Eliminative Materialism and the Propositional Attitudes

Staying within an objectual interpretation of the quantifiers, perhaps the simplest way to make systematic sense of expressions like ' x believes that P ' and closed sentences formed therefrom is just to construe whatever occurs in :he nested positior. held by 'p', 'g', etc. as there having the function of a singular term. Accordingly, the standard connectives, as they occur between terms in that nested position, must be construed as there functioning as operators that form cornpound singular terms from other singular terms, and not as sentence operators. The compound singular terms so formed denote the appropriate compound propositions. S~lbstitutional quantification will of course underwrite a different interpretation, and there are other approaches as well. Especially appealing is the prosentential approach of Dorothy Grover, Joseph Camp, and Nuel Belnap, "A Prosentential 'Theory of Truth," Philosophical Studies, s x v ~ r , 2 (February 1975): 73-125. But the resolution of these issues is not \ ital to the present discussion. 72 THE JOURNAL OF PHILOSOPHY Finally, the realization that folk psychology is a theory puts a new light on the mind-body problem. The issue becomes a matter of how the ontology of one theory (folk psychology) is, or is not, going to be related to the ontology of another theory (completed neuroscience) ; and the major philosophical positions on the mindbody problem emerge as so many different anticipations of what future research will reveal about the intertheoretic status and integrity of folk psychology. The identity theorist optimistically expects that folk psychology will be smoothly reduced by'completed neuroscience, and its ontology preserved by dint of transtheoretic identities. The dualist expects that it will prove irreducible to completed neuroscience, by dint of being a nonredundant description of an autonomous, nonphysical domain of natural phenomena. The functionalist also expects that it will prove irreducible, but on the quite different grounds that the internal economy characterized by folk psychology is not, in the last analysis, a law-governed economy of natural states, but an abstract organization of functional states, an organization instantiable in a variety of quite different material substrates. I t is therefore irreducible to the principles peculiar to any of them. Finally, the eliminative materialist is also pessimistic about the prospects for reduction, but his reason is that folk psychology is a radically inadequate account of our internal activities, too confused and too defective to win survival through intertheoretic reduction. On his view it will simply be displaced by a better theory of those activities. Which of these fates is the real destiny of folk psychology, we shall attempt to divine presently. For now, the point to keep in mind is that we shall be exploring the fate of a theory, a systematic, corrigible, speculative theory. Given that folk psychology is an empirical theory, i t is a t least an abstract possibility that its principles are radically false and that its ontology is an illusion. With the exception of eliminative materialism, however, none of the major positions takes this possibility seriously. None of them doubts the basic integrity or truth of folk psychology (hereafter, "FP"), and all of them anticipate a future in which its laws and categories are conserved. This conservatism is not without some foundation. After all, F P does enjoy a substantial amount of explanatory and predictive E:LIMINATIVE MATERIALlSM 73 success. And what better grounds than this for confidence in the integrity of its categories ? LThat better grounds indeed? Even so, the presumption in FP's favor is spurious, born of innocence and tunnel vision. A more searching examination reveals a different picture. First, we must reckon not only with FP's successes, but with its explanatory failures, and with their extent and seriousness. Second, we must consider the long-term history of FP, its growth, fertility, and current promise of future development. And third, we must consider what sorts of theories are likely to be true of the etiology of our behavior, given what else we have learned about ourselves in recent history. That is, we must evaluate F P with regard to its coherence and continuity with fertile and well-established theories in adjacent and overlapping domains-with evolutionary theory, biology, and neuroscience, for example-because active coherence with the rest of what we presume to know is perhaps the final measure of any hypothesis. A serious inventory of this sort reveals a very troubled situation, one which would evoke open skepticism in the case of any theory less familiar and dear to us. Let me sketch some relevant detail. When one centers one's attention not on what F P can explain, but on what it cannot explain or fails even to address, one discovers that there is a very great deal. As examples of central and important mental phenomena that remain largely or wholly mysterious within the framework of FP, consider the nature and dynamics of mental illness, the faculty of creative imagination, or the ground of intelligence differences between individuals. Consider our utter ignorance of the nature and psychological functions of sleep, that curious state in which a third of one's life is spent. Reflect on the common ability to catch an outfield fly ball on the run, or hit a moving car with a snowball. Consider the internal construction of a 3-D visual image from subtle differences in the 2-D array of stimulations in our respective retinas. Consider the rich variety of perceptual illusions, visual and otherwise. Or consider the miracle of memory, with its lightning capacity for relevant retrieval. On these and many other mental phenomena, F P sheds negligible light. One particularly outstanding mystery is the nature of the learning process itself, especially where i t involves large-scale conceptual change, and especially as it appears in its pre-linguistic or entirely nonlinguistic form (as in infants and animals), which is by far the most common form in nature. F P is faced with special 7 1 THE JOURNAL OF PHILOSOPHY difficulties here, since its conception of learning as the manipulation and storage of propositional attitudes founders on the fact that how to formulate, manipulate, and store a rich fabric of propositional attitudes is itself something that is learned, and is only one among many acquired cognitive skills. F P would thus appear constitutionally incapable of even addressing this most basic of mysteries4 Failures on such a large scale do not (yet) show that F P is a false theory, but they do move that prospect well into the range of real possibility, and they do show decisively that F P is at best a highly superficial theory, a partial and unpenetrating gloss on a deeper and more complex reality. Having reached this opinion, we may be forgiven for exploring the possibility that F P provides a positively misleading sketch of our internal kinematics and dynamics, one whose success is owed more to selective application and forced interpretation on our part than to genuine theoretical insight on FP's part. A look a t the history of F P does little to allay such fears, once raised. The story is one of retreat, infertility, and decadence. The presumed domain of F P used to be much larger than it is now. In primitive cultures, the behavior of most of the elements of nature were understood in intentional terms. The wind could know anger, the moon jealousy, the river generosity, the sea fury, and so forth. These were not metaphors. Sacrifices were made and auguries undertaken to placate or divine the changing passions of the gods. Despite its sterility, this animistic approach to nature has dominated our history, and it is only in the last two or three thousand years that we have restricted FP's literal application to the domain of the higher animals. Even in this preferred domain, however, both the content and the success of F P have not advanced sensibly in two or three thousand years. The F P of the Greeks is essentially the F P we use today, and we are negligibly better a t explaining human behavior in its terms than was Sophocles. This is a very long period of stagnation and infertility for any theory to display, especially when faced with such an enormous backlog of anomalies and A possible response here is t o insist that the cognitive activity of animals and infants is linguaformal in its elements, structures, and processing right from birth. J. A. Fodor, in The Language of Thought (New York: Crowell 1975), has erected a positive theory of thought on the assumption that the innate forms of cognitive activity have precisely the for111 here denied. For a critique of Fodor's view, see Patricia Churchland, "Fodor on Language Learning," .Yynthese, X X X ~ I I I ,1 (hlay 1978): 149-159. ELIMINATIVE MATERIALISM 75 mysteries in its own explanatory domain. Perfect theories, perhaps, have no need to evolve. But F P is profoundly imperfect. Its failure to develop its resources and extend its range of success is therefore darkly curious, and one must query the integrity of its basic categories. To use Imre Lakatos' terms, F P is a stagnant or degenerating research program, and has been for millennia. Explanatory success to date is of course not the only dimension in which a theory can display virtue or promise. A troubled or stagnant theory may merit patience and solicitude on other grounds; for example, on grounds that it is the only theory or theoretical approach that fits well with other theories about adjacent subject matters, or the only one that promises to reduce to or be explained by some established background theory whose domain encompasses the domain of the theory a t issue. In sum, it may rate credence because it holds promise of theoretical integration. How does F P rate in this dimension ? I t is just here, perhaps, that F P fares poorest of all. If we approach homo sapiens from the perspective of natural history and the physical sciences, we can tell a coherent story of his constitution, development, and behavioral capacities which encompasses particle physics, atomic and molecular theory, organic chemistry, evolutionary theory, biology, physiology, and materialistic neuroscience. That story, though still radically incomplete, is already extremely powerful, outperforming F P a t many points even in its own domain. And it is deliberately and self-consciously coherent with the rest of our developing world picture. In short, the greatest theoretical synthesis in the history of the human race is currently in our hands, and parts of it already provide searching descriptions and explanations of human sensory input, neural activity, and motor control. But F P is no part of this growing synthesis. Its intentional categories stand magnificently alone, without visible prospect of reduction to that larger corpus. A successful reduction cannot be ruled out, in my view, but FP's explanatory impotence and long stagnation inspire little faith that its categories will find themselves neatly reflected in the framework of neuroscience. On the contrary, one is reminded of how alchemy must have looked as elemental chemistry was taking form, how Aristotelean cosmology must have looked as classical mechanics was being articulated, or how the vitalist conception of life must have looked as organic chemistry marched forward. 76 THE JOURNAL OF PHILOSOPHY In sketching a fair summary of this situation, we must make a special effort to abstract from the fact tha t F P is a central part of our current lebenszlelt, and serves as the principal vehicle of our interpersonal commerce. For these facts provide FP with a conceptual inertia tha t goes far beyond its purely theoretical virtues. Restricting ourselves to this latter dimension, what we must say is that F P suffers explanatory failures on an epic scale, tha t i t has been stagnant for a t least twenty-five centuries, and tha t its categories appear (so far) to be incommensurable with or orthogonal to the categories of the background physical science whose long-term claim to explain human behavior seems undeniable. Any theory tha t meets this description must be allowed a serious candidate for outright elimination. \\ie can of course insist on no stronger conclusion a t this stage. Nor is it my concern to do so. \\ie are here exploring a possibility, and the facts demand no more, and no less, than i t be taken seriously. The distinguishing feature of the eliminative materialist is that he takes it very seriously indeed. 111. ARGUMENTS AGAINST ELIRIINATION Thus the basic rationale of eliminative materialism : F P is a theory, and quite probably a false one; let us a t tempt , therefore to transcend it. The rationale is clear and simple, but many find i t uncompelling. I t will be objected tha t F P is not, strictly speaking, an empir ical theory; tha t it is not false, or a t least not refutable by empirical considerations; and tha t i t ought not or cannot be transcended in the fashion of a defunct empirical theory. In what follows we shall examine these objections as they flow from the most popular and best-founded of the competing positions in the philosophy of mind : functionalism. An antipathy toward eliminative materialism arises from two distinct threads running through contemporary functionalism. The first thread concerns the normative character of F P , or a t least of tha t central core of F P which treats of the propositional att itudes. F P , some will say, is a characterization of an ideal, or a t least praiseworthy mode of internal activity. I t outlines not only what i t is to have and process beliefs and desires, but also (and inevitably) what i t is to be rational in their administration. T h e ideal laid down by F P may be imperfectly achieved by empirical humans, but this does not impugn F P as a normative characterization. Nor need such failures seriously impugn F P even as a descriptive characterization, for i t remains true tha t our activiELIMINATIVE MATERlALlSM 7 7 ties can be both usefully and accurately understood as rational except for the occasional lapse due to noise, interference, or other breakdown, which defects empirical research may eventually unravel. Accordingly, though neuroscience may usefully augment i t , F P has no pressing need to be displaced, even as a descriptive theory; nor could i t be replaced, qua normative characterization, by any descriptive theory of neural mechanisms, since rationality is defined over propositional attitudes like beliefs and desires. F P , therefore, is here to stay. Daniel Dennett has defended a view along these l ines6 And the view just outlined gives voice to a theme of the property dualists as well. Karl Popper and Joseph Margolis both cite the normative nature of mental and linguistic activity as a bar to their penetration or elimination by any descriptive/materialist t h e ~ r y . ~ I hope to deflate the appeal of such moves below. The second thread concerns the abstract nature of FP. The central claim of functionalism is tha t the principles of F P characterize our internal states in a fashion tha t makes no reference to their intrinsic nature or physical constitution. Rather, they are characterized in terms of the network of causal relations they bear to one another, and to sensory circumstances and overt behavior. Given its abstract specification, that internal economy may therefore be realized in a nomically heterogeneous variety of physical systems. All of them may differ, even radically, in their physical constitution, and yet a t another level, they will all share the same nature. This view, says Fodor, "is compatible with very strong claims about the ineliminability of mental language from behavioral theories." Given the real possibility of multiple instantiations in heterogeneous physical substrates, we cannot eliminate the functional characterization in favor of any theory peculiar to one such substrate. T h a t would preclude our being able to describe the (abstract) organization tha t any one instantiation shares with all the other. A functional characterization of our internal states is therefore here to stay. This second theme, like the first, assigns a faintly stipulative character to F P , as if the onus were on the empirical systems to 5 Most explicitly in "Three Kinds of Intentional Psychology" (forthcoming), but this theme of Dennett's goes all the way back to his "Intentional Systems," this JOURNAL, LXVIII, 4 (Feb. 25, 1971): 87-106; reprinted in his Brainstorms (Montgomery, Vt.: Bradford Books, 1978). Popper, Objectiale Knowledge (New York: Oxford, 1972); with J. Eccles, The Self and Its Brain (New York: Springer Verlag, 1978). Margolis, Persons and Minds (Boston : Reidel, 1978). 7 Psychological Explanation (New York: Random House, 1968), p. 116. 78 THE JOURNAL OF PHILOSOPHY instantiate faithfully the organization tha t F P specifies, instead of the onus being on F P to describe faithfully the internal activities of a naturally distinct class of empirical systems. This impression is enhanced by the standard examples used to illustrate the claims of functionalism-mousetraps, valve-lifters, arithmetical calculators, computers, robots, and the like. These are artifacts, constructed to fill a preconceived bill. In such cases, a failure of fit between the physical system and the relevant functional characterization impugns only the former, not the latter. T h e functional characterization is thus removed from empirical criticism in a way tha t is most unlike the case of an empirical theory. One prominent functionalist-Hilary Putnam-has argued outright tha t F P is not a corrigible theory a t a l l . V l a i n l y , if F P is construed on these models, a s regularly i t is, the question of its empirical integrity is unlikely ever to pose itself, let alone receive a critical answer. Although fair to some functionalists, the preceding is not entirely fair to Fodor. On his view the aim of psychology is to find the best functional characterization of ourselves, and what that is remains an empirical question. As well, his argument for the ineliminability of mental vocabulary from psychology does not pick ou t current F P in particular a s ineliminable. I t need claim only tha t some abstract functional characterization must be retained, some articulation or refinement of E'P perhaps. His estimate of eliminative materialism remains low, however. First, i t is plain tha t Fodor thinks there is nothing fundamentally or interestingly wrong with FP . On the contrary, FP 's central conception of cognitive activity-as consisting in the manipulation of propositional attitudes-turns up as the central element in Fodor's own theory on the nature of thought ( T h e Language of Thought, op. cit.). And second, there remains the point tha t , whatever tidying up F P may or may not require, i t cannot be displaced by any naturalistic theory of our physical substrate, since i t is the abstract functional features of his internal states tha t make a person, not the chemistry of his substrate. All of this is appealing. But almost none of i t , I think, is right. Functionalism has too long enjoyed its reputation a s a daring and avant garde position. I t needs to be revealed for the short-sighted and reactionary position i t is. IV. T H E CONSERVATIVE NATURE O F FUNCTIONALISM A valuable perspective on functionalism can be gained from the following story. T o begin with, recall the alchemists' theory of "Robots: Machines or Artificially Created Life?", this J O U R K A L , LXI , 21 (Nov. 12, 1961): 668-691, pp. 675, 681 ff. 79 ELlMlNATIVE MATERIALISM inanimate matter. \Ye have here a long and variegated tradition, of course, not a single theory, but our purposes will be served by a gloss. The alchemists conceived the "inanimate" as entirely continuous with animated matter, in that the sensible and behavioral properties of the various substances are owed to the ensoulment of baser matter by various spirits or essences. These nonmaterial aspects were held to undergo development, just as we find growth and development in the various souls of plants, animals, and humans. The alchemist's peculiar skill lay in knowing how to seed, nourish, and bring to maturity the desired spirits enmattered in the appropriate combinations. On one orthodoxy, the four fundamental spirits (for "inanimate" matter) were named "mercury," "sulphur," "yellow arsenic," and "sal ammoniac." Each of these spirits was held responsible for a rough but characteristic syndrome of sensible, combinatorial, and causal properties. The spirit mercury, for example, was held responsible for certain features typical of metallic substancestheir shininess, liquefiability, and so forth. Sulphur was held responsible for certain residual features typical of metals, and for those displayed by the ores from which running metal could be distilled. Any given metallic substarice was a critical orchestration principally of these two spirits. A similar story held for the other two spirits, and among the four of them a certain domain of physical features and transformations was rendered intelligible