Introduction to judgment aggregation

Abstract

The present notes are an improved version of the notes that served as teaching materials for the course Introduction to Judgment Aggregation given at the 23rd European Summer School on Logic, Language and Information (ESSLLI'11, Ljubljana). The notes are structured as follows: Section 1 introduces the field of judgment aggregation, its relations to preference aggregation and some formal preliminaries. Section 2 shows that the paradox that originated judgment aggregation is not a problem limited to propositionwise majority voting but a more general issue, illustrated by an impossibility theorem of judgment aggregation that is here proven. The relaxation of some conditions used in impossibility results in judgment aggregation may lead to escape routes from the impossibility theorems. These escape routes are explored in Section 3. Section 4 presents the issue of manipulation that arises when voters strategically misrepresent their true vote in order to force a different outcome in the aggregation process. Finally, we conclude by sketching a list of on-going research in the field of judgment aggregation (Section 5). © 2012 Springer-Verlag.