This volume presents the refereed proceedings of the 12th International Conference on Deontic Logic and Normative Systems, DEON 2014, held in Ghent, Belgium, in July 2014. The 17 revised papers and the 2 invited papers included in this volume were carefully reviewed and selected from 31 submissions. Topics covered include challenges from natural language for deontic logic; the relationship between deontic and other types of modality: epistemic modality, imperatives, supererogatory, etc.; the deontic paradoxes; the modeling of normative concepts other than obligation and permission, e.g., values; the game-theoretical aspects of deontic reasoning; the emergence of norms; norms from a conversational and pragmatic point of view; and norms and argumentation.

This book collects the papers presented at the 4th International Workshop on Logic, Rationality and Interaction/ (LORI-4), held in October 2013 at the /Center for the Study of Language and Cognition, Zhejiang University, Hangzhou, China. LORI is a series that brings together researchers from a variety of logic-related fields: Game and Decision Theory, Philosophy, Linguistics, Computer Science and AI. This year had a special emphasis on Norms and Argumentation. Out of 42 submissions, 23 full papers and 11 short contributions have been selected through peer-review for inclusion in the workshop program and in this volume. The quality and diversity of these contributions witnesses a lively, fast-growing, and interdisciplinary community working at the intersection of logic and rational interaction.

Judgment aggregation is a mathematical theory of collective decision-making. It concerns the methods whereby individual opinions about logically interconnected issues of interest can, or cannot, be aggregated into one collective stance. Aggregation problems have traditionally been of interest for disciplines like economics and the political sciences, as well as philosophy, where judgment aggregation itself originates from, but have recently captured the attention of disciplines like computer science, artificial intelligence and multi-agent systems. Judgment aggregation has emerged in the last decade as a unifying paradigm for the formalization and understanding of aggregation problems. Still, no comprehensive presentation of the theory is available to date. This Synthesis Lecture aims at filling this gap presenting the key motivations, results, abstractions and techniques underpinning it. Table of Contents: Preface / Acknowledgments / Logic Meets Social Choice Theory / Basic Concepts / Impossibility / Coping with Impossibility / Manipulability / Aggregation Rules / Deliberation / Bibliography / Authors' Biographies / Index