Revising Desires: A possibilistic viewpoint

As extensively studied in the artificial intelligence literature, agents may have to revise their beliefs when they receive a new piece of information, for avoiding inconsistency in their epistemic states, since one cannot believe p and believe ¬p at the same time. Similarly desiring p and ¬p simultaneously does not sound reasonable, since this would amount to be pleased by anything. This motivates an approach for revising desires, a topic remained largely untouched. Desires do not behave as beliefs. While beliefs are closed under conjunction, one may argue that the disjunction of desires reflects the endorsement of each desire. In a possibility theory modeling setting, desires are expressed by a strong possibility set function, while beliefs are encoded by means of a necessity function. The paper outlines an original approach to the revision, the expansion, and the contraction of desires in the framework of possibility theory, and contrasts it with belief revision