The Distinction between Psychological Kinds and Natural Kinds Revisited: Can Updated Natural-Kind Theory Help Clinical Psychological Science and beyond Meet Psychology's Philosophical Challenges?

Philosophers and psychologists have long held that mind-dependent/human (or social) kinds are not natural kinds. Yet in the last three decades philosopher of science Richard Boyd has challenged this belief to widespread acclaim in the philosophy of biology, where the natural-kind status of species taxa has been debated. Boyd proposed that natural-kind status hinges not on a kind's mind independence or on demonstration of its essential properties but rather on whether it supports inductive generalization, in which case it is a “homeostatic property cluster” (HPC) kind. Boyd indicates that any human/mental kind can in principle be a natural kind, without physical reduction of its properties, as long as it constitutes an HPC kind and so can be studied by way of the causal mechanisms that, he theorizes, underlie all natural kinds. In the last decade Boyd's HPC theory of natural kinds has influenced theory of mental disorder kinds and shares commonality with Denny Borsboom's burgeoning “symptom network” approach to psychiatric diagnosis. It therefore warrants more thoroughgoing theoretical and empirical analysis. This article revisits the heterogeneity that inheres in DSM categories and motivated alternative approaches, such as the Research Domain Criteria (RDoC) of the NIMH. Also assessed are two worries about the future of “HPC kinds” of mental disorder kinds: (a) ontological relativism and reification, and (b) epistemic perspectivalism and relativistic knowledge. Though focused on clinical kinds, this analysis has implications for psychological science beyond its clinical subdiscipline.