Evaluating Argumentation Semantics with Respect to Skepticism Adequacy

Analyzing argumentation semantics with respect to the notion of skepticism is an important issue for developing general and wellfounded comparisons among existing approaches. In this paper, we show that the notion of skepticism plays also a significant role in order to better understand the behavior of a specific semantics in different situations. Building on an articulated classification of argument justification states into seven distinct classes and on the definition of a weak and a strong version of skepticism relation, we define the property of skepticism adequacy of an argumentation semantics, which basically consists in requiring a lesser commitment when transforming a unidirectional attack into a mutual one. We then verify the skepticism adequacy of some literature proposals and obtain the rather surprising result that some semantics fail to satisfy this basic property.