Abstract
In their recent book Philosophical Foundations of Neuroscience, Max Bennett and Peter Hacker attack neural materialism (NM), the view, roughly, that mental states (events, processes, etc.) are identical with neural states or material properties of neural states (events, processes, etc.). Specifically, in the penultimate chapter entitled “Reductionism,” they argue that NM is unintelligible, that “there is no sense to literally identifying neural states and configurations with psychological attributes.” This is a provocative claim indeed. If Bennett and Hacker are right, then a sizeable number of philosophers, cognitive scientists, neuroscientists, etc., subscribe to a view that is not merely false, but strictly meaningless. In this article I show that Bennett and Hacker's arguments against NM, whether construed as arguments for the meaninglessness of or the falsity of the thesis, cannot withstand scrutiny: when laid bare they are found to rest upon highly dubious assumptions that either seriously mischaracterize or underestimate the resources of the thesis.
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Notes
Bennett and Hacker (2003). Unless otherwise noted, all page references are to this work. Largely positive reviews of the book have been written by, among others, Smith (2005), Robinson (2004), Pitici (2005), and Cockburn (2005). For mostly negative commentary, see Hodgson (2005) and Churchland (2005). For a reply to Hodgson, see Hacker (2005). Bennett and Hacker participated in an “Authors and Critics” session at the 2005 meeting of the American Philosophical Association in New York. Their critics were D. Dennett and J. Searle, whose work Bennett and Hacker vigorously attack in their book. The contents of that meeting have recently been published under the title Neuroscience and Philosophy: Brain, Mind, and Language (New York: Columbia University Press, 2007).
The notion of identity criteria is somewhat obscure; and some have even argued that the demand for identity criteria ought to be rejected altogether (e.g., Jubien 1996). Bennett and Hacker do not state what they mean by “criteria of identity,” so I shall assume that they think of themselves as deploying the concept as standardly conceived. On the standard conception, the criteria of identity for x are constituted by the necessary and sufficient conditions for being x. It should be noted, however, that there is another reading of “criteria of identity,” inspired by Wittgenstein, according to which to say that a condition C is a criterion for x is not to say that C is necessary or sufficient for x, but only that C bears a privileged epistemic relation to x – say, that C’s obtaining always provides justifying grounds for supposing that x has obtained, even if it does not entail that x has obtained (see §2 below). If Bennett and Hacker are to be understood as employing “criteria of identity” in this sense, however, their objection would founder most precipitously. For there is nothing barring a neural materialist from saying that any condition C that is a criterion (in this sense) for a mental state m is also a criterion for some neural state n. Suppose, for example, that C is a certain kind of behavior. A proponent of NM could say that this behavior is a criterion for m and hence also for some neural state n, since (according to NM) m = n.
According to some, multiple realizability arguments are just another kind of conceivability argument, rather than a fundamentally different argument strategy, and so it might be thought that disambiguating this objection as either a multiple realizability argument or a conceivability argument is redundant. However, I think it best to disambiguate the objection in this way, for although conceivability arguments and multiple realizability arguments both involve a modal claim—i.e., both assume that mental states may be multiply realized—the former appeal to conceivability to bolster the case for possible multiple realization, whereas the latter simply assert that it is possible for mental states to be multiply realized.
This is not the only (though it is my preferred) way of responding to the objection from multiple realizability. Others (e.g., Hill 1991; Braddon-Mitchell and Jackson 1996; Polger 2005) have argued that we should try to salvage type NM. Typically, supporters of this latter strategy argue that retaining type NM is preferable because token NM is too weak to serve as an adequate account of the nature of the mental. I am not convinced. Token NM says something significant about the nature of mental states, namely, that token mental states are identical with token neural states. And I suspect that further empirical investigation will provide sufficient evidence for us to reasonably conclude that different types of pain – e.g., sharp pains in the abdomens of human mammals – are identical with types of neural states. Since it is domain or species specific, this is not, perhaps, the kind of full-fledged type materialism that some are seeking, but it is nevertheless robust enough to be fully explanatory.
Many philosophers who endorse token NM are also functionalists, and so are keen to emphasize that mental property instances are identical with functionally organized neural property instances. On this view, mental states are functional states that have neurophysiological realizers. The main virtue of coupling token NM and functionalism is that it allows a proponent of NM to claim that even though mental property instances M and M* might be identical with different neural property instances, they are still subsumable under the same concept. For example, since both pain1 (say a human’s pain at t) and pain2 (say a reptile’s pain at t) fulfill a certain functional role in the life of the organism, the concept expressed by the term “pain” can denote pain1 and pain2 and yet remain the same concept, even though pain1 and pain2 are identical with different neural property instances.
Others, to be sure, have advanced arguments against NM that turn on the location of mental states. Descartes, for example, thought it problematic for mental states to be spatially located. As far as I know, however, Bennett and Hacker’s arguments put a novel spin on this line of attack on NM.
To be clear, my belief that it will rain—i.e., my psychological state pertaining to the predicted rain—is located in my skull, not what I believe. If I believe that it will rain, then what I believe is that it will rain, but that it will rain is nowhere in my skull. Similarly, if I believe the rumor, the testimony, the allegation, etc., then what I believe is the rumor, the testimony, or the allegation, but none of these is in my skull.
Bennett and Hacker extract from the work of Wittgenstein the insight that psychological predicates can legitimately be applied only to whole creatures. Wittgenstein expresses this insight most perspicuously with the following terse remark: “only of a human being and what resembles (behaves like) a living human being can one say: it has sensations; it sees, is blind; hears, is deaf; is conscious or unconscious” (1953, §281).
Some predicates, as Bennett and Hacker point out (p. 73), can apply to both a whole and to its parts. For example, there is nothing logically awry about applying the predicate “has cirrhosis” to both S and to S’s liver; and it makes perfectly good sense to apply the predicate “has gangrene” to both S and to S’s foot. But these cases are quite beside the point. The range of predicates under consideration—viz., psychological predicates—has no intelligible application to parts of a whole, i.e., to parts of a conscious creature.
Bennett and Hacker are not espousing any kind of behaviorism. Their claim is that behavioral criteria are partly, not wholly, constitutive of what psychological predicates mean.
Strictly speaking, we do not experience our beliefs, since beliefs are not experiential states at all. Nevertheless, it is not inappropriate to say that we experience our beliefs in the sense that we entertain them, think about them, put them in the “logical space of reasons,” etc.
Baker (1994) has also argued against NM on the grounds that mental states cannot be ascribed to parts of a conscious creature. “[A] belief, she claims, “is a global state of a whole person, not of any proper part of the person (such as the brain)” (1994, p. 192). But if, as NM claims, the person is the subject of the appropriate neural state (i.e., the neural state that happens to be identical with a mental state), the apparent conflict between construing beliefs as neural states and construing them as global states of whole persons disappears. On the one hand, beliefs are global states of whole persons, in the sense that the person is the subject of the belief: it is the person who believes that p, not the person’s brain. On the other hand, beliefs are (according to NM) also neural states. There is no inconsistency here.
It is worth noting that this objection cannot be averted by appealing to the view that the semantic content of a term, i.e., what it would contribute to a proposition, is its referent. If this view is correct, then co-referring terms are intersubstitutable salva veritate, even in intensional contexts, from which it follows that there is in fact a (disguised) contradiction in asserting that “I believe that lightning is p, but it is not the case that an electrical discharge is p,” since “lightning” and “an electrical discharge” have the same referent. This strategy fails because it can be deployed on behalf of NM; that is, it can be used to argue that since, according to NM, “a certain neural configuration in my brain” and “my belief that p” have the same referent, there is in fact a (disguised) contradiction in asserting “A certain neural configuration has obtained in my brain, but it is not the case that p.”
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Janzen, G. Bennett and Hacker on Neural Materialism. Acta Anal 23, 273–286 (2008). https://doi.org/10.1007/s12136-008-0031-3
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DOI: https://doi.org/10.1007/s12136-008-0031-3