During the past 15 years, there has been a great deal of interest in categorization. This work has ranged from the early work in how people classify a particular exemplar as a member of a particular category (Rosch, 1975; Smith, Shoben, & Rips, 1974) to more recent concerns about how categories are structured and learned (Armstrong, Gleitman, & Gleitman, 1983; Medin & Wattenmaker, 1987). Medin (1989) provides a useful summary of this work.