fuzzy set a set in which membership is a matter of degree. In classical set theory, for every set S and thing x, either x is a member of S or x is not. In fuzzy set theory, things x can be members of sets S to any degree between 0 and 1, inclusive. Degree 1 corresponds to ‘is a member of’ and 0 corresponds to ‘is not’; the intermediate degrees are degrees of vagueness or uncertainty. (Example: Let S be the set of men who are bald at age forty.) L. A. Zadeh developed a logic of fuzzy sets as the basis for a logic of vague predicates. A fuzzy set can be represented mathematically as a function from a given universe into the interval [0, 1]. See also SET THEORY, VAGUENES. D.H.