In the philosophy of mind, multiple realizability, a defined by Jaegwon Kim, is the thesis that mental states are such that they are instantiated in a range of organisms with “widely diverse neural-biological structures” (1). Because a single mental state can be “realized” by organisms with vastly different physiologies, multiple realizability is often claimed to be a threat to typephysicalist theories which reduce the mental to the physical.
In “Multiple Realization and the Metaphysics of Reduction,” Kim argues not against the thesis of multiple realizability itself, but rather against the common view that it effectively disproves reductionist physicalism and, as a result, proves that special sciences like psychology are autonomous (3-4). This paper will examine the disagreement between Kim and Fodor as it pertains in particular to disjunctive properties. It will be argued that Fodor correctly distinguishes between disjunctive properties and multiply realizable properties and that Kim’s analogy between jade and pain is erroneous.
As a result, Fodor’s position that multiple realizability supports the status of the special sciences as being independent and autonomous is more plausible than Kim’s. Kim describes the Correlation Thesis as holding that every instance of a specific “psychological kind,” such as pain, will have a particular “physical kind” which correlates with it in every organism which is able to have that particular mental state, in this case pain (4).
In response, supporters of the multiple realizability thesis who are functionalists have clarified that a mental state is a “second-order” physical state, or that the physical state instatiating a single mental state will not be exactly the same among organisms with different physiological systems. For functionalists, then, the Correlation Thesis is limited by the condition that there is just a similar “structure type” amongst the various organisms which are capable of having the same mental state (5).
However, as Kim points out, within a single system there can be multiple ways for a mental state to be realized. As a consequence of this, for a given mental state, pain, there is a disjunction physical states, of which only the presence of one disjunct (physical state) is required for pain (the mental state) to be instatiated. While each physical state that realizes pain will not itself be a disjunction, there is the question of why the disjunction of all the possible instantiating physical states cannot be the correlate of pain rather than a singular physical state (7).
Most advocates of multiple realizability would view this as a threat to the thesis, as the mental state of pain, instead of having multiple physical states lates, would instead have one correlate that is disjunctive. On a reductionist picture, reducing the mental to the physical means that “higher-level” (mental) properties will be reduced to, or identified with, “lower-level” (physical) properties (9). Properties and states (be they mental or physical) are, as Kim explains, referred to as “kinds” of a particular science (natural or special) by Fodor when they are found in that science’s set of laws.
Kim challenges the view that there must be “bridge laws” which traverse across the two types of kinds, mental and physical, in order to connect each kind with its appropriate correlate. He questions why a mental state (or kind) like pain could not be reduced to a correlate which a disjunction of physical states, which would be unappealing to functionalists, like Fodor, who view disjunctive properties as unfit to be kinds which play a role in the laws of a science (10). Kim presents an example to illustrate his challenge, in which it is found that “jade” does not identify one type of mineral (or kind), nd instead it refers to two separate types of minerals: jadeite and nephrite. So the law that “jade is green” which initially existed turns out to be a conjunction of the laws “jadeite is green” and “nephrite is green. ”
The question, then, is whether the initial law that “jade is green” retains its status as a law. Laws are typically thought to be “projectible,” or verifiable through there being observed “positive instances” of their predictions (11). Kim adds to the example the factor that every positive instance of the law “jade is green” has turned out to be, more particularly, an instance of “jadeite is green. Since “jade is green” has only been confirmed by one of its conjuncts, it seems that there ought to be an issue with claiming that it is a wellproven law. Yet, according to Fodor’s notion of a law, all the confirmed observations of jadeite would “satisfy both the antecedent and the consequent” of the general law “jade is green. ”
A confirmation of the law “jade is green” ends up amounting just to the satisfaction of one of the disjuncts of the disjunction: “jadeite is green” or “nephrite is green. Kim thinks this to be “a cheap, and illegitimate, confirmation procedure” (12). The issue, he stresses, is not that confirming instances of “jade is green” will be one of the two disjuncts, but that these instances lack the relevant “similarity” that they ought to bear to one another. That there are positive instances of jadeite being green yet none of nephrite being green appears to be a significant dissimilarity! (13) According to Kim, intuition tells us that “jade” is not a kind, but that jadeite and nephrite are kinds because they have unique chemical compositions (14).
He takes his example of jade to be analogous to the mental state of pain in that for mental states such as pain, there is supposed to be a disjunction of potential physical states which realize them. Since pain will to be realized by a disjunct which is a member of a disjunction of possible physical realizers, it seems that pain also is a non-kind which is unsuitable for (special) scientific laws. Jade is not considered a “kind” which figures in a law because of the heterogeneity of its positive instances. Kim sees no reason why pain should not also cease to be a kind in virtue of its confirming instances also lacking similarity and unity.
Based on the functionalist notion of mental states being “second-order,” pain, as a result, is simply the disjunction of all the physical states which might realize it. The dilemma for Fodor is supposed to be this: either he holds the multiple realizability thesis and accepts that the physical instantiators of mental states are disjunctive, despite disjunctions being considered unacceptable for scientific laws, or he concedes Kim’s argument and abandons the idea of pain being a “kind” suitable for use in a scientific law (15).
If Kim is right, it appears that pain, in addition to all other mental states which are multiply realizable, might end up being inappropriate candidates for scientific laws, which would undermine “Fodor’s contention that its physical irreducibility renders psychology an autonomous special science” (16). Although there might be particular theories about pain for each type of physiology which includes the mental state, there will be no singular, comprehensive theory of pain which applies to all physiologies which contain the mental state of pain.
Just as “jade” is a conjunction of “jadeite” and “nephrite,” the state of “pain” is rather a “conjunction of pain theories” (17). So, psychology is not relegated to the status of “pseudo-science,” but it is severely restricted in there it can only be “local reduction” of mental kinds to physical kinds within a particular system or physiology (19).