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An Introductory Course to Judgment Aggregation

Reaching some form of consensus is often necessary for autonomous agents that want to coordinate their actions or otherwise engage in joint activities. One way to reach a consensus is by aggregating individual information, such as decisions, beliefs, preferences and constraints. Judgment aggregation is a social choice method, which generalises voting, that studies the aggregation of individual judgments regarding the truth-value of logically related propositions. As such, judgment aggregation is applicable for consensus reaching problems in multi agent systems. As other social choice theory, judgment aggregation research is abundant with impossibility results. However, the aim of this tutorial is to give an introduction to the methods of judgment aggregation, not the impossibility results. In particular, the tutorial will introduce the basic frameworks that model judgment aggregation problems and give an overview of the judgment aggregation functions so far developed as well as their social theoretic and computational complexity properties. The focus of the tutorial are consensus reaching problems in multi agent systems that can be modelled as judgment aggregation problems. The desirable properties of a judgment aggregation method applied to these problems are not necessarily the same as properties desirable in legal or political contexts, which is considered to be the native domain of judgment aggregation. After this tutorial the participants are expected to be able to read and understand judgment aggregation literature and have a grasp on the state-of-the-art and open questions in judgment aggregation research of interest to multi agent systems.