 It is thus a process of "generating" a classification structure.Conceptual clustering is closely related to fuzzy set theory, in which objects may belong to one or more groups, in varying degrees of fitness.Since the research by Eleanor Rosch and George Lakoff in the 1970s, categorization can also be viewed as the process of grouping things based on prototypes—the idea of necessary and sufficient conditions is almost never met in categories of naturally occurring things.