"Multiple Realizability," in D. Borchert, ed., The Encyclopedia of Philosophy, vol. 6, 2nd edition. US: Thomson Gale, Macmillan Reference, 2005, pp.427-432. [pdf] Multiple realizability has been at the heart of debates about whether the mind reduces to the brain, or whether the items of a special science reduce to the items of a physical science. For example, many claim that mental or computational properties are not reducible to physical or engineering properties because the former can be realized by the latter in so many different ways. But what does that mean? I break down the two central notions implied by the concept of multiple realizability: "multiplicity," otherwise known as property variability, and "realizability." Beginning with the latter, I distinguish three broad conceptual traditions. The Mathematical Tradition equates realization with a form of mapping between objects. Generally speaking, x realizes (or is the realization of) y because elements of y map onto elements of x. The Logico-Semantic Tradition translates realization into a kind of intentional or semantic notion. Generally speaking, x realizes (or is the realization of) a term or concept y because x can be interpreted to meet the conditions for satisfying y. The Metaphysical Tradition views realization as a species of determination between objects. Generally speaking, x realizes (or is the realization of) y because x brings about or determines y. I then turn to the subject of property variability and define it in a formal way. I then conclude by discussing some debates over property identity and scientific theory reduction where the resulting notion of multiple realizability has played a central role, for example, whether the nonreductive consequences of multiple realizability can be circumvented by scientific theories framed in terms of narrow domain-specific properties, or wide disjunctive properties.

"Post-Structuralist Angst, Critical Notice: John Bickle, Psychoneural Reduction: The New Wave," Philosophy of Science 68, no.3 (2001): 377-393. [pdf] John Bickle has written an impressive book, polished with formal techniques applied to various topics in the philosophy of science. Nevertheless, I critically evaluate Bickle’s version of scientific theory reduction. I press three main points. First, a small point, Bickle modifies the new wave account of reduction developed by Paul Churchland and Clifford Hooker by treating theories as set-theoretic structures. But that structuralist gloss seems to lose what was distinctive about the Churchland-Hooker account, namely, that a corrected theory must be specified entirely by terms and concepts drawn from the basic reducing theory. Set-theoretic structures are not terms or concepts but the structures that they describe. Second, and more serious, a familiar problem for classical positivist account of reduction resurfaces within this newest wave of thinking, namely, commitment to property identities and inter-theoretic bridge laws (a problem I discussed at more length in "Collapse of the New Wave"). Indeed, this problem is exacerbated by Bickle’s conciliatory treatment of property plasticity, since he is willing to grant that a large number of special science terms denote multiply realized properties, at least if realistically construed. Still, in the end, Bickle sidesteps the reduction of properties by appealing to Hooker’s "function-to-structure token reduction." This is an interesting move with an intriguing concept of reduction. But problems remain. For, third, Bickle and Hooker's function-to-structure token reduction is actually a guised form of eliminative materialism. But that should be unacceptable since the position extends well beyond any modest revisionism for suspect items from a folk theory, say, in folk psychology or folk biology. Instead, it applies to functional terms and concepts employed throughout well-developed and explanatorily successful sciences.

"Collapse of the New Wave," Journal of Philosophy 95, no.2 (1998): 53-72. [pdf] I critically evaluate the influential new wave account of theory reduction in science developed by Paul Churchland and Clifford Hooker. First, I cast doubt on claims that the new wave account enjoys a number of theoretical virtues over its competitors, such as the ability to represent how false theories are reduced by true theories. Second, I argue that the genuinely novel claim that a corrected theory must be specified entirely by terms from the basic reducing theory is in fact too restrictive for scientific practice and should be rejected. Basic theories co-evolve with nonbasic theories in a mutually interactive way, and thus the basic theories incorporate the concepts and concerns of nonbasic theories. Third, I show that once its ontological consequences are duly noted, the reductive part the new wave account collapses into the classical theory developed within the logical empiricist tradition. As such, it still falls prey to standard anti-reductionist argument based upon multiple realizability and the cross-classification of special science and physical science terms.

"Searle, Syntax, and Observer Relativity," Canadian Journal of Philosophy 26 (1996): 101-122. [pdf]. In defense of the computational model of the mind, I critically examine some provocative arguments that John Searle presents in his book The Rediscovery of Mind to support the claim that the syntactic states of a classical computational system are "observer relative" or "mind dependent" or otherwise less than fully and objectively real. I begin by explaining how this claim differs from Searle's earlier and more well-known claim that the physical states of a machine, including the syntactic states, are insufficient to determine its semantics. In contrast, his more recent claim concerns the syntax, in particular, whether a machine actually has symbols to underlie its semantics. I then present and respond to a number of arguments that Searle offers to support this claim, including whether machine symbols are observer relative because the assignment of syntax is arbitrary, or linked to universal realizability, or linked to the sub-personal interpretive acts of a homunculus, or linked to a person's consciousness. I conclude that a realist about the computational model need not be troubled by such arguments. Their key premises need further support.

"Constructival Plasticity," Philosophical Studies 74, no.1 (1994): 51-75. [pdf] Some scientists and philosophers have claimed that there is a converse to multiple realizability. While a given higher-level property can be realized by different lower-level properties (multiple realizability), a given lower-level property can in turn serve to realize different higher-level properties (this converse I dubbed the unfortunately obscure "constructival plasticity" to emphasize the constructive metaphysics involved when realizing properties generate different realized properties in the stated way). I begin by defining multiple realizabilty in a formal way, then turn to the relation in question. By my analysis, for the converse claim to be true, a lower-level property G1 that realizes a higher-level F must be taken in conjunction with some other base condition G2 so that a difference in G2 allows G1 to determine some other higher-level property E but not F (otherwise there would be violations of supervenience). The realization law thus has the form: (G1 & G2) => F. As such, the base property G1 is insufficient by itself to produce F. It is an insufficient but necessary part of a sufficient condition. I also point out that this makes the realization base property an INUS condition, if combined with multiple realizability. Specifically, if F is multiply realized by properties other than the pair G1 and G2, then G1 is an insufficient but necessary part of an unnecessary but sufficient condition.

"Species-Specific Properties and More Narrow Reductive Strategies," Erkenntnis 38 (1993): 303-321. [pdf]. In order to accommodate the phenomenon of multiple realizabiliy, some philosophers have appealed to species-specific properties, and even more narrowly construed individual-at-a-time-relativized properties, rather than more general properties that range over broader domains. The idea, for example, is that while the property of 'having pain' might be multiply realized by different kinds of physical properties, the property of 'having human pain' is not. This paper is an early examination of this narrow reductive strategy (NRS). It focuses more on the metaphysics of properties, pace Kim's version of the NRS, rather than the semantics of multiple referring terms, pace Lewis' version of the NRS (for the latter, see Horgan, "Multiple Reference, Multiple Realization, and the Reduction of Mind," in G. Preyer and F. Siebelt, eds., Reality and Humean Supervenience: Essays on the Philosophy of David Lewis. Landham, MD: Rowman & Littlefield (2001), 205-210). I wrote the paper a few years earlier as a graduate student, and I certainly would write it differently today. But I think it raised some interesting issues, chiefly, whether the NRS might be better viewed as a form of theory replacement rather than reduction, and whether its most narrowly construed 'individual-at-a-time-relative' terms might be better viewed as designating token events (objects having properties at times) rather than types or properties.