Prioritized Norms and Defaults in Formal Argumentation

Deontic logic sentences define what an agent ought to do when faced with a set of norms. These norms may come into conflict such that a priority ordering over them is necessary to resolve these conflicts. Dungs seminal paper raises the still open challenge to use formal argumentation to represent non monotonic logics, highlight- ing its value to exchange, communicate and resolve possibly conflicting viewpoints in distributed scenarios. In this paper, we propose a formal framework to study various properties of prioritized non monotonic reasoning in formal argumentation, in line with this idea. More precisely, we show how a version of prioritized default logic and Brewka-Eiters construction in answer set programming can be obtained in argumentation via the weakest and last link principles. We also show how to represent Hansens recent construction for prioritized normative reasoning by adding arguments using weak contraposition via permissive norms, and their relationship to Caminadas "hang yourself" arguments.