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.