neuroscience, neuroscience to chemistry, and chemistry to physics. The positivist theory of explanation also entailed that explanations would reduce along with their theories. Altogether, it was a pretty picture.

In part because of its virtues of logical precision and clarity, the faults of positivist reductive physicalism have become ever more apparent. Its demands on scientific theorizing are too stringent, its vision of explanation too restricted, its view of science overly logicist and formal, its treatment of the history of science naive, and its view of the culture of science hopelessly crude and rather blindly laudatory.

It is possible to take another tack, to view physicalism as a purely ontological doctrine which asserts no more than that everything is at bottom physical. Such a view leaves questions of inter-theoretic relations as questions of inter-theoretic relations. Our theories represent a myriad of distinct, though methodologically related, approaches to a world that is through and through physical; but there is no need to demand, and little reason to expect, that this myriad will align itself along the narrow line envisioned by the positivists. Some theories may so align themselves, especially if their domains are significantly overlapping, and there may be some special cases where positivist reduction can almost be achieved, such as in thermodynamics (though the extent to which this case meets the model of reduction is moot). On the positive side, this mild physicalism replaces reduction with supervenience. Specifically, supervenient physicalism requires that everything supervene on the physical, by which is crudely meant: no difference, no alteration without a physical difference or alteration. For example, though there are no prospects for reducing economics to physics, it seems plausible to suppose that there could not be a change in the bank rate without there being some physical changes which “underlie” or “ground” or, better, subvene the economic change. This doctrine is empirically plausible - we have lots of evidence that all change is dependent upon the physical structure of things. By and large, we don't understand the details of this dependency; maybe, for various reasons, including mere complexity, we will never understand the details. This need not lead us to reject a proper physicalist view of the world. Such a physicalism also imposes some constraints on scientific theorizing in that it forbids postulation of nonphysical agencies in sciences other than physics (and, in physics, the postulation of a nonphysical agency is impossible, though often enough new physical agencies are postulated which transcend the current catalog of the physical).

Of course, the extent to which the reductionist dream can be fulfilled and the limits of what could reasonably be labeled a “reduction” remain open questions. It is another virtue of supervenient physicalism that it applauds and encourages the attempts to explore inter-theory relationships; it frowns only on the absolutist dictate that all such relations must conform to a single model. Science, and the world as well, is too complicated to ground any confidence in reductionism. The primary virtue of supervenient physicalism is its acceptance of the complexity of the world and our theorizing about it, along with denial that this entails any ontological fracturing of our scientific image of the world.

Further reading
Beckermann, A., Flohr, H., and Kim, J., (eds) 1992: Emergence or Reduction: Essays on the Prospects of Nonreductive Physicalism (Berlin: de Gruyter ).
Davidson, D. 1980: Mental events . In Essays on Actions and Events (Oxford: Oxford University Press ).(The first presentation of a nonreductive, supervenient physicalism.).
Field, H. 1980: Science without Numbers (Princeton: Princeton University Press ). (An attempt to present a purely physicalist account of the use of mathematics in science.).
Fodor, J. 1981: Special sciences . In RePresentations (Cambridge, MA: MIT Press ).(Argues that anti-reductionism poses no threat to physicalism or to scientific practice.).
Hellman, G., and Thompson, F. 1977: Physicalism: ontology, determination and reduction . Journal of Philosophy , (72) , 551 64.(A well worked-out version of supervenient physicalism.).
Kim, J. 1989: The myth of nonreductive materialism . Proceedings of the American Philosophical Association , (63) , 31 47.(Disputes whether supervenience is compatible with nonreductionism.).
Nagel, E. 1961: The Structure of Science (New York: Harcourt, Brace and World ).(Classic treatise on philosophy of science with a beautiful discussion of reductionism.).
Oppenheim, P., and Putnam, H. 1958: Unity of science as a working hypothesis . In Minnesota Studies in the Philosophy of Science , (vol. 2) , ed. H. Feigl, M. Scriven, and G. Maxwell (Minneapolis: University of Minnesota Press , 3 36. (Classic statement of reductionism.).
Post, J. 1987: The Faces of Existence (Ithaca, NY: Cornell University Press (An extremely wide-ranging attempt to provide a nonreductive supervenient physicalism.).
Suppe, F., (ed.) 1977: The Structure of Scientific Theories . 2nd edn (Urbana, IL: University of Illinois Press ). (Suppe's extended introduction is, among other things, an excellent survey of classical reductive physicalism and its problems.).

WILLIAM SEAGER

A Companion to the Philosophy of Science