Generations of mathematicians have been dealing with sets or categories with boundaries that are not clearly defined. This state of affairs is clearly applicable to the social sciences, and here Smithson (psychology, The Australian National U.) and Verkullen (quantitative psychology doctoral candidate, U. of Illinois) argue that fuzzy set theory handles vagueness systematically, deal with constructs that have both categorical and dimensional characters, handle certain multivariate relationships and the general linear model through generalizations of set-theoretic operations, have theoretical fidelity and combines set-wise thinking and continuous variables. They cover the theoretical and practical aspects of measuring membership, analyzing internal structure and properties of a fuzzy set, and explain simple and multivariate relations between fuzzy sets. Annotation ©2006 Book News, Inc., Portland, OR (booknews.com)