Fundamentals of Fuzzy Set Theory

In 1965, L.A. Zadeh published his famous paper “Fuzzy sets” in Information and Control providing a new mathematical tool which enables us to describe and handle vague or ambiguous notions such as “a set of all real numbers which are much greater than 1,” “a set of beautiful women,” or “the set of tall men.” Since then, fuzzy set theory has been rapidly developed by Zadeh himself and numerous researchers, and an increasing number of successful real applications of this theory in a wide variety of unexpected fields has been appearing. The main idea of fuzzy set theory is quite intuitive and natural: Instead of determining the exact boundaries as in an ordinary set, a fuzzy set allows no sharply defined boundaries because of a generalization of a characteristic function to a membership function.