Consistency, Rationality and Collective Choice

Though they are related, " consistency " and " rationality " are different concepts. Consistency is concerned with what happens to choices when the set of available alternatives expands or contracts. Rationality is concerned with how the choices are related to a binary relation on the set of all alternatives. In this paper we define a weakened consistency by a strengthening of Sen's ,B condition (Sen [9], [10], [11]). We also define a weakened rationality by two conditions, related to (but different from) Schwartz's rationality conditions [8]. We study the relations between consistency and rationality thus defined, and apply the results to collective choice theory by proving that there exists one and only one Collective Choice Rule that is fully democratic and yields consistent, rational choice functions. Also, the revealed preference relations of these choice functions are transitive.