"To carve nature at its joints": On the existence of discrete classes in personality.

In principle, units of personality may be of two varieties: dimensional variables, which involve continuously distributed differences in degree, and class variables, which involve discretely distributed differences in kind. There exists, however, a prevailing and rarely questioned assumption that the units of personality are continuous dimensions and an accompanying prejudice against class variables. We examine this prejudice, the arguments that generated it, and those that uphold it. We conclude that these arguments are applicable to class variables as they often have been explicated, in phenetic terms; by contrast, genetically explicated class variables are not vulnerable to these arguments. We propose criteria for conjecturing and present methods for corroborating the existence of class variables in personality. Specifically, we test a class model of a construct whose conceptual status makes it reasonable to evaluate whether or not the differences between individuals represented by this construct constitute discrete classes. Finally, we examine the implications for conceptualizing and investigating the nature and origins of personality. As a psychological concept, personality re-fers to regularities and consistencies in the behavior of individuals and to structures and processes that underlie these regularities and consistencies. Such phenomena, to the extent that they exist, ought to distinguish individuals from other individuals and to render their actions predictable. Typically, in personality theories, these distinguishing features have been treated as comparative individual differ-ences on the assumption that one can mean-The research and preparation of this manuscript were