Update Monotone Preference Rules

Abstract

Collective decisions are modeled by preference correspondences (rules). In particular, we focus ona new condition: "update monotonicity" for preference rules. Although many so-called impossibilitytheorems for the choice rules are based on -or related to- monotonicity conditions, this appealingcondition is satisfied by several non-trivial preference rules. In fact, in case of pairwise,Pareto optimal, neutral, and consistent rules; the Kemeny-Young rule is singled out by thiscondition. In case of convex valued, Pareto optimal, neutral and replication invariant rules;strong update monotonicity implies that the rule equals the union of preferences which extend allpreference pairs unanimously agreed upon by k agents, where k is related to the number ofalternatives and agents. In both cases, it therewith provides a charaterization of these rules.microeconomics ;