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Multiple realization and the commensurability of taxonomies


The past two decades have witnessed a revival of interest in multiple realization and multiply realized kinds. Bechtel and Mundale’s (Philos Sci 66(2):175–207, 1999) illuminating discussion of the subject must no doubt be credited with having generated much of this renewed interest. Among other virtues, their paper expresses what seems to be an important insight about multiple realization: that unless we keep a consistent grain across realized and realizing kinds, claims alleging the multiple realization of psychological kinds are vulnerable to refutation. In this paper I argue that, intuitions notwithstanding, the terms of their recommendation make it impossible to follow, while also misleadingly insinuating that its application virtually guarantees mind-brain identity. Instead of a matching of grains, what multiple realization really requires is a principled method for adjudicating upon differences between tokens. Shapiro’s (J Philos 97(12):635–654, 2000) work on multiple realization can be understood as an attempt to adumbrate just such a method. While his “causal relevance” criterion can easily be mistaken for Bechtel and Mundale’s grain requirement, my analysis reveals exactly where and why these two tests diverge.

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Fig. 1


  1. 1.

    It only appears to be tendentious when a certain paradigm of realization and MR, the so-called “dimensioned” view, has one under its sway (see Gillett 2003).

  2. 2.

    Shapiro ultimately uses his analysis to draw out a dilemma confronting the MR advocate. If a given functional kind is not multiply realized, the traditional argument for its autonomy and irreducibility falls away. If on the other hand the kind is multiply realized, the kind will not be a proper scientific kind, i.e. of the sort that can enter into laws. “Brittleness” might be a multiply realized property, but glass, steel and biscuits are each brittle in their own way: there can be no general science of brittle things. Ranging over such genuinely diverse physical realizations means the kind will not enter into laws (i.e. exhibit lawlike or projectable properties), except for those which are true analytically—such as all mousetraps catch mice, and all eyes see—and this in turn “undercut[s] the traditional motivation for admitting functional kinds into the ontologies of the special sciences” (Shapiro 2000, p. 637). In this paper I will not be addressing this issue, but see Couch (2009a, pp. 262–264) for some criticisms. In more recent work Shapiro himself seems to have backed away from this position (Polger and Shapiro 2016).

  3. 3.

    Bechtel and Mundale’s test at this point can be seen as a bowdlerized version of Shapiro’s causal relevance criterion, which screens off causally irrelevant details when comparing realizing kinds (much as Bechtel and Mundale’s “coarse-graining” procedure does).

  4. 4.

    The nearest they come is this: “When comparing psychological states across different individuals, psychologists...tend to ignore differences and focus on commonalities” (1999, p. 202). If anything, however, one would have thought that this fact should actually discourage kind splitting (see text).

  5. 5.

    In subsequent work, Couch (2009a, b) has been more careful in his remarks, and has brought out explicitly the importance of scientific taxonomy in the individuation of both neural and psychological kinds. Still I notice that in these papers he doesn’t rely on granularity arguments, and indeed is even mildly critical of them (2009b, p. 267). When grains hold sway, MR stands little chance of receiving a fair hearing.

  6. 6.

    By contrast, Couch (2009b, p. 514) puts forward human eyes and pigeon eyes as plausible candidates for MR, and comments: “Accepting that this example is plausible is a revision from an earlier view of mine”.


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This paper was presented to the American Philosophy of Science Association on 3 November 2016, in Atlanta, Georgia. I am particularly indebted to Larry Shapiro and Tom Polger for helpful discussion, as well as three anonymous reviewers. Warm thanks also to Kim Sterelny and Paul E. Griffiths.

Funding This research was supported by an Australian Government Research Training Program (RTP) Scholarship.

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Correspondence to John Zerilli.

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Zerilli, J. Multiple realization and the commensurability of taxonomies. Synthese 196, 3337–3353 (2019).

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  • Multiple realization
  • Bechtel and Mundale
  • Neuroscience
  • Autonomy of psychology
  • Intertheoretic reduction