Type-Identity Theory

Any mental kind which is nomologically possibly instantiated is identical to a physical kind.  

This gives an idea of how to account for reduction statements about individual types. The thesis that mental types reduces to physical types is best constmed in terms of generic statements, and, hence, in terms of generic reduction. This explication accounts for diversity in terms of conceptual diversity. Sections 6.3 and 6.5 argue that this perfectly matches and vindicates a number of points that have been made in the debate on type-identity theory. The next two sections discuss the connection between conceptual and metaphysical issues in type identity theories, relating them to the explication proposed above. 

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The next two chapters apply the core notion and a few derivative notions to reduction debates in the philosophy of mind (Chap. 6) and the philosophy of science (Chap. 7). Type-identity theories, token-identity theories, conceptions of non-reductive physicalism, and the model of functional reduction can easily be reconstructed based on the explication proposed here, sometimes in an improved form (for example, on the view presented here, it becomes immediately clear where the directionality stems from - an aspect that has been ignored in the heat of the... 

Now it is time to show the relevance of the notion and the fruitfulness of the explication. The concept of reduction defined in the previous chapter is key to an understanding of the reduction-debate in the philosophy of mind. Reductive identity-theories, type-identity theories as well as token-identity theories, and models of functional reduction conceive of reduction precisely as described above These theories are supposed to reconcile strong unity with diversity and directionality according to this conception, a reduces to b only ifa = b. 

In the debate on type-identity theory, the topic of conceptual diversity has been touched on several occasions. Smart (1959) discussed a number of possible objections to type-identity theory, which in fact merely attack a strong version of type-identity theory, rather than the version he, and, according to him. Place tried to defend. These alleged counter-arguments roughly run as follows (Smart 1959, 146 ff.) There is no conceptual route from the mental to the physical, and, therefore, the relevant identity-claims are mistaken. lfa = b, then it is conceptually necessary... 

The way Smart s anonymous opponent conceives of the connection between identity statements and conceptual necessity is, to some extent, mimicked by a way of talking according to which kinds or types are more kin to concepts as conceived of here than to non-representational entities. The idea that there is a conceptual connection between the mental and the physical is tied to a fa on de parler that can be found in various parts of the debate on reductionism and type-identity theory, according to which we can analyze kinds, events or states in functional terms (cf. Block 1995 Kim 2005, 167 Jackson 2005). Type-identity theorists hold that mental types or kinds or properties are identical to physical types or kinds or properties. This suggests that mental kinds and physical kinds are non-representational objects - an interpretation that seems rather plausible given that type-identity theory is a metaphysical theory. Necessarily, there are no conceptual connections between kinds (or non-representational worldly entities), just because kinds are not the right sort of entities to instantiate conceptual relations in any nonderivative way. Kinds are the subject of ontological claims about mental properties. 

Now, type identity theories have been extensively criticized. Physicalists opposed to type-identity theory usually conceive of themselves as non-reducHve physicalists. Interestingly, understanding what non-reductive physicalism consists in requires us to understand what this doctrine is opposed to - namely, reductionism about (mental) types. Moreover, non-reductive physicalists often describe themselves as token-identity theorists, they assume that mental tokens reduce to physical tokens, so that there is strong unity at the token-level. Again, a notion of identity-based reduction is required to hilly understand this idea. The explication offered here cannot only be fruitfully applied in the context of type identity theory. The next section is dedicated to the connection between the explication of reduction and token identity theories. 

In a first approximation, the most prominent kind of argument raised against type identity theory is this Higher-level types can be realized in many different ways. That is There are a number of physical or basic kinds the instances of which... 

This book is not about reductionism and, accordingly, not about the question of whether or not arguments from multiple realizability affect the truth of type-identity theory. However, this book assumes that the concept of reduction is relevant. If the argument from multiple realizability goes through, and if token-identity theories are in some sense non-reductive, then one might wonder whether the concept of reduction is relevant. Let me thus show that token-identity theories employ a notion of reduction similar to the one employed by type-identity theories - a notion that can, again, be defined based on the explication offered above. 

Intuitively, token-identity theory can be described in analogy to type-identity theory For any token of any mental kind, it is identical to a physical token. Note firstly that this version of token-identity theory follows from type-identity theory... 

In the spirit of the adherents of type-identity theory, we would read this statement as follows ... 

Does an explication along these lines, plus a denial of type-identity theory, capture the intuition behind token-identity theory Token identity theorists assume that H2O is more fundamental than water. Even if, on their view, the kind water does not reduce to the kind H2O, there is directionality involved being a water-token is less fundamental than being an H20-token. Similarly, if substance dualism is false then thoughts reduce to brain-processes, what appears to you as the referent of T , when uttered by you, reduces to the spatio-temporal, physical object or chain of events that is you, and your particular mind reduces to the set of particular neural and, maybe, bodily events, just like every other mind reduces to the corresponding neural and bodily substance or chain of events. Thus construed. 

Just as an aside Nominalists should be cautious when embracing token physicaUsm as opposed to type-identity theory. Under a nominalist conception of absiracta, it may, depending on how modal operators enter the formulation of token identity theory, imply type-identity theory for co-extensional properties. 

The notions of type- and token-reduction introduced here bear upon an appropriate understanding of anti-reductionist aspirations in the context of ontological non-reductive physicalism If we assume that there are different, irreducible kinds of properties, but still assume that token- or substance monism is true, then we could use the notion of token-reduction and type-reduction to capture this idea. Non-reductive physicalism, in its ontological version, consists in the affirmation of token-reduction and the denial of type-reduction for the relevant class of tokens and types. The explication proposed above enables us to give an idea of what reductive type- and token-identity theories consist in, and, combing the two, it yields a characterization of non-reductive physicalism. The next sections discuss the application of the explication of reduction to more recent versions of type-identity theory. 

Does multiple realizability really attack type-identity theory It seems obvious that many innocent properties are multiply realizable. For example, a specific mean kinetic energy of an entity can be realized by infinitely many spatial states of the entity s constituents (Kisfler 1999). This does not affect its being a basic kind. Thus, multiple realizability does not seem to threaten identity-theories per se. The trick is to introduce a distinction between heterogeneous multiple realization and homogeneous multiple realization. The former is bad for the identity-theorist,... 

As already mentioned, the argument comes in different forms - some tell the story in counterfactual terms (Lewis 1980), some claim that actually, mental kinds are multiply realized (Kim 1992 Fodor 1974 Block and Fodor 1972 Putnam 1967 Endicott 1993) - and it should be noted that type-identity theory is lost even if there were just one high-level type which is multiply realized, if the argument is sound. 

Up to now, we have reflected upon a family of partly competing and partly complementary theses about the metaphysics of the mind, and on how these theses can be illustrated by reference to the explication of reduction. These theses remain silent about the epistemic or procedural character of reductions (except for the highly implausible idea that the relevant identity-statements express a priori tmths) and about explanatory aspects of reduction. In the philosophy of mind, the dominant view about the link between reduction and explanation is that functional reduction somehow goes together with functional or mechanistic explanation. Functionalism also yields a theory of the metaphysics of mental properties and, contrary to ordinary type-identity theories, it explicitly employs the term reduction . 

The explication proposed in the first part of this book sheds light on conceptions in the philosophy of mind, such as various conceptions of type identity theory, token identity theory and non-reductive physicalism. We thereby motivated the explication - it is not only adequate, but also fruitfiil. 

The two most prominent ontological positions in the philosophy of mind, type-identity theory and token-identity theory, build upon an understanding of reduction that is captured by the job-description that reduction is supposed to reconcile diversity and directionality with strong unity. These theories differ in their interpretation of where to look for unity - on the level of types or on the level of tokens. As such, they do not differ in other respects. Both sorts of theories are underdetermined with respect to directionality and diversity. The explication proposed above fixes these deficiencies. Moreover, it neatly matches the commitments concerning the... 

Jackson, Frank, Robert Pargetter, and Elizabeth Prior. 1982. Functionahsm and type-type identity theories. Philosophical Studies 42 209-225. 

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