Materialism and the Two Existential Questions

It is hard to see the import of a metaphysical argument that has no epistemological implications. If dualism about body and mind is correct an interaction problem will have to be dealt with. By the same token if materialism is to be taken seriously it will have to provide a naturalized account of causal explanation. I take this to mean that to espouse materialism is to commit oneself to the view that a “closed” physical explanation, that is an explanation that refers only to physical causes, is possible. Many materialists understand this to mean that there can only be one “existential question,” if an existential question is one that might not have an answer: “Why is there something rather than nothing?” The idea is that there must be absolutely nothing inherently organized about the something that exists, because materialism is the bare claim that only matter exists and must accomplish everything starting from that sole axiom. Remember, too, that early modern materialism was closely linked with empiricism, forged in opposition to the classical tradition of Neo-Platonism, Christianity and rationalist philosophy and programmatically hostile to metaphysics.

Consider, for example, the argument traditionally called “the teleological proof for the existence of God” or more recently “the intelligent design argument.” Put in currently popular terms, the argument is that the complex design of the natural universe is evidence for an intelligent designer. In this context there is a significant difference between this sort of view and double-aspect theories that see mind and matter as one ontological being, under two kinds of description. (In addition to Spinoza many Hindi and Buddhist philosophers develop versions of double-aspect theory.) In so far as the design argument is an argument meant to demonstrate the existence of another being, the intelligent agent nominally responsible for the design of nature, the argument fails. The design argument starts by asserting that any finely-organized entity must have some sort of explanation. In the case of the natural world, an evidently finely-organized entity, the explanation offered is that there exists an intelligent designer. But the advocate of the intelligent design argument, in so far as he or she takes the argument to show that an intelligent designer ontologically distinct from the natural world exists, now looks committed to the need for an explanation of this finely-organized entity in turn.

To read this back into theory of mind, a materialist theory of mind has to get to mind from no-mind. The intelligent design argument fails because it is intelligence itself (in Platonic terms, the intelligibility of the universe) that we are trying to explain, and pushing the problem back a step is a failure to explain, just as saying that representations are interpreted in your head fails to explain how you, an actual person out in the world, actually interprets anything.

However, it may be that some materialists have over-reacted to the danger posed by the slippery slope that supposedly leads from recognizing that the physical universe may have some innate organization to…what? Say, full-blown Roman Catholicism? Perhaps it is simply a matter of two existential questions, not one. In addition to “Why is there something rather than nothing?” maybe “Why is the something that there is organized such that complex physical systems with formal properties arise?” To come to accept that the universe is a formally organized place can be an entirely secular resolution, after all. Materialist biologists arguing against creationism in the public schools don’t want to work themselves into an even weirder position than that of their religiously-motivated, intelligent design-espousing opponents.

The question then becomes, does accepting that there are two existential questions, not one, entail conceding that materialism is false? I think that in a way it does. If it makes sense to say that formal organization a) exists (“obtains”: I take the Aristotelean view that formal organization, if it is real, is a feature of the physical universe) and b) is a further, contingent fact (that is, there could have been a physical universe that was not formally organized to any degree) then materialism in its most orthodox version is false. I will go so far as to say that this appears to me to be the most plausible resolution to the problem of rationality, and that I do not think that it would be the end of the world if materialism were modified in this way. It is often pointed out that contemporary physics’ picture of “matter/energy” is now so strange that the concept of “materialism” probably can’t do much reliable reductive work anyway. And it is striking that physics has become more and more mathematical as the modern movement of physics has progressed over the passed one hundred years or so.

I think, though, that I can have my resolution to the problem of rationality without settling the cosmological question about the existence (or lack thereof) of innate universal order. The orthodox materialist might be able to explain how complex, self-replicating forms emerged from random, chaotic interactions, such that there is no need for “innate order.” Or materialism may fail to do this. It is enough for my thesis if formal properties are ubiquitous in worlds where rational beings evolve. How those worlds got that way is irrelevant to the point, which is that rationality is (just) another formal property and, although rational beings may be breathtaking examples of finely-formed entities, they are not therefore ontologically distinct from the rest of the physical universe.

Plato and the Metaphysical Problem of Rationality

Plato, like Kant, was reacting to contemporary currents of thought that he regarded as dangerous. He took seriously an epistemological problem that he thought was posed by Heraclitus’ doctrine of universal flux (Plato disregards Heraclitus’ view that “all things happen in accord with the divine Logos” and sets Heraclitus up as the materialist foil to Parmenides). In a world where nothing was eternal, unchanging and universal, knowledge with those qualities was also not possible: it had no object. To try to compose a description of an ever-fluxing world was like “shooting after flying game” (as Socrates says in the Theatetus). That sort of knowledge was a snapshot of a mere moment, quickly passed. Plato’s strategy for addressing this epistemological problem was metaphysical: identify the eternal, unchanging and universal object.

Plato also opposed the reductive materialism of Anaxagoras and the other Melisians, early natural scientists (Aristotle, who shared Plato’s opposition to reductive materialism, addresses Democritus’ atomism). The word “reductive” in the phrase “reductive materialism” is also epistemological in its import: the idea is that macro-level phenomena (such as the minds of persons) will ultimately be explained in terms of micro-level phenomena (such as the parts of bodies). Materialism understood this way is committed to the view that properties are caused by matter. The materialist answer to the question “Why is this property what it is?” is “Because the underlying matter is what it is.” Both Plato and Aristotle argued that causation (and thus explanation) ran the other way.

Plato and Aristotle hold respective versions of the form-matter distinction, the view that basic ontology includes both form and matter. Plato’s version is patently dualist. He holds that form is primary being, that it is mind- and matter-independent, and that formal being acts on material being such that matter can only be said to be something to the degree that it is involved in form. Aristotle, objecting to what he saw as Plato’s ontological promiscuity, argued that substance, a union of matter and form, was primary being. Among other advantages this resolved the interaction problem that afflicts Plato’s dualism. On the other hand, the price of collapsing matter and form together into substance in this axiomatic way was that one had to accept that primary being was heterogeneous. This is counter-intuitive, but that doesn’t make it wrong. Close attention to Aristotle’s metaphysical differences with Plato is rewarded with any number of insights into subtleties of the mind-body problem (for example notice the resonance with Spinoza). We will return to Aristotle and De Anima, his own great work on the philosophy of mind, in Chapter Four.

However I will argue that these differences, significant as they are, are not relevant to the present, relatively broad point I want to make about the form-matter distinction, materialism, and the problem of rationality. Ultimately I’m more of an Aristotelian than a Platonist, but I think Plato’s more explicitly dualist discussion makes this broad point best so I will discuss two passages from Plato, the “analogy of the sun” at Republic 507b-509c and the treatment of the materialist argument that “soul is an attunement of the body” at Phaedo 93a-94e.

The Sun, Plato says, makes the universe a visible place. Our eyes take advantage of this (Plato and Aristotle resisted Empedocles’ arguments for natural selection, which they saw as reductive, but the reader should join me in helping ourselves to evolutionary biology wherever it helps to fill things in here). We can see each individual visible thing because the whole universe is suffused with that one element, light, which emanates from the Sun. Analogously Plato claimed that something he called “the Good” suffused the universe with order and made it an intelligible place. The Sun is to vision as the Good is to rationality: both vision and rationality are possible because of the existence of a more general feature of the universe. Plato takes the analogy farther. The Sun’s light is necessary for the growth of plants and the Good’s order is necessary for the emergence of definite (definable, intelligible) things. The Sun is the source of warmth; the Good is the source of value. Darkness is the absence of light; badness is the absence of order.

Describe any concrete particular thing. You will describe it (you can only describe it) in terms of its properties. Concrete particulars, as Heraclitus pointed out, are constantly coming-to-be and passing away. Properties (forms, universals) are eternal. The epistemological challenge posed by Heraclitus’ doctrine of universal flux is met with the Platonic doctrine that formal knowledge (knowledge of formal properties), as distinct from material knowledge (knowledge of concrete particulars), constitutes true understanding.

However there are properties and then there are properties. I stated at the beginning of the book that I don’t like a lot of loose talk about “properties” and that ultimately I think that physical properties are the only kind of properties that there are. If I am going to qualify that at all (and at the end of this discussion you will be left with your own judgment to decide how far I have gone in that direction, and if too far), then I had better try to be a good deal more precise about what I mean by “formal properties.”

Consider two putative properties: the property of “cowness” (or “being-a-cow” or what you will) and the property of circularity. According to Plato, as matter approaches nearer to form it comes to be something, “being” meaning “being intelligible,” which to Plato is a legitimate ontological category (Plato posits degrees of being, contrary to the materialist’s zero-sum understanding of being). However, while there are certainly well-formed cows and malformed cows, even a cow still-born with deformity is a cow (if someone comes into the barn and asks, “What is that?” the right answer is “That’s a cow.”). Plato and Aristotle thought that species were fixed natural kinds (to use the standard phrase), but we (well, I) don’t think so: species are the kinds of things that come-to-be and pass away, just as individuals do. With circularity the situation is different. Being a circle just is having (instantiating) that property, and there is a threshold of trueness short of which we will say that the concrete particular isn’t a circle in a sense that it cannot be said, of any animal born of cows, that it “isn’t a cow.” Once a cow, always a cow, but a concrete particular can gain and lose the property of circularity.

The extension of the set of all formal properties can only be understood in the context of Plato’s central metaphysical thesis of the Good. Plato is clear on the difference between material being and formal being. Material being is divisible (Socrates’ body can be chopped up into pieces and scattered like leaves or burnt and blown away like smoke), it is a multiplicity (I am one body, you are another), and it comes-to-be and passes away (“All men are mortal, Socrates is a man…”). What part of reality is indivisible, a unity (oneness), and eternal?

Imagine (if this is the sort of thing that can be imagined) that one’s sole mathematical practice was to name one set, {x,x}, let’s call it “2.” Now we reflect on our named set and it occurs to us that we need a name for the constituent set, {x}, so we call it something: “1.” It is now impossible not to notice a pair of functions, “+” and “=.” From these we will inevitably get to the other functions, and we also now have a practice of naming all sets; we have the set of natural numbers. In fact all of mathematics is entailed by any part of mathematics. Mathematics cannot be cut into pieces. To have it is to have, at least implicitly, all of it, including all of those proofs that no human has as yet discovered (it is mind-independent). Nor can any part of mathematics be considered, as physical objects can, in isolation from the rest. I can imagine a universe consisting only of this desk chair floating in the vast emptiness of space (I think), but if the proof of the infinity of prime numbers is floating out there, so is all the rest of mathematics. It is one, not a multiplicity of separable propositions. Not only that, but it looks like it is floating out there, since we discover the entailments. And those proofs would be valid, undoubtedly, whether or not there was any matter and energy at all. Mathematics is indivisible, a unity and eternal.

At this point it is possible to be more specific about what a “formal property” is. I take formal properties to be mathematical properties, essentially. For what it’s worth, I even think that this may not be far from Plato’s actual theory, reflecting as it does the metaphysical influence of Pythagoras and Parmenides. To say that a thing has a formal property is to say that there is an aspect or part of that thing that can only be described in terms of mathematical or logical relationships that can be formalized without reference to the contingent physical properties of the thing. For example the property of circularity is a formal property. The set of circular things includes wooden things, clay things, bone things and metal things, but circularity is supervenient: its mathematical description is about the spatial relationship between one of its parts and another and this formalizable (mathematical) relationship does not “reduce” to any contingent properties of wood cells or clay particles etc. That is, “formal properties” are properties that can be formalized. All formal properties are supervenient on matter: there is no physical criterion that fixes the extension of the set of physical things that instantiate the property.

Another way of saying the same thing is to say that any physical object might potentially be involved in any formal property. Formal properties are universal (sometimes they are called “universals”). A critical point here is that strictly speaking there is only one formal property, that property that the universe has of being formally organized by the Good. To speak of a plurality of “forms” (“circularity,” “rationality”) is figurative. There is only one form in which all formally organized things participate; only its expression in matter is multifarious as for example in the various geometrical shapes. (In the next section I will discuss whether and how much this literalist Platonism can coexist with materialism in general and particularly with the Wittgenstein-influenced eliminativism about mental content that I sketched above.)

At Phaedo 93a-94e Socrates is responding to a kind of materialist theory suggested by Simmias. Simmias acknowledges that Socrates can raise difficulties for the identification of the soul with the body by pointing out apparently metaphysical differences between them (for example with the argument from “recollection,” which is Socrates’ term of art for innate knowledge), but Simmias argues that the soul might nonetheless be a kind of “attunement” of the body. This is an emergentist view: when all of the physical properties come together in the right way, a non-physical property emerges, not identical to but dependent on (caused by) the underlying physical properties. Emergentism is a creature of that murky area, populated by refugees and smugglers, where “non-reductive materialism” and “epistemological dualism” share a hopelessly porous border. People who wind up here wanted the goodness of materialism without the badness. Plato’s (dualist) response to the emergentist challenge provides the last link in my argument for a Platonic resolution (I don’t say “solution”) to the problem of rationality.

Consider a musical instrument and the harmonious sounds it makes. On Simmias’ view the harmonious sounds are caused by the particular physical properties of the instrument. Thus while it’s true that the harmony is not identical to the body of the instrument, it is also true that with the passing away of the instrument’s body there will be a simultaneous passing away of the harmony. Socrates responds that harmony is a formal property. That is, harmony itself is not more or less harmonic, any more than circularity is more or less circular. It is physical particulars that can gain or lose circularity, gain or lose harmony. One can get more or less harmonious, but once a lyre always a lyre. The harmony, then, is nothing particular to the lyre; the lyre may have a particular sound in some other aspect, but qua harmonious it participates in the same harmony as every other harmonious object. “Harmonious” is the type, and the extension of the set of physical tokens (musical instruments) cannot be fixed with physical criteria; harmony is formalized in musical notation.

In fact causation runs the other way. Instruments were developed (over a more or less long period of time involving trial and error) according to how well various materials, constructions, forms and so forth achieved harmony. Musical instruments come to be, and are caused to have the physical properties that they have, by virtue of the principles of harmonics. Music is a clear case where the formal property (of harmony) is the antecedent cause of the formation of a set of physical particulars (musical instruments) that exist because they participate in the property. If someone asks, “Why is the lyre shaped like that?” the right answer is, “Because that shape is harmonic.”

Here is the argument towards which I have been working: Consider the three properties circularity, harmony and rationality. They are all formal properties: they are all supervenient and they are all formalizable. The property of rationality is a very fancy formal property compared to circularity, to be sure. But rationality does not constitute, relative to circularity and harmony, any new ontological category. A circular object is an example of an object that possesses both physical and formal properties (in fact both Plato and Aristotle thought that all physical objects possessed formal properties). Meanwhile “immortality of soul” is neither more nor less than “immortality of form.” Remember that ontologically speaking there is only one form: form is a unity, matter a multiplicity. That both a rational human and a circular piece of chalk are involved in the same dualism of form and matter seems difficult to dispute.

Although Plato never, to my knowledge, uses panpsychist language to the effect that non-living objects such as pieces of chalk have souls (a view more explicit in the double-aspect ontology of Spinoza), neither does he say they don’t. Anyway he could be using the word “soul” to refer specifically to rationality and that wouldn’t affect the basic argument here. Socrates comforts his human friends with the argument that humans are constituted out of both matter and rationality, a formal property, and as form is immortal, so that element of humans will never pass away. But obviously a circular object is constituted out of both matter and circularity, and so anything said about a rational object also follows for a circular object as both are understood as possessing a formal property, and the argument turns on the immortality of form.

The result is that what we have been calling “the problem of rationality” turns out to be an instance of a quite general metaphysical problem, the form/matter problem. Now I can discuss the “resolution” to the problem of rationality that this constitutes, but first there are two discussions that are owed to those who have read up to here. The first discussion is about the relationship between the form-matter distinction and materialism: is materialism unable to give a naturalistic account of the formal properties of the universe, including the mind? The second discussion is about whether or not an eliminativist, externalist solution to the problem of representation (such as the one I proposed in the first half of this chapter) can coexist with a Platonic resolution to the problem of rationality.

Plato is not Kant

Kant’s self-styled “Copernican revolution” was a turning inward, to the study of the mind, for solutions to the perennial problems of philosophy. Kant is, among other things, something of a reactionary. Writing at the end of the century of the Enlightenment he sought to defend Christianity, freedom and morality from the threat posed, as he saw it, by empiricism’s atheistic, amoral worldview. Particularly Kant tried to devise an antidote to Hume, and realized that Hume’s Lilliputian psychology, with its denial that anything like the “mind” could even be said to exist beyond the “impressions” caused by sensory experience, was a weak spot in the empiricist argument. Developing an ambitious account of the way the mind organized the “sensory manifold” with a conceptual framework of its own (including the “concepts” of space, time, cause and effect, multiplicity etc), Kant contained the world as understood by the new natural science within a mental representation: the “phenomenal” world was the world as represented by the rational mind, not to be confused with the actual, “noumenal” world.

Kant’s revolution has practically defined philosophy, certainly popular philosophy, ever since. From the German-language transcendental idealists, psychoanalysts, phenomenologists and critical theorists to the French-language existentialists, structuralists and deconstructionists to the English-language phenomenalists, language philosophers and, yes, cognitive scientists, it is hard to find any major philosophical movement of the last two hundred years that does not reflect the influence of Kant. He is one of the few canonical philosophers, whose influence can be seen in the views of the general public, including a great many people who have never heard of him or who do not appreciate that their own views are substantially Kantian. His message that our own minds broadly condition “how we see things” is congenial to a modern world of great cultural, ethnic and political diversity (notwithstanding the fact that Kant himself thought that the rational mind, qua rational, was the same for all).

Although Kant was engaged in a close struggle with Enlightenment empiricism his revolution was not a turning back of the clock. He presented an alternative not only to the empiricists but to the classical metaphysical tradition as well. The eclipse of explicitly metaphysical philosophy for much of the 20th century is of course due to some extent to the cultural impact of modern science, but it also reflects Kant’s core argument that psychological epistemology is first philosophy. What license have we, stuck as we are inside our heads, to make metaphysical speculations about “the external world”?

As a consequence of this it is now difficult for us to appreciate Plato, that most metaphysical of philosophers. So deeply and widely internalized is Kant’s thesis - that the conceptual order of the world is a projection from the mind onto the world - that many people simply cannot hear Plato anymore. In fact many people, even some philosophy professors and certainly a great many students, simply believe that Plato is Kant: the Platonic universals are Kant’s categories. What else could they be, when it is taken as axiomatic that the mind constructs a representation of the world? A smart student, in a typical but relatively explicit exchange, insisted that there was no such thing as the property of circularity or, for that matter, the set of circular concrete particulars: our minds create such categories out of whole cloth, apparently: and this was the view that he ascribed to Plato (he thought that he knew nothing of Kant). He was not at all impressed when I pointed to the two identical circular ceiling fans. Similarity itself, he understood, was a projection of the mind, a feature of the mental representation. As for the textual evidence (which in reality is clear and systematic), Plato is gnostic, all riddles; no one can really understand him. After all, he can’t mean what he is manifestly saying. Attempts to disabuse people of these notions, when not rejected out of hand, are met with bewilderment, anger, and various stages of grief and disillusionment. The slightly more sophisticated perceive that Plato is a bad, bad influence, putting us all at risk of totalitarian dystopia with his irresponsible foundationalism. One of my students told me that her law professor informed the class that he would have voted for Socrates’ execution.

Ah, well. Forgive this old classroom veteran my hobby-horses. Suffice it to say that, for good or ill, Plato is not Kant. Plato is making assertions about the ontology of the universe (of being); just what Kant and his followers claim cannot be done. Listening to what Plato has to say will help us to develop a resolution of the problem of rationality, at least insofar as this problem is one of the mind-body problems. I am not here trying to determine exactly what Plato the individual man actually believed in its fine points. I am not an historian of philosophy. My interest in Plato is the same as my interest in Hilary Putnam or John Searle or Jerry Fodor or for that matter the person sitting next to me on an airplane: if they have interesting ideas that inspire me in my own thinking I am grateful for the acquaintance. The reader whose principal interest is in contemporary philosophy of mind can rest assured that that is my principal interest as well, and that I am not wandering off into exegesis for its own sake. It’s just that I sincerely believe that Plato is the best exemplar of the best argument for resolving the problem of rationality.

Spinoza and Fodor

Spinoza wrote during the transitional 17th century, when the medieval use of the term “God” as a term of art in philosophy overlapped with the early modern interest in the new science, particularly the mechanistic physics that grew out of astronomy and achieved its greatest expression in the work of Isaac Newton at the end of the century. Spinoza took a particular interest in the mind-body problem within the century’s larger preoccupation with reconciling the well-ordered, necessary world revealed by logic and mathematics with the seemingly chaotic, contingent world observed by empirical science. Philosophers of this period are often accused of hiding a thoroughly modern secularism behind religious language so as to avoid trouble with the authorities and to make their modern doctrines go down more easily, but this is a specious interpretation: these thinkers were developing modern ideas out of the old and it was a confusing and difficult process. One has to learn their philosophical language and try to understand their use of the word “God” as a technical term.

Spinoza’s core metaphysical argument is that God can have no limitations: to say that there was anywhere a boundary such that God was on one side and not on the other violated God’s property of universality (notice that one can substitute “mathematics” for “God” here with no loss of sense). Spinoza concludes that the universe (he often uses the term “nature”) is identical to God. It follows that the universe is necessary and perfect. The idea is that the causal processes of nature, seemingly full of contingency and randomness, actually unfold following mathematical necessity (in this regard Spinoza’s views are very close to Newton’s). Humans cannot see this directly due to our own limitations, but we can cultivate an attitude appropriate to the insight.

From this central doctrine Spinoza developed what is commonly called a “double aspect” theory of the relationship between the mind and the body. Everything (the universe) is both the mind and the body of God. Thus everything comes under both a mental and a physical description, which are two ways of looking at the same thing. A benefit of this view is that there is no question about either mental-to-physical or physical-to-mental causation; nor is there any question of choosing between dualism, idealism or materialism: Spinoza presents a monism where the only item of ontology is “God.” Both our mental nature and our physical nature are in fact aspects of our “Godly” (that is, rational) nature. This helps to make sense of the seemingly bizarre doctrine of “synchronicity” developed by Spinoza’s successors Leibniz and Malebranche, which expresses essentially the same idea: the mental and the physical are both explained by a common, antecedent source, which also explains how they are linked (for Spinoza they are one).

Spinoza’s metaphysics leads him to the strikingly modern position of rejecting dualist language about, for example, the mind being the controlling cause of the body’s movements (the ghost in the machine). But also Spinoza rejects the idea that the physical world (the “mode of extension”) is anything random or otherwise contingent. The physical/extended world has structure that corresponds to the mental world. His insight that fine-grained physical processes in the body instantiate the fine-grained processes of the mind (the body is “the object of the mind”) is achieved not by eliminating rationality (as Hume attempts to do) but by merging the rational and the physical.

The contemporary philosopher Jerry Fodor develops a similar line. Fodor understands that physicalism requires that the non-physical property of intentionality be washed out of the ultimate account of things, but he is convinced that mental content is ineliminable: two positions that would appear to be mutually exclusive. What account of mental representation can be given that does not involve us in reference to the semantic property? Fodor proposes to translate semantic properties into syntactic properties. The syntactic structure of the proposition (that is, of the mental representation that is implicit in the intentional attribution) maps on to the computational structure of cognition, which can be cashed out at the machine-language level. A “machine-language” isn’t really a language at all, in the sense of “language” as a symbol-system with semantic content. In the case of computers, binary code (1s and 0s) represents the physical state of the electronic gates in the microchips (open or closed). As the creators of computers we can explain the words and images on the computer screen in terms of the underlying physical process.

Uncovering the machine-language of the nervous system looks like a holy grail for cognitive science. But computers are artifacts that, ultimately, move symbols around for human beings to interpret, so the computer analogy doesn’t go through: actual mental content of the sort that (as Searle demonstrates, convincingly to my mind, with the Chinese Room) computers utterly lack has to be explained without appeal to an interpreter. The mental must be explained wholly in non-mental terms. Computers have the mental already built in: their human users. Fodor’s most expensive proposal is his idea that the causal role of mental content can be explained wholly in terms of the syntactical properties of the representation: that syntax alone can perform the function of sustaining and respecting the logical entailments between the propositions. This requires that he rejects meaning holism in favor of meaning atomism: like immune system antibodies, each mental concept must be latent and autonomous. This is also necessary if we are to keep cognitive psychology (as Fodor believes we must) “in the head.”

I have already expressed my sympathies for externalism and my eliminativism regarding mental representation. However I come not to bury Fodor but to praise him. Fodor has the same insight as Spinoza: to understand the identity of the mental and the physical requires that we understand not only the mental as, in some sense, physical but also the physical as, in some sense, mental. The problem of rationality, unlike the problem of representation, will require something like the double aspect approach. Spinoza proposes the aspects of mind and body, Fodor proposes the aspects of semantics and syntax. That Fodor is a realist about representations and I am an eliminativist does not turn out to mean that we fundamentally disagree. Specifically I don’t think that syntax entails symbol entails semantics, a line of criticism that many materialists would take against Fodor. However, while Spinoza and Fodor both point the way to the resolution of the problem of rationality, to actually get there we must now consider the metaphysics of one of the greatest of all philosophers.

The Problem of Rationality, the Other "Problem of Intentionality"

What is the property of “rationality”? Let us say that it is a property of a rational being such that that being can make general use of an understanding of logical and mathematical functions and relationships. Rationality is a necessary component of agency (Kant stresses this): the reasons for the action can only be described with respect to the logical implications that obtain between them (and thus Kant offers a “coherence” theory of truth). Of course ultimately there are physical reasons for everything: one has to eat. “Reason is the slave of the passions,” wrote Hume, and he is right. However, the ability to grasp logical entailments is, as Chomsky, a self-styled “Cartesian rationalist” would say, “generative,” just as logical relationships are themselves non-specific. “If X, then Y.” “X.” The inference to be made from the coincidental truth of these two propositions is the same regardless of what “X” and “Y” are. Humans are able to formalize math and logic, abstracting from concrete incidents in order to be able to study these formal relationships as such. And, although my sympathy with Hume is great and my antipathy towards human exceptionalism equally so, the fact is that empiricism has a hard time dealing with mathematical and logical thought (I will use the term “rational” to refer to this kind of formal thinking for the sake of economy; in any event I think that logic and mathematics are the same thing). The kind of knowledge generated by rational thought (for example the proof of the infinity of prime numbers) appears to go beyond anything that could be explained as the product of interaction with the environment.

The idea that the propositional contents of intentional states are the bearers of logical relationships with each other is an expression of this problem: physical states and processes don’t appear to have any logical relationships whatever, whether they are “in the head” or not. However, this problem is a separate problem from the problem of mental representation, for whether one endorses a representational model of the mind or not one must still acknowledge the supervenient nature of rationality.

In fact the multiple realizability of rationality is the core metaphysical problem here. The problem can be stated this way: there do not appear to be any physical criteria that fix the extension of the set of rational beings. Flipper the dolphin, Max the Martian, Hal 2000 the intelligent artifact and I all take intentional predicates that entail the rationality assumption even though we’re not all made of the same sort of stuff. Although all four of us have physical properties sufficient to instantiate rationality, none of these physical properties are necessary for rationality (since we don’t share them). The extension of our set is indefinitely large.

A common popular view is that emotional experience and feeling are what make the naturalization of psychology so difficult, but philosophers and psychologists from the ancient Greeks on have more frequently taken humans’ rational capacity as the principal warrant for dualism. In fact both of the two greatest rationalists, Plato and Kant, saw emotions as fundamentally physical in origin, “passions” of the soul (like hunger) that sprang from our contingent natures as physical things. Plato and Kant also agreed that the capacity for rational thought was the key to human freedom, which they defined as freedom from the coercion of physical cause-and-effect relations. Both thought that qua embodied beings humans were mere material things, but through participation in transcendent rationality humans became (or could become) more than mere things.

I doubt that being motivated by purely logical thoughts (whatever that would be like; I suspect it’s inconceivable: and see Chapter Four) would result in anything recognizably like our usual conception of “freedom.” After all logical entailments follow necessarily from their antecedent propositions, so that to the extent that one is motivated by purely logical considerations one does not experience choice (or possess any psychological individuality for that matter). But putting the question of freedom aside, it does look like emotional experience is part of consciousness (emotions are essentially phenomenal) whereas rational thought is part of intentionality. Anyway that view, and the view that phenomenal “properties” of mind are, ontologically speaking, identical to physical properties of the body, will be defended in Chapter Three.

It turns out that understanding a difference between Plato and Kant is the key to the resolution of the problem of rationality when viewed as one of the mind-body problems. Before elaborating that difference, however, it will be useful to lay some groundwork by considering the views of two other great rationalists.

An Externalist Account of Intentional Predicates

Consider Hilary Putnam’s “Twin Earth” argument. Imagine, the argument goes, a Twin Earth: one that is molecule for molecule identical to this Earth. Of course you will have a Twin Earth doppelganger, molecule for molecule identical to yourself. On a reductive materialist account, granting that you have physically identical brain states it follows that you have psychologically identical mental states. For example you will have identical beliefs about water, the colorless, odorless substance that is ubiquitous in your parallel worlds. But imagine that there was just one difference between Earth and Twin Earth: on Earth water is composed of H20, but on Twin Earth water is composed of XYZ. Now everything about you and your doppelganger – both your physical states and your mental contents – are identical, but they’re not the same. Your beliefs may be correct and his/hers false (he/she may believe, as you do, that water is H20), but at a minimum they are about different things. Thus the actual meaning of an intentional state cannot be determined either by its physical properties or, startlingly, by its mental properties (its causal properties that can only be explained with reference to its contents).

Another gedanken from Putnam: Imagine an ant is walking in the sand, behaving normally for an ant for the usual ant reasons. It leaves a trail that resembles a portrait of Winston Churchill. Is this a representation of Winston Churchill? No it is not, even though it has the same physical properties as an actual sketch of Winston Churchill: how it came to be is relevant to its status as a representation. Something is not a representation by virtue of resemblance alone: Winston Churchill, after all, is not a representation of a sketch of himself or of an ant trail that looks like him.

Putnam’s famous slogan is “meaning just ain’t in the head.” The meaning of an intentional state is determined not only by physical and mental properties intrinsic to the subject (“in the subject’s head”) but also by facts about the environment and the subject’s relationship with the environment. This view is called “externalism,” and is also referred to as the “wide content” view: the view that intentional predicates refer to relationships between the nominal subject of intentional predication and their environment.

The representational theory of mind is deeply entrenched and some disambiguation is necessary to avoid outlandish interpretations of externalism and its claims. In this book I am examining the meanings of psychological predicates; in this chapter, intentional predicates. So for me the “meaning” in question is the meaning of words like “believes,” “desires,” “hopes,” “fears” and so on, in the sense of ontological reference: what ontological commitments do we make when we use these words? When Putnam says that “meaning isn’t in the head,” he isn’t talking about the meaning of the word “belief” (my topic), he’s talking about meaning in the sense that the alleged proposition that is the alleged object of the attitude is supposed to be about something: the proposition is the thing that is about something, on the representational realist view, and the proposition is represented “in the head.”

It is a consequence of externalism that beliefs (or any intentional states) aren’t about anything at all. That’s not how they work. They’re not even about the world, let alone internal representations of the world, because what they actually (ontologically speaking) are are relationships between persons and their environments, and relationships aren’t about anything, any more than physical objects or dispositions to behave are about anything. And that is exactly what naturalization requires: that there is no longer any reference to anything that “means” anything, meaning being a non-physical and therefore non-existent “property.” On a functional-role semantics words themselves aren’t about anything, not even proper nouns, so they can’t serve as magical vessels of meaning as they do on a traditional view. Language is a way that persons have of doing things - whole embodied persons situated in particular environments.

Here I am going beyond Putnam (undoubtedly an unwise thing to do!), because Putnam helps himself to mental content even as he argues that mental content alone is not sufficient to determine meaning. But if meaning, understood as “wide content,” turns out to be a description of relationships between persons and environments then there cannot be any mental content. There are no propositions transcendently emanating from Platonic heaven whether or not some person adopts an attitude towards them. There are only specific, concrete instances of states of affairs (I will use “states of affairs” as a more economical way of saying “relationships between persons and their environments;” this is consistent with the more standard use of the phrase as referring to ways the world could be) and goal-directed, token incidents of language-use.

Is Santa Claus a problem? Can’t one be thinking about Santa Claus even though Santa Claus is not part of the environment? No, Santa Claus is not a problem because Santa Claus is a cultural convention and that counts as part of the environment. One is thinking, in the Santa Claus case, not about a mythical character that is actual because mythical characters are not actual. That’s what “mythical” means. As for misrepresentation (as in the case of the five-year-old who believes that Santa Claus is actual), this is something that can only be demonstrated operationally.

What about a person or creature or what have you that exist only in the imagination of one individual? A stranger who appears in a dream, say? Here the right response is to remind ourselves that we are talking about the semantics of intentional predication, not about private experience. In fact the argument is that there can be no public description of private experience; remember Wittgenstein’s beetle-in-the-box. Note that, to the extent that “interpreting representations” is thought of as a process with a phenomenal component (after all, mustn’t there be “something that it’s like” to interpret a representation?), the putative experience of a representation (can one interpret a representation without experiencing it?) cannot be the criterion for proper intersubjective use of the word (see the discussion of phenomenal predicates in Chapter Three).

But surely dreams are evidence of mental representation? Aren’t dreams, in fact, just direct experiences of mental representation? No: although mental processes often involve experiences that seem similar to inspecting representations, remember that there is no explanatory value in literally positing mental representations. They don’t help to explain dreaming any more than they help to explain perceiving, remembering or imagining. In fact they make the model of the mental process considerably more complicated and difficult; a good reason for denying them. Berkeley thought that to clear up the Lockean mess of properties of objects-in-themselves, properties of objects to cause perceptions, and properties of perceptions, either the “mental” or the “external world” had to go. On that point he was right.

A little bit more disambiguation: my intentions here are perhaps deceptively arcane. I am focused on the metaphysics of the mind-body relationship. When I argue that, metaphysically speaking, there are in fact no such things as “mind” or “meaning,” I am arguing that traditional notions of those concepts are currently misleading us in our efforts to understand how the nervous system works. I don’t think any radical change in the way we talk is called for. In fact it is my view that a great deal of our psychological talk is ineliminable, and I think this goes for “mind,” “reference” and “meaning” just as much as for “belief” and “desire” and “beauty” and “justice,” and for the same reasons. If one accepts the present argument against mental representation, it still makes as much sense as it ever did to ask “What are you thinking about?” or “What is that book about?” or “What does that word mean?” The metaphysical question is about the proper semantic analysis of the way that we have always talked; that is nothing like a critique. As Wittgenstein said, “Philosophy changes nothing.” If the present proposal that intentional predicates pick out relationships between embodied persons and their environments is sound then that has always been what we have been doing. Jettisoning realism about mental representations is a substantial matter for cognitive science – I would stress the importance for developing experimental paradigms in brain science – but it’s hard to see how it could have any effect on popular usage of intentional terms.

To summarize, intentional predicates are applied to whole persons in particular environments, not to brains or nervous systems or neural processes or any physical part of persons. Perceiving, imagining, thinking, remembering and so on are the kinds of things that whole persons do. Among these intentional activities is interpreting. Symbols are interpreted by persons, and thus symbols must be located where persons are located: in the world. It follows that language, a symbol system, is a feature of the person’s environment as well: there are no symbols in the head. There is not, ontologically speaking, any such thing as meaning: there are only particular acts of persons negotiating their environments with use of sounds and symbols (and, following the mereological fallacy argument, this will be true of all language use including idle musings, random thoughts etc). The use of the word “meaning” as applied to intentional predication (“What is he thinking about?” “What does she know about gardening?” etc) is partially constituted by facts about the environment (pace Putnam). The natural semantic for intentional predicates is that they refer to relationships between individuals and their environments. If the account given here is persuasive there cannot be any such things as “mental representations.”

Propositional Attitudes

When Bertrand Russell coined the phrase “propositional attitude” in his 1921 book The Analysis of Mind, he wasn’t thinking of “proposition” in the sense of a piece of language. He was thinking that what was represented was a situation or what would today most likely be called a “state of affairs,” a way the world could be. However several considerations led subsequent philosophers of mind to take a much more literal view of propositions as linguistic entities and as the objects of the attitudes.

Think of a tiger. Alright: now, how many stripes does your imaginary tiger have? Probably your “mental image” of a tiger turned out not to have a specific number of stripes. But a pictorial representation of a tiger would have to. Linguistic (formal) systems can include relevant information and need not contain irrelevant information, an obvious adaptive advantage over isomorphic (pictorial) representation. Formal representation was more congenial to the operationalists (such as computationalists) who wanted to develop functional models of cognition. Then in the late 1950s the linguist Noam Chomsky, critiquing behaviorism, made the enormously influential proposal that formal syntactical structure was “generative”: grammatical forms like “The_is_the_” allowed for multiple inputs and thus indefinitely many (linguistic) representations. Taken to its extreme this argument appears to show that it is necessary for a being to have a formal system for generating propositions to be capable of being in an intentional state at all. Finally the argument that it is propositions that have the property of meaning and that it is propositions that bear logical relations to each other made it seem that a linguistic theory of representation made progress on the mind-body problem.

On my view this is mistaken: the representational model of mind, by definition, locates “mental content” “in the head.” The basic metaphysical problem with the representational model has by now been made clear: “meaning,” what I have been calling the “intentional property” or the “semantic property,” is an irredeemably non-physical “property” that must be washed out of any naturalistic theory of mind. Once one recognizes that intentional predicates are predicated of whole persons – once one sees that positing mental representations necessarily commits the mereological fallacy – the matter is settled. However there is a tight network of arguments and assumptions about intentional states as “propositional attitudes” that will have to be disentangled to the satisfaction of readers who are disposed to defend representations.

The defender of propositional attitudes will start by pointing out that intentional states can only be individuated by virtue of their respective contents. What makes Belief X different from Belief Y is that X is about Paris and Y is about fish. This looks like a block to reduction: to correlate electrochemical activity in the brain, say, with Belief X, we must already be able to specify which belief Belief X is. We don’t have any way of getting from no-content to content (from the non-mental to the mental). This motivates the problem of mental causation: it appears that the content (meaning) of the proposition is what plays the causal role in the production of behavior: when told to proceed to the capital of France he went to Paris because he believed that “Paris is the capital of France.” All the explanation in physical (neurophysiological) terms one could possibly make wouldn’t be explanatory if it didn’t at some point reveal the meaning that is expressed in the proposition, and it doesn’t: “He believes that Paris is the capital of France” is not shorthand for a causal chain of neurophysiological processes.

Donald Davidson famously pointed out a further problem for the development of “psychophysical laws” (as he called them), laws that systematically identified brain processes with particular instances of intentional thought: no one propositional attitude could ever suffice as the discrete cause of a behavior because the causal implication that the propositional attitude has for the acting subject necessarily emerges from the logical relations that that “attitude” has with all of the other intentional states of the subject. Davidson’s phrase for this was “meaning holism,” the view that meaning (in the sense of explanatory psychological predication) is a property of networks of propositional attitudes, not of individual ones. There is not an assortment of individual intentional states in a person’s mind such that one or another might be the proximate cause of behavior; each person has one “intentional state,” the sum of the logically interrelated network of propositional attitudes.

Propositions are the bearers of logical relations with each other. Physical objects and processes, the argument goes, have no logical relations with each other. To believe that the drinking fountain is down the hall is to have the attitude towards the proposition “The drinking fountain is down the hall” that it is true, and to have a desire for water is to have the attitude towards “I have water” that one wants to make that proposition true. The explanatory utility of the intentional predicates – in this case the ability to make an inference from their coincidence that, all other things being equal, the subject will form an intention to walk to the fountain (that is, to make the proposition “I have walked to the fountain” true) – depends on the meaning of the propositions.

Of course making such an inference from the logical relationship between the two propositions also requires that we make a rationality assumption: we must assume about the subject that he, too, will appreciate these logical relations. That is part of the metaphysical “problem of rationality.” I cannot pretend that the distinction between the problem of rationality and the problem of representation is entirely clear-cut, but at this point I need only present a semantic for intentional predicates that locates logical relations out in the world rather than in the head; that will suffice to defeat the argument that mental content is necessary to explain the causal role of intentional states. The further metaphysical problem about the supposed lack of any correlation between the (contingent) physical relationships between states and processes in the body and the (necessary) logical relationships between propositions is dealt with in the discussion of the problem of rationality that is the second half of this chapter.

The terminal station for the line of argument that meaning is an indispensable property (and thus that representations are an ineliminable feature) of intentional explanation is Platonic realism about propositions. On this view, their role as individuators of intentional attitudes and as bearers of logical relations demonstrates that propositions are matter-independent, mind-independent “abstract objects,” ineliminable from ontology. Taking concrete sentences as the “tokens” and propositions as the “types,” the Platonic realist argues that propositions resist a standard nominalist treatment: a “proposition” cannot be simply the name of the set of all of the concrete sentences that express it. The Platonic realist appeals to our intuition that an unexpressed proposition is still a proposition. The fact that propositions can be translated into multiple languages is taken as a demonstration that propositions are not identical to their concrete sentence exemplars.

Wittgenstein proposes an alternative, behaviorist account of language. Wittgenstein’s famous dictum is that meaning is use. The “meaning” of a word, on this view, is whatever the user (speaker or writer) of the word accomplishes by the action of using the word. This alternative to traditional theories of meaning is often called “functional-role semantics.” Wittgenstein rejects the Platonic picture of concepts as essences: the property-in-itself, as distinct from any and all of the concrete exemplars of the property. Language use, he argues, is a type of behavior that reflects a “mode of life,” in the present case the mode of life of human beings. There are no essential meanings (there is no such thing as “meaning” in the traditional sense at all), just patterns of human behavior that can be roughly sorted out on the basis of resemblances and shared histories (these are language “games”). We may gather together statements about “justice” and note that they have similar contexts of use and similar implications for action, just as all of the members of a family can be linked through chains of family resemblance, but that is all. There can be no representation of justice because there is nothing to represent, just as a family of human beings has no “family avatar.” This argument generalizes to all words and their uses, not only those that we think of as naming “concepts.”

If this is right then we are entitled to nominalism about “propositions” after all. A proposition is nothing more than all of the sentence-tokenings of that particular string of symbols. In fact language loses its supposed “interior,” the meaning traditionally supposed to be within or behind the symbol, just as “mind” can now be seen as intelligible patterns of behavior of persons rather than as something “in the head.” Wittgenstein’s vision was to see everything as surface only, both in the case of mind and in the case of language. Psychological description and explanation, understood as an intersubjective discipline limited by the limits of language itself, was necessarily operational.

Now I can sketch out the first natural semantic, the one that replaces intentional predicates that attribute mental representations to persons.

The mereological fallacy

Stomachs don’t eat lunch. Eating lunch is something that a whole, embodied person does. We understand the role that stomachs play in the lunch-eating process; we appreciate that people can’t eat lunch without them. Brains don’t think. They don’t learn, imagine, solve problems, calculate, dream, remember, hallucinate or perceive. To think that they do is to commit the same fallacy as someone who thought that people can eat lunch because they have little people inside them (stomachs) that eat lunch. This is the mereological fallacy: the fallacy of confusing the part with the whole (or of confusing the function of the part with the telos, or aim, of the whole, as Aristotle, who once again beat us to the crux of the problem, would say).

Nor is the homunculus a useful explanatory device in either case. When I am asked how we might explain the workings of the mind without recourse to mental representations, the reply is that we fail to explain anything at all about the workings of the mind with them. “Remembering my mother’s face is achieved by inspecting a representation of her face in my mind.” This is explanatorily vacuous. And if reference to representations does nothing to explain dreaming, imagining and remembering, it is particularly egregious when mental content is appealed to for an explanation of perception itself, the original “Cartesian” mistake from which all of the other problems derive. A person is constantly developing and revising an idea of his or her world; you can call it a “picture” if you like (a “worldview”), but that is figurative language. A person does not have a picture inside his or her body. Brains don’t form ideas about the world. That’s the kind of thing people do.

This original Cartesian error continues to infest contemporary cognitive science. When the brain areas in the left hemisphere correlated with understanding speech light up and one says, “This is where speech comprehension is occurring,” the mereological fallacy is alive and well. Speech comprehension is not something that occurs inside the body. Persons comprehend speech, and they do it out in the “external” world (the only world there is). Positing representations that exist inside the body is an instance of the mereological fallacy, and it is so necessarily, by virtue of the communicative element that is part of the definition of “representation,” “symbol” etc. Neither any part of the brain nor the brain or nervous system considered as a whole interprets anything. The key to a natural semantic of intentional predicates is the realization that they are predicated of persons, whole embodied beings functioning in relation to a larger environment.

This realization may also be momentous for brain science. Go to the medical school bookstore, find the neurophysiology textbooks and spend a few minutes perusing them. Within the first minutes you will find references to the movement of information (for example by the spinal column), maps (for example on the surface of the cortex), and information processing (for example by the retina and in the visual cortex) and so on. (Actually I suspect that brain scientists are relatively sophisticated in their understanding of the figurative nature of this kind of language compared to workers in other areas of cognitive science; the point is just that representational talk does indeed saturate the professional literature through and through.) But if brain function does not involve representations then we don’t know what brains actually do, and furthermore the representational paradigm is in the way of finding out: the whole project needs to be reconceived. If there is any possibility that this is true at all then these arguments need to be elaborated out as far as they can be.

Taking the argument from the mereological fallacy seriously also draws our attention to the nature of persons. It follows from what has been said that the definition of “person” will be operational. Operational definitions have an inevitably circular character: a person is any being that takes intentional predicates. One might object that we routinely make intentional predications of, say, cars (“My car doesn’t like the cold”), but as Daniel Dennett famously pointed out this objection doesn’t go through when we know that there is a “machine-language” explanation of the object’s behavior: I may not know enough about batteries, starters and so forth to explain my car’s failure to start in the cold, but someone else does, and that’s all I need to know to know that my “intentional” explanation is strictly figurative. But then don’t persons also have machine-language explanations?

No: my car won’t start because the battery is frozen. The mechanic does not commit any fallacy when he says, “Your battery’s the problem.” The part is not confused with the whole. It’s really just the battery. Now suppose that you are driving down the freeway searching for the right exit. You remember that there are some fast-food restaurants there, and you have a feeling that one always thinks that they have gone too far in these situations, so you press on. However you manage to do this, it is no explanation to say that you have done it because your brain remembered the fast-food restaurants, and has beliefs about the phenomenology of being lost on the freeway, and decided to keep going and so forth. That’s like saying that you had lunch because your stomach had lunch.

In fact there is not a machine-language explanation of personhood. Kant, writing in the late 1700s, is fastidious about referring to “all rational beings,” he never says “human beings”; he understands that when we are discussing the property of personhood we are discussing (what I would call) a supervenient functional property (Kant would call personhood “transcendental”), not a contingent physical property. Unfortunately Kant is programmatically intent on limiting the scope of materialism in the first place and thus fails to develop non-reductive materialism. But he understood that the mental cannot be one of the ingredients in the recipe for the mental.

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.

The modern history of representation

So internalized is the representational view that one can forget that it didn’t have to be this way. The history of psychology is, like all histories, full of contingencies and precipitous forks in the road. In the study of the history of Western philosophy we call the 17th and 18th centuries the “Early Modern” period, and the contemporary idea that we live in our heads, experiencing only a mental representation of the world, dates from this period. It was an incredibly fertile period for European philosophy: if we take, as most do, Descartes to be the first canonical Early Modern philosopher and Kant to be the last, the whole period is a scant 154 years (from the publication of The Discourse on Method in 1637 to the publication of The Critique of Pure Reason in 1781).

The adjective “Cartesian” literally means that an argument or position reflects the ideas of Descartes, but it has become through usage a more general term that alludes to representational theories of mind, particularly those theories that entail that we must worry about the relationship between the external world and a perceiving subject’s representation of the world – theories that “explain” perception as the formation of representations. This is not entirely fair to Descartes, who wrote in his Dioptics that it would be a mistake to take the inverted image observable on the retina as evidence that there were pictures in the mind, “as if there were yet other eyes in our brain.”

Even if the real Descartes was not someone who today we would call a Cartesian, he can certainly be held responsible in large part for the conspicuous lack of naturalism about psychology in modern philosophy: he was a metaphysical dualist, he thought that humans’ rational capacity comes not from nature but from God (notoriously he made this argument after arguing that he could prove God’s existence through the exercise of rationality), and he was a human exceptionalist who took language as evidence that humans are essentially different from the rest of the natural world. But the real “Cartesian” in the sense of the true ancestor of modern representational theory is Kant.

Kant’s explicit project was to block the naturalization of psychology. He was alarmed by what he saw as the atheistic, amoralist implications of Hume’s empiricism (implications emphasized by Hume himself). Hume’s whole oeuvre can be read as a sustained attack on the very idea of rationality: there are no “rational” proofs of anything, no “rational” reason for believing in anything. Beliefs are the product of “habituation,” the conditioning effect of regularities of experience. Thus there was no basis, on Hume’s view, for asserting the existence of God, of human freedom, or even of the human mind if by that was meant something over and above the contents (the “impressions”) of thought processes, which were the products of experience. Kant seems to have been intuitively certain that these radical conclusions were false, although he was criticized (by Nietzsche for example) for a programmatic development of foreordained conclusions.

Hume’s psychology was inadequate. Like Locke before him he thought that mental content could be naturalized if it was explained as the result of a physical process of perception: interaction with the environment was the physical cause of the impression, a physical effect. This strategy led the empiricists to emphasize a rejection of innate content, which they regarded as a bit of bad rationalist metaphysics. The problem was compounded by a failure to distinguish between innate content and innate cognitive ability. To some extent this failure reflected a desire to strip psychology down to the simplest perception/learning theory possible in the interest of scientific method, coupled with a lack of Darwinian ideas that can provide naturalistic explanations of innate traits (I will address the skeptical, “phenomenalist” reading of Hume, that I think is incorrect, in Chapter Three).

Kant saw this weakness and was inspired to develop the argument of the Critique of Pure Reason. Hume claimed that all knowledge was the result of experience. Kant’s reply was to ask, “What is necessary in order for experience to be possible?” The greatness of Kant is in his effort to backwards-engineer the mind. He is best read today as a cognitive scientist. However people forget how radical Kant’s conclusions were, and how influential they have continued to be, one way or another, to virtually all philosophers and psychologists since the late 18th century. From the persuasive argument that the mind must somehow sort and organize the perceptual input (that’s the part of psychology that the empiricists’ ideology led them to neglect), Kant goes on to argue that space, time, cause and effect relations and the multiplicity of objects are all part of the “sensible” frame that the mind imposes on our experience of the world. The world of our experience is the phenomenal world, and it is that world that is the subject of natural science; the world-in-itself is the noumenal world (and quite the bizarre, Parmenidean world it is!).

Two points are important here. First, Kant’s aim was to protect human psychology (and religion and ethics) from a godless, amoral, reductive natural science and in that he succeeded to an alarming extent. The world of natural science on the Kantian view is the world as it is conceived by the rational mind, and as such the rational mind itself cannot be contained in it. Second, Kant’s biggest contribution of all is easy to miss precisely because it is so basic to his whole line of argument: the phenomenal world is a representation, made possible by the framing structure of rational conception, just as the drawing on the Etch-a-Sketch depends on the plastic case, the internal mechanism and the knobs of the toy.

The defender of Kant will argue that the Kantian phenomenal world is not a representation at all: it is the world presented to us in a certain way. It is also only fair to point out that Kant, unlike his modern descendents, shared with Plato the view that all rational minds were identical to the extent that they were rational. Kant would not have been amused by 20th century philosophers’ pictures of a world where each language, culture and individual were straying off, like bits some expanding universe, into their private “conceptual schemes,” ne’er the twain to meet. Nonetheless Kant needs mental representation (and any conceptual schemata is representational), because he needs to protect freedom, rationality, God and ethics. Thus a deep skepticism is intentionally built in to Kant’s system (as it is not in Descartes’). While Kant is right in a great many things and any student of philosophy or psychology must read and understand him, on these two points his influence is ultimately pernicious.

I dilate on the Kantian history of the representational theory because once we see that the issues that confront us in philosophy of mind continue to be essentially metaphysical we also see that they are very old issues, and ones that connect up with many other perennial philosophical problems. Too many people in contemporary philosophy of mind and cognitive science fail to appreciate this and the discussion is very much the poorer for that. Furthermore it’s important to see that things didn’t have to be this way. The idea that we are stuck in our heads with our “representation” of the world forever mediating between us and “reality” is actually a very strange idea, but it has been so deeply internalized by so many that we can fail to appreciate how strange it is. This is something to bear in mind as we think about how modern physicalist philosophy of mind has struggled with the problem of mental representation.

The Problem of Mental Representation

People tend to be of two minds (pun intended) on the issue of mental content. On the one hand no one can dispute that the way we talk about the mind is largely figurative. The mind is racing and wandering, it has things on it and in it, it is sometimes full and sometimes empty, it is open and narrow and dirty and right. We are used to talking this way, it is useful to talk this way (I don’t think there is anything wrong with our psychological talk), and everybody pretty much understands that this is a discourse full of “figures of speech.” The philosophically-inclined see well enough that “mind” is an abstract concept of some sort. On the other hand we have deeply internalized some of this figurative language, so deeply that one of the most central, perennial problems of epistemology is the alleged problem about the relation of our “inner” perceptions of the world to the “real world” out there, outside of our heads. Many people think that we are stuck inside our heads: a blatant conflation of the literal with the figurative.

Why is this? For one thing when we talk about the mental we must use the language that we have, and this is a language evolved for talking about the physical, “external” world of three-dimensional objects in three-dimensional space. The room has an inside and an outside, and there are things (concrete things) inside it (those chairs and tables that philosophers are always talking about). “Beliefs” and “sensations” are words that take the same noun-role as “chairs” and “tables,” and thus the grammar of the language is constantly pushing us to conceive of these mental terms as referring to some variety of concrete things. This is the sense in which Wittgenstein uses the word “grammar”: to indicate the way that language contains metaphysical suggestions that can lead to confusion. The metaphysical grammar of language is the grammar of three-dimensional objects in three-dimensional space; objects, moreover, that interact with each other according to regularities of cause and effect.

A basic confusion about the mind is that it is a kind of inner space filled with things and (non-physical) processes. It is important to see the close relationship between this pseudo-spatial conception of the mind and the problem of mental representation. Physical things and processes don’t mean anything (or, physical descriptions and explanations of the things and processes in the world don’t refer to the semantic property, only to physical properties). The concept of a symbol is essentially relational: symbols need to be interpreted. For interpretation to happen there must be an interpreter. Pictures, books and computer screens need to be looked at by someone – someone with a mind. Thus the representational model has a “homunculus” problem: in order for the symbol to work it must be read by someone, as streetlights and recipes only “work” when actual people respond to them with appropriate actions. Another way of putting the problem is the “regress” objection: if the theory is that minds work using representations, then the homunculus’s mind must work that way as well, but in that case the homunculus’s mind must contain another homunculus, and so on.

Some cognitive scientists have tried to overcome this objection by suggesting that a larger neural system of cognition can be modeled as responding to information from neural subsystems without succumbing to the homunculus fallacy, but this strategy can’t work if a “representational” theory of mind is one that posits representations as necessary for thought. A theory of mind that succeeds in naturalizing psychology will be one that shows how the “mental” emerges from the non-mental. Any theory that includes anything mental in the first place accomplishes nothing. The concept of a representation is a mental concept by definition: the verb “to represent” presumes the existence of an audience. Representation, like language, cannot be a necessary precondition for thought for the simple enough reason that thought is a necessary precondition for both representation and language (a being without thoughts would have precious little to talk about!). This is not a chicken-and-the-egg question.

There is an important discussion here with the computationalists, who think that the mind/brain is a kind of computer. If it is the representations that bear logical relations to one another (the computationalist argues), and rationality consists in understanding and respecting those relations, then rationality requires a representational (typically thought of as some sort of linguistic) architecture. If computation is formal rule-governed symbol manipulation then symbols are necessary for computation/cognition. Jerry Fodor, for example, hopes to bridge mind (intentional explanation) and body (physical explanation) by way of syntax, the formal organization of language. The idea is that all of the causal work that would normally be attributed to the content of the representation (say, the desire for water) can be explained instead by appeal to “formal” (syntactic, algorithmic) features of the representation (there is some more discussion of Fodor below).

One challenge to this computationalist (or “strong AI”) view is connectionism, the view that the mind/brain has an architecture more like a connectionist computer (also called parallel distributed processing, PDP; in the wetware literature this is the “neural nets” discussion). In connectionist computing, systems of nodes stimulate each other with electrical connections. There is an input layer where nodes are activated by operators or sensors, programming layers where patterns from the input layer can be used to refine the output, and the output layer of nodes. These connections can be “weighted” by programmers to steer the machine in the right direction. Some of these systems were developed by the military to train sonar systems to recognize underwater mines, for example, but they are now ubiquitous as the face-, handwriting- and voice-recognition programs used in daily life.

Connectionist machines are very interesting for purposes of the present discussion. They appear to be self-teaching, and they appear to function without anything that functions as a symbol. There is still the (human) programmer and there is still nothing that seems like real consciousness, but such a system attached to a set of utilities (so far, the utilities of the programmers) looks to be effective at producing organized behavior and fully explicable in operational terms.

Meanwhile, I’m not even sure that computers have representations in the first place. That is, it’s hard to see anything that functions as a representation for the computer (which is not surprising since it doesn’t look like the computer has a point of view). What makes computers interesting to cognitive science in the first place is that with them we can tell the whole causal story without appeal to representations: the binary code just symbolizes (to us) the machine state (the status of gates in the microprocessors), and we can sustain the machine-level explanation through the description of the programming languages and the outputs. Those “outputs,” of course, are words and images interpreted by humans (mostly). So even “classical” computers do have computational properties and do not have representations. Or perhaps another way to put it is that two senses of “representation” are confuted here: the sense when a human observes a computational process and explains it by saying: “See, that functions as a representation in that process” and the sense when a human claims to interpret a representation. (I will discuss computational properties as “formal” properties in the discussion of the problem of rationality below.)

The computationalist/connectionist discussion is a striking example of how little the larger discussion has changed since the 17th century. It is the rationalist/empiricist, nativist/behaviorist argument rehearsing itself yet again through the development of this technology.

The Problem of Intentionality

In the last chapter I argued that there is no one thing to which the word “mind” refers. I argued further that there are (at least) two metaphysical problems that are still unresolved in our psychological talk; two kinds of putative mental “properties” that each, in their respective ways, resists naturalization. It may be, though, that spelling out the heterogeneity of mind is progress: for much of the dissatisfaction with operationalist theories is because of their manifest failure to give a satisfactory account of consciousness, while any straightforward materialist account of consciousness appears to run afoul of the issue of “multiple realizability” and “chauvinism.” Once we accept that we have two different topics it may turn out that our current theories are not as inadequate as they seemed; they are only more limited in their scope than we had assumed.

If this is right then one who is interested in the problem of intentionality needn’t necessarily be interested in the problem of consciousness or vice versa. What appeared to be a fairly violent doctrinal schism between the operationalists and the phenomenologists is revealed to be a mere changing of the subject. Of course if a naturalistic semantic of intelligence-predicates and a naturalistic semantic of consciousness-predicates are both necessary but neither sufficient for a complete naturalistic semantic of psychological predicates, then analyses of both semantics will have to be offered. But each semantic and its defense should be free-standing if the heterogeneity argument in the last chapter is true.

The problem of intentionality itself decomposes further into two interrelated but distinguishable problems. The first is the problem of mental representation. Symbols of any kind (including isomorphic representations like paintings and photographs and formal representations like spoken languages and computer codes) have, it seems, the property of meaning (that I will usually call the semantic property or, interchangeably, the intentional property). Symbols refer to, are about, things other than themselves (the neologism “aboutness” also expresses this property), while physical things (or things described and explained in physical terms) do not have any such property (the descriptions and explanations include only physical terms). A naturalized semantic of psychological predicates would be free of reference to non-physical properties, but even our current neurophysiology textbooks have information-processing models of nervous system function (and the popular conception of the mind is of something full of images, information and language).

The operationalist theories of mind developed by English-speaking philosophers during the 20th century are largely a response to the problem of representation, although there are a variety of conclusions: behaviorism is straightforwardly eliminativist about mental content, limiting the possible criteria for use of psychological predicates to intersubjectively observable things. Computationalism, insofar as it holds that minds are formal rule-governed symbol-manipulating systems, aims at radically minimizing the symbol system (as in binary-code machine language for example) but remains essentially committed to some sort of symbolic architecture. Functionalism proposes a psychology that is described purely in functional terms rather than physical terms, which provides for replacing representations with functionally equivalent, non-representational states, but in its very abstraction functionalism does not commit to eliminating representations (functionalism may be more of a method than a theory). In the first half of this chapter I will draw on the work of some latter-day philosophers, generally influenced by Wittgenstein, to develop a semantic of intentional predicates that not only dispenses with any references to mental representation (as behaviorism and functionalism do) but provides an account that actually rules out the possibility of mental content.

The other part of the problem of intentionality is the problem of rationality. Rationality is multiply realizable (a synonymous term is supervenient). To see what this means consider an example from another area of philosophy, “value theory” (an area that encompasses aesthetics and ethics): Say I have a painting hanging on the wall at home. This painting has a physical description, which lists all and only its physical properties: it is two feet across and four feet tall, weighs seven pounds, is made of wood, canvas and oils, is mostly red etc. Rarely, though, does anyone find these physical properties remarkable qua physical properties. Instead my visitors are likely to remark that the painting is beautiful, finely wrought, significant etc. The metaphysical problem is that these aesthetic properties cannot be analyzed into, reduced to or identified with the painting’s particular set of physical properties (notwithstanding the fact that my visitors will appeal to these physical characteristics, as in “That red tone is lovely,” when elaborating on their aesthetic judgment). The aesthetic properties surely emerge, somehow, from this particular combination of physical properties. There could be no change of the physical properties without some change in the aesthetic properties (this is the standard definition of the “supervenient” relationship). But not all objects with these physical properties are necessarily beautiful, nor do all beautiful things have these physical properties.

Rationality is a supervenient property. For example a human being, a dolphin, a (theoretically possible) rational artifact and a (probably existing) intelligent extraterrestrial all instantiate (that is, grasp and make use of) the function of transitivity (“If X then Y, if Y then Z, therefore if X then Z”). But these beings are made of various materials organized in various ways. There are no physical properties that fix the extension of the set of rational beings and so this set, like the set of beautiful things, is indefinitely large. Another way of saying the same thing is to say that there are no psychophysical laws regarding rationality, generalizations to the effect that any being with such-and-such logical capacity must have such-and-such physical characteristics or vice versa.

The problem of mental representation and the problem of rationality can be distinguished as separate metaphysical problems. We would still be confronted with the problem of rationality even if we did not subscribe (that is, if none of us subscribed) to a representational theory of mind. Nonetheless the two sub-problems should be grouped together under the general rubric of the problem of intentionality, because both are problems for the same set of psychological predicates, the intentional predicates: “believes,” “desires,” “hopes,” “fears” etc. Intentional predicates name states that apparently entail mental content, as one believes that X, fears that Y etc., and also apparently entail rationality, as it is only explanatory when I say to you of a person that he left the room because he was thirsty if we share the background assumption that, if he believes that there is water at the fountain and desires to have water then, all other things being equal, he will go to the fountain (this is commonly referred to as the rationality assumption).

Some philosophers will claim at this point that the necessity of the rationality assumption for intentional explanation blocks naturalization. The argument is that it is the propositions (“I have water to drink,” “There is water at the fountain down the hall”) that bear logical relations to one another. If these propositions are not identical to their various physical tokens then they are non-physical entities (this kind of view is often called “Platonic realism,” that is realism about non-physical entities). This argument also counts against my claim that the two problems of intentionality can be separated if it turns out that tokens of propositions are necessary for logical thinking.

A related worry that also apparently ties the two problems of intentionality together is about the causal role of content (“the problem of mental causation”): The man is running because he wants to get away from the tiger that is chasing him. If a physical description of his brain and the processes occurring there does not convey that he is being chased by a tiger, not only does it fail to provide the kind of explanation we want (we want to know the reason he is running), it also appears to fail to describe what is happening “in his own head,” since the perception of an attacking tiger is part of the cause of his action.

I think that I can provide a satisfactory response to the problem of propositions as bearers of logical relations, although the result is somewhat surprising in the context of the overall physicalist project of this book. However the problem of mental representation will be discussed first, because it is important to see that even if we were to reject the representational theory of mind (as I think we should) we would still be confronted with the problem of rationality. The question of rationality takes us a good deal further into general metaphysics.