Nonmonotonic desires- A possibility theory viewpoint

Abstract. If an agent desires that ϕ and desires that ψ, this agent often also de-sires that ϕ and ψ hold at the same time (ϕ∧ψ). However, there are cases where ϕ ∧ ψ may be found less satisfactory for the agent than each of ϕ or ψ alone. This paper is a first attempt at modeling such nonmonotonic desires. The ap-proach is developed in the setting of possibility theory, since it has been recently pointed out that guaranteed (or strong) possibility measures are a good candidate for modeling graded desires. Although nonmonotonic reasoning has been stud-ied extensively for knowledge, and that preferential nonmonotonic consequence relations can be faithfully represented in the possibilistic setting, nonmonotonic desires appear to require a different approach.