Multiple Realizability, Qualia and Natural Kinds

1. Multiple Realizability, Qualia and Natural Kinds 1) What is a natural kind? 4) The property-level account of MR Multiple realizability has often been taken to be a relation among properties at different levels, whereby a higher-level property is multiply realizable if it can be realized by more than one lower-level property. This has as a consequence (or a presupposition) the ontological position that “the world is ‘layered.’ Reality comprises ‘levels’ of objects, properties, and laws” (Heil 1999, 189). 6) The determinable/determinate account of MR Natural kinds are groups of objects that have some theoretically significant property, or properties, in common. These properties are significant because an object’s membership of a given natural kind determines how that object will behave. Thus, natural kinds can form a system that supports the explanation and prediction of the behaviour of those objects, including inference to counterfactual cases. Common examples of natural kinds include biological species, chemical elements and compounds, and stuffs, such as salt, wool and heat in a gas. A) A mental property is to its physical realizations as a determinable, like redness, is to its determinates, such as scarlet or crimson. B) Determinables are not genuine properties; determinates are properties. Determinable predicates are satisfied by ranges of sufficiently similar properties (determinates). On this model, we can say that the predicate is in pain, though it holds of particular objects at particular times, and does so in virtue of their properties, nevertheless does not itself designate a property. C) This is not a form of anti-realism or anti-naturalism about determinables: the predicate is in pain can still be employed in theoretically fruitful generalizations, even generalizations that would remain invisible at lower levels of abstraction, and can be projectible in a lawlike way where this ceteris paribus lawlikeness is grounded in the similarity of causal powers picked out by the predicate. • 5) A problem for the property-level account (from Heil 1999) • If some higher-level property—pain, say—is realized in a human being by pyramidal cell activity, then it seems that two properties are being tokened at the same time: there is the property of being pca but there is also the distinct property of being a pain. • Why should we suppose that the higher-level property, in each of its tokenings, is distinct from the lower-level property that realizes it on that occasion? Standardly, because we hold that the special sciences are autonomous: they capture laws and generalizations that are not replaceable by those of lower-level sciences. It follows that properties are individuated by their contributions to the causal powers of objects instantiating them: two properties differ iff they feature in different sets of scientific laws. • But this view is untenable. Consider a higher-level property M and three lower-level realizers, N1 N2 and N3: • If M has a subset of the causal powers of N1 then it is unclear what more there is to the object’s possessing M than its possessing N1. If M has a subset of causal powers held in common between N1 N2 and N3 then M is identical with the physical property defined by these causal powers (and so is not multiply realizable). • If M has a superset of the causal powers of N1 then it is mysterious where the additional causal powers come from. • If M has the same set of causal powers as N1 then it is identical with it (and so is not multiply realizable). 2) Why is multiple realizability a problem for natural kindhood? It’s a problem because it seems to show that the similarities among certain ‘manifest’ kinds—such as pain, desiring p, being a flying thing, or being jade—are not supported by underlying, scientifically interesting commonalities. Chemical compounds and biological species are natural kinds in virtue of their underlying, empirically discovered natures (their chemical composition or, perhaps, their shared evolutionary history). It is these natures that underpin inductive generalizations over the members of those kinds. If water had turned out to be one chemical compound in the Pacific, another in the Atlantic, another in the Great Lakes, and so on, then it would not have been a natural kind. In the same way “…there is no single neural kind N that ‘realizes’ pain, across all types of organisms or physical systems; rather, there is a multiplicity of neural-physical kinds, Nh, Nr, Nm, … such that Nh realizes pain in humans, Nr realizes pain in reptiles, Nm realizes pain in Martians, etc.” (Kim 1992, 5). • 7) Results • MR does not provide any additional difficulties for considering phenomenal kinds to be as good candidates for natural kindhood—and hence a sort of scientific respectability—as any other species of ‘high-level property.’ • Phenomenal properties, though multiply realizable, need not be epiphenomenal: tokenings of determinate pains can have causal powers, consistently with there being no one set of causal powers that is definitive of pain. The determinable/determinate account of MR provides a non–ad hoc solution to the causal problem of consciousness. • The kind of similarity that is relevant for phenomenal kinds is phenomenal similarity. Nothing in the determinable/determinate account of MR requires that the similarity between determinates, in virtue of which they are all versions of the same determinable, be causal, even though the identity conditions for properties (determinates) involve causal powers. However it is an interesting question whether the structure of the space of phenomenal similarity must be isomorphic with the structure of the physical similarity-relations: otherwise how are the phenomenal relations to be explained? • It follows from this account of MR that two identical determinate pains must have relevantly the same physical instantiations (since they will be identical in causal powers). So for determinate pains a kind of mind-brain identity theory is entailed, consistently with the facts of multiple realizability. 3) What are qualia? I am treating qualia, not as functional kinds, but as phenomenal kinds, realized by the brain. On this view pain, for example, is best thought of—albeit loosely—as a kind of ‘stuff,’ like heat or salt, whose essential micro-properties explain both its macro-properties and its lawlike relations to other entities. Although on the one hand multiple realizability is prima facie a more pronounced phenomenon for functional properties than for phenomenal ones, on the other the functionalist response to the multiple realizability threat to natural kindhood is not available to us. Dr. Andrew Bailey Philosophy Department University of Guelph Guelph, Ontario N1G 2W1, Canada abailey@uoguelph.ca www.uoguelph.ca/~abailey References Heil, John (1999). “Multiple Realizability,” American Philosophical Quarterly 36. 189–208. Kim, Jaegwon (1992). “Multiple Realizability and the Metaphysics of Reduction,” Philosophy and Phenomenological Research 52. 1–26. Robb, David (1997). “The Properties of Mental Causation,” The Philosophical Quarterly 47. 178–194. Yablo, Stephen (1992). “Mental Causation,” Philosophical Review 101. 245–280.