Token Identity Theory

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 

It is noteworthy that the arguments from multiple realizability did not take a purely epistemological form, namely, that the epistemic possibility of multiple reahzability will make it impossible to uncover and describe the chemical, biological or physical kind we have to identify with the mental one, but rather came in a metaphysical shape In virtue of being multiply realized, mental kinds do not belong to the set of lower-level kinds. 

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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. 

So, how does token-identity theory connect to the notion of reduction Even though it is not a very common term in the literature, we sometimes find variants of the expression token reduction (Cartwright 1999, 32 ff., Hooker 1981, part III Bickle 1998, 223 ff.). Consider the following claim to get an idea of how token-identity theory (as intuitively sketched) relates to our paradigm case of reduction ... 

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. 

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... 

There are two other notions in terms of which one may try to provide a criterion for sharing a domain explanation and token-identity. The idea that explanation can do the job comes from the philosophy of science, where it is often said that a new and better theory should explain the successes and failures of its predecessor. The superior theory is expected to make clear why the inferior theory worked in certain cases and why it failed in other cases. One may try to elevate this explanatory relation into a criterion for sharing a domain. So one may say that Aristotelian physics and mechanics intersect because we can account for the successes and failures of Aristotelian physics in terms of mechanics. This solution seems unsuitable for several reasons. One may note that it is theories which explain, not... 

I won t pursue these matters here. The reason is that NRP theorists must reject this combination of type role-functionalism and token physicalism, for they deny that mental event tokens are identical with physical event tokens. Mental event tokens, they hold, are exemplifications of functional properties and are not identical with exemplifications of physical properties that realize the functional properties. Let us see how to spell out their idea using Kim s theory of events. The idea is that functional properties will be constitutive properties of events rather than characterizing properties of events. Thus, let T be a functional property and P be one of its physical realizers. An exemplification of T by x at t will be the event [x, F, t] the property of which the event is an exemplification will be functional property F. If property T is realized on the occasion in question by P, then X will have Fat t in virtue of having Pat t. It follows that x, P, t] occurs and has role R, and indeed x, P, t will realize x, F, t by virtue of [x, P, t] having R But although [x, P, t R, it is nevertheless the case that x, P, t + x, F, t]. The reason is that P F. Thus, if there are functional properties and they are constitutive properties of events, then exemplifications of functional properties are not identical with exemplifications of their physical realizers. 

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