Ideals, central tendency, and frequency of instantiation as determinants of graded structure in categories.

Three possible determinants of graded structure (typicality) were observed in common taxonomic categories and goal-derived categories: (1) an exemplars similarity to ideals associated with goals its category serves; (2) an exemplars similarity to the central tendency of its category (family resemblance); and (3) an exemplars frequency of instantiation (peoples subjective estimates of how often it is encountered as a category member). Experiment 1 found that central tendency did not predict graded structure in goal-derived categories, although it did predict graded structure in common taxonomic categories. Ideals and frequency of instantiation predicted graded structure in both category types to sizeable and equal extents. A fourth possible determinant—familiarity—did not predict typicality in either common taxonomic or goal-derived categories. Experiment 2 demonstrated that both central tendency and ideals causally determine graded structure, and work showing that frequency causally determines graded structure is discussed. Experiment 2 also demonstrated that the determinants of a particular categorys graded structure can change with context. Whereas ideals may determine a categorys graded structure