Prioritized norms in formal argumentation

in Journal of Logic and Computation (2018)

To resolve conflicts amongst norms, various non-monotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent non-monotonic ... [more ▼]

To resolve conflicts amongst norms, various non-monotonic formalisms can be used to perform prioritized normative reasoning. Meanwhile, formal argumentation provides a way to represent non-monotonic logics. In this paper we propose a representation of prioritized normative reasoning by argumentation. Using hierarchical abstract normative systems (HANS), we define three kinds of prioritized normative reasoning approaches called Greedy, Reduction and Optimization. Then, after formulating an argumentation theory for a HANS, we show that for a totally ordered HANS, Greedy and Reduction can be represented in argumentation by applying the weakest link and the last link principles, respectively, and Optimization can be represented by introducing additional defeats capturing the idea that for each argument that contains a norm not belonging to the maximal obeyable set then this argument should be rejected. [less ▲]

Prioritized Norms and Defaults in Formal Argumentation

in Deontic Logic and Normative Systems (2016) (2016)

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 ... [more ▼]

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. Dung's seminal paper raised the - so far open - challenge of how to use formal argumentation to represent non monotonic logics, highlighting argumentation's value in exchanging, communicating and resolving 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-Eiter's construction in answer set programming can be obtained in argumentation via the weakest and last link principles. We also show how to represent Hansen's recent construction for prioritized normative reasoning by adding arguments using weak contraposition via permissive norms, and their relationship to Caminada's "hang yourself" arguments. [less ▲]