Abstract

Fuzzy set theory is a mathematical method that allows users to consider concepts that are subject to degree-vagueness between boundaries of full membership and nonmembership. An example might be the idea of development of a nation, the degree of constitutional control in a government, or a person’s understanding of a linguistic number such as “a few” or “certain.” This entry introduces the idea of a fuzzy set as well as the operations on fuzzy sets using examples taken from the literature. It pays particular attention to challenges of interpreting and measurement of membership and between-set comparisons. It concludes with a review of selected applications of fuzzy sets in psychology, political science, and sociology.