Categorization, treating distinguishable objects or events equivalently, is an inherently pragmatic function, an act of the body, speech, or mind. Its research history reflects successive waves of debate between an abstract, logical, semantics based approach and more pragmatically oriented theories. Each of these periods contains an implicit or explicit philosophical position, characteristic types of experimental research, and implications both for the development of categories in children and for the relation of language to categories. It is argued that future research could reflect the broadened pragmatic perspective that the categories we use are actually forms of life.