Since Lotfi A. Zadeh published his now classic paper almost fifteen years ago, fuzzy set theory has received more and more attention from researchers in a wide range of scientific areas, especially in the past few years. This theory is attractive because it is based on a very intuitive, although somewhat subtle, idea capable of generating many intellectually appealing results that provide new insights to old, often-debated questions. Opinion is still divided about the importance of fuzzy set theory. Some people have argued that many contributions were simply exercises in generalization. However, several significant and original developments have recently been proposed, which should convince those who are still reluctant. Anyway, fuzziness is not a matter of aesthetics; neither is it an ingredient to make up arid formal constructions; it is an unavoidable feature of most humanistic systems and it must be dealt with as such.
