This article summarizes six conceptual dimensions that underlie common assumptions about what counts as an adequate category of psychiatric disorder. These dimensions are 1) causalism-descriptivism, 2) essentialism-nominalism, 3) objectivism-evaluativism, 4) internalism-externalism, 5) entities-agents, and 6) categories-continua. Four different versions of the medical model are described and compared with respect to these dimensions. The medical models vary in several ways, but all can be considered "essentialistic." As a counter to the essentialist homogeneity among the medical models, two nominalist analyses of psychiatric classification are reviewed. In order to fill out the space defined by the conceptual dimensions, two alternatives to medical model approaches are also described. After making some suggestions about where DSM-V might best be aligned with respect to the conceptual dimensions, the authors review the distinction between empirical and nonempirical aspects of classification--and argue that nonempirical aspects of classification are legitimate and necessary.