In The Multiple Realization Book, Larry Shapiro and I argue that the empirical case for multiple realization is much weaker that it is widely thought to be. We first provide a job description for the phenomenon of multiple realization: multiple realization is supposed to undermine identity-based or reductive theories of psychological kinds. Because psychological kinds are multiply realized, identity theories are insufficiently general—they can not explain all of the target phenomena. On that grounds a functionalist or realization theory is to be preferred. And the argument is intended to generalize to most or all of the "special" sciences—the sciences of the non-fundamental.
With this job description in hand, Shapiro and I provide some criteria for multiple realization. We formulate a recipe for determining when a kind of variation in the world counts as an example of multiple realization. The world is Heraclitean—full of variation—but not all examples of variation are examples of multiple realization. We then argue that actual examples of multiple realization are much rarer than philosophers have assumed they would be. And we explain why it is a mistake to think that multiple realization of the mental is possible even in the absence of plentiful actual examples. We argue that our approach is adequately realist and not eliminativist, that it fits well with contemporary accounts of explanation in philosophy of science, that it can account of both mental causation and a plurality of explanations in the cognitive and brain sciences, and that it can provide a framework for peace in the Middle East.
In my first book, Natural Minds, I argued that the mind-brain identity theory is an attractive theoretical option for a theory of the metaphysical nature of minds. My argument involved first clearing out (as I then thought) some nagging philosophical arguments that the identity theory is known to be false—the multiple realization argument, and Kripke's modal argument. I then offered a thorough characterization of the family of functionalist theories that have dominated philosophy and cognitive science in the latter part of the twentieth century and the early years of the new millenium. On the basis of that formulation, I argued that no individual version of the functionalist theories has all of the merits that are attributed to it, and consequently they are not shown to be superior to the identity theory.
Painting from the cover of Natural Minds, "Gathering Light" by Jacob Cooley, North Carolina.