A Multiple Realization Thesis for Natural Kinds

Abstract: Two important thought‐experiments are associated with the work of Hilary Putnam, one designed to establish multiple realizability for mental kinds, the other designed to establish essentialism for natural kinds. Comparing the thought‐experiments with each other reveals that the scenarios in both are structurally analogous to each other, though his intuitions in both are greatly at variance, intuitions that have been simultaneously well received. The intuition in the former implies a thesis that prioritizes pre‐scientific over scientific indicators for identifying mental kinds in certain circumstances, while his intuition in the latter implies a converse thesis, prioritizing scientific over pre‐scientific indicators for identifying natural kinds in analogous circumstances. In this paper I question whether we can consistently endorse both of these intuitions. A consideration is presented to attempt to justify the common intuition found in the multiple realization thought‐experiment. Then it is argued that this same consideration has application in the structurally analogous Twin‐Earth thought‐experiment. This recommends a kind of multiple realization thesis for natural kinds, in opposition to a scientific essentialist approach. The various respects in which mental kinds like pain and natural kinds like water are similar to each other, such that similar philosophical treatments are warranted for both, are enumerated.