The spectrum of materialisms

By the 1950s a burgeoning physicalist ideology led philosophers to go beyond the methodological scientism of behaviorism and try to develop an explicitly materialist theory of mind. (I prefer the term “physicalist” to “materialist,” but in this part of the literature the term “materialist” is almost always used so I will follow popular usage.) This movement had everything to do with the intense flowering of technology in this period. For example, electrodes fine enough to penetrate neural axons without destroying them allowed for the measurement and tracking of electrochemical events in live brains. This immediately led to demonstrations of correlations between specific areas of the brain and specific mental abilities and processes. It seemed to be common sense that the materialist program would essentially consist of identifying mental states with physical states (of the brain): “identity theory.”

This is reductive materialism, the view that the descriptive and explanatory language of psychology can be reduced (or translated, or analyzed) into the language of neurophysiology (or maybe just physiology: the argument here does not depend on anyone holding that the brain is the only part of the body that instantiates mental states, although many have held that position. I will continue to use the word “brain” for the sake of exposition). The identity theorists couldn’t say that brain states caused mental states or somehow underlay mental states because that would still distinguish the mental from the physical. The theory had to say that what mental states really were were physical states. Reductive materialism/identity theory is common sense (albeit incorrect) materialism, and stands at the center of the materialist spectrum, with a wing on either side (I have heard philosophers refer to the two wings as the “right wing” and the “left wing,” but I neither understand that categorization nor see how it is useful. One can make arguments to the effect that either wing is the “right” or the “left” one).

The essential metaphysical problem for reductive materialism is not, in retrospect, hard to see: intentional states are multiply realizable, supervenient on their physical exemplars. (A crucial point for the larger argument of this book is that this is a problem for intentional states specifically; the following arguments do not go through for consciousness.) Since the extension of the set of potential subjects of intentional predicates is not fixable with any physical specifications, reductive materialism is “chauvinistic,” as it means to identify a given intentional state (the belief that there are fish in the barrel, say) with some specific human brain state.

Functionalism is a response to this metaphysical problem. Functionalism stresses the type/token distinction: while token-to-token identity is possible, type-to-type identity is not. That is, every token (every actual instance) of an intentional state is instantiated by some specific physical state (assuming physicalism, which technically speaking functionalism doesn’t have to do). Functionalism plus physicalism is non-reductive materialism, one of the wings of the materialist spectrum. Functionalism abstracts away from the token physical instantiations by replacing physical descriptions with functional descriptions. (Aristotle, trying to block the reductive materialism of Democritus, located this block at the level of biological description rather than psychological description, and his ideas continue to be of the utmost importance for philosophy of mind to this day.) A mature functionalist psychology, free of references to the human body, would amount to a generic set of performance specifications for an intelligent being; in this way functionalism (that is cognitive psychology, computer science, logic, robotics and other functional-descriptive pursuits) provides a “top-down” model for backwards-engineering the human nervous system itself, tunneling towards a link with the “bottom-up” (or “wetware”) researches of neurophysiology, evolutionary biology, physical anthropology etc.

Although functionalism is of great use as a heuristic it is not clear that non-reductive materialism, considered as a theory of mind, succeeds in addressing the problem of mental representation, let alone in resolving it. On the non-reductive materialist theory a given mental state, for example the belief that the fish are in the barrel, is defined as any physical state X that plays the appropriate causal role in the production of behavior, as in “Flipper is trying to upend the barrel because Flipper desires fish and X.” This formula usefully allows for the possibility that the relevant function might be achieved without the use of representations, but it doesn’t rule out the use (the existence) of representations. In failing to resolve the problem of the semantic property (or, for that matter, the problem of rationality) in favor of a physicalist semantic functionalism is something less than a full-blown “theory of mind.”

However, functionalism, or I should say the recognition of the problem of multiple realizability that motivates functionalism, does express the central problem for the other wing of the materialist spectrum. On the other side of reductive materialism from non-reductive materialism is eliminative materialism. Eliminative materialism emphasizes the possibility that a mature naturalized psychology need not be expected to provide a physical semantic of intentional states. The eliminativist argues that it is possible that the intentional vocabulary might instead be replaced altogether with a new, physical vocabulary. After all, while Zeus’s thunderbolts have been inter-theoretically reduced to electrical discharges, the heavenly spheres are not identified with anything in our contemporary astronomy. The history of science provides many examples of both reduction and elimination. The research program of cognitive science cannot just assume that the categories of traditional intentional psychology (“folk psychology”) carve the psychological world at its joints. Thus eliminativists propose the “Theory Theory,” the idea that the intentional vocabulary amounts to a particular theory about the mind, and that it is an old vocabulary that might be eliminated rather than reduced.

My uncle Ed, a devotee of corny jokes, likes to tell the one about the tourist who pulls over to ask the local how to get to Hoboken (all of Ed’s jokes are set in his beloved New Jersey). Thinking it over, the local finally says, “You can’t get there from here.” Eliminativism about the intentional vocabulary has a you-can’t-get-there-from-here problem. To say that the intentional vocabulary is subject to elimination is to say that we might talk another way. But as things stand, it can only be said of the eliminativist that they desire to show that we need not necessarily speak of desires, that they believe that “beliefs” are part of an eliminable vocabulary, and so on. For a time I thought that this merely indicated that eliminativism, like functionalism, was something less than a fully realized theory of mind, but the problem is more serious than that and we can see why by considering once again the problem of multiple realizability.

Socrates asks the young men to define justice. They try to explain the property by giving examples of just and unjust actions and of situations where justice does or does not obtain. Socrates rejects this method: examples of justice, he argues, can never be the definition of justice. Plato thinks that supervenient properties are transcendental properties. They do not emerge, somehow, from the contingent physical world (like Aristotle Plato is opposed to reductive materialism). Rather the physical world takes on intelligible form through participation, somehow, with the transcendental (I will return to Plato’s metaphysics in the discussion of the problem of rationality below). The supervenient nature of these properties demonstrates, to Plato’s mind, that they do not come to be and pass away along with their various, impermanent, physical instantiations. Plato was the first philosopher to recognize that intentional predicates supervene on multiple physical things; ultimately his argument is that souls are immortal because properties are immortal.

“Or again, if he (Anaxagoras) tried to account in the same way for my conversing with you, adducing causes such as sound and air and hearing and a thousand others, and never troubled to mention the real reasons, which are that since Athens has thought it better to condemn me, therefore I for my part have thought it better to sit here…these sinews and bones would have been in the neighborhood of Megara or Boeotia long ago” (Phaedo 98d).

Wittgenstein rejected Plato’s search for transcendent essences, but not the ineliminable nature of the intentional predicates. While Wittgenstein thinks that individual, concrete instances of uses of a word (that is, the set of actual tokens of the word) are all there is to the “meaning” of the word (“meaning” is simply use), he identifies psychological predicates with a form of life: “To imagine a language is to imagine a life-form.” Like Aristotle Wittgenstein identifies psyche with life itself, not with the “mind” (towards which he has a Humean skepticism).

In sum, what the multiple-realizability (the supervenient nature) of intentional predicates demonstrates is that they cannot be replaced with some other way of talking. We can no more dispense with “belief” or “desire” than we can with “beauty” or “justice.” These words simply do not refer to any finite, specifiable set of physical characteristics of any finite, specifiable set of physical things. At a minimum this strongly suggests that the intentional vocabulary is ineliminable. (Again, none of this holds for phenomenal predicates. They require a completely different treatment that they will get in Chapter Three.) It follows from this that intentional predicates do not refer to any “internal” states at all, which is the key to developing a natural semantic for them.

First, though, let’s finish the discussion of eliminative materialism. There are two types of eliminativism. The first is the kind I have been discussing, the kind usually associated with the name: eliminativism about intentional predicates. But we have seen that physical analysis of nervous systems has no greater prospect of eliminating intentional predicates than physical analysis of works of art does of eliminating aesthetic predicates. What physicalism does both promise and require is the elimination of any reference to clearly non-physical properties (supervenient properties are not “clearly non-physical”; what their metaphysical status is continues to be the question that we are asking).

No, the clearly non-physical property in which intentional predication allegedly involves us has been clear all along: the semantic property. The only eliminativism worthy of that mouthful of a name is content eliminativism. As Jerry Fodor has written, “I suppose that sooner or later the physicists will complete the catalogue they’ve been compiling of the ultimate and irreducible properties of things. When they do, the likes of spin, charm, and charge will perhaps appear on their list. But aboutness surely won’t; intentionality simply doesn’t go that deep.” Representation is the only game that we know is not in town (although some further discussion of Fodor, one of the most important contemporary writers on this topic and a champion of the representational theory, will be necessary below). How ironic, then, that some of the philosophers most closely associated with “eliminative materialism” are in fact very much wedded to the representational paradigm when mental representation is the one and only thing that physicalism has to eliminate in order to be physicalism at all.