Current theories of rules in category learning define rules as one-dimensional boundaries. However, recent evidence suggests that rules may also be two-dimensional boundaries. Four experiments are presented that test for two-dimensional rule use in categories with stimuli composed of integral or separable and commensurate or noncommensurate dimensions. Participant categorization behaviors were organized into groups based upon displayed strategies. These groups were modeled by three models of category learning, ALCOVE, ATRIUM, and a version of ATRIUM modified to use two-dimensional rules. Evidence was found supporting two-dimensional rule use in categories containing stimuliwith commensurate dimensions
