ABSTRACT
Possibility theory was coined by L A Zadeh in the late 1970s as an approach to model flexible restrictions constructed from vague pieces of information, described by means of fuzzy sets. Possibility theory is a nonclassical theory of uncertainty, different from probability theory. This brief introduction discusses the basic elements of the theory: possibility and necessity measures (as well as two other set functions associated with a possibility distribution), the minimum-specificity principle which underlies the whole theory, the relations to and differences from the other uncertainty frameworks, and the combination, projection, and conditioning of possibility distributions, as well as the evaluation of fuzzy events.
