Category grading and taxonomic relations: a mug is a sort of a cup

Gradations in the membership of objects in categories were elicited through hedged question frames (for example, is this “more or less a cup?”; is this “primarily a cup?”). These data are compared with relationships among categories elicited in a standard taxonomic interview (for example, “what are the different types of cups?”). Fuzzy set theory, which formalizes the idea of gradations in set membership, is used to relate category gradations to taxonomic structure. In certain cases, the definitions of fuzzy set theory do not correctly describe informant identifications of objects and require revision. With the necessary extensions, fuzzy set theory offers a means of capturing many aspects of folk classification that cannot otherwise be formally expressed.