Pareto最適な撤回可能帰結を軽信的に正当化する実践的議論意味論

抄録

Dungean semantics is known as the most standard argumentation-theoretic semantics that has the ability to evaluate various kinds of nonmonotonic consequences. The fact can be seen as a theoretical basis of adequacy for evaluating consequences of theoretical argumentation, i.e., argument about what to believe, that should be analyzed in terms of truth. It, however, does not give any theoretical basis of adequacy for evaluating consequences of practical argumentation, i.e., argument about what to do, that should be analyzed in terms of goodness. In order to address adequacy for evaluating consequences of practical argumentation formally, we propose practical argumentation semantics defined on practical argumentation frameworks. A practical argumentation framework has a defeat function specifying each agent's defeat relation caused by the agent's subjective desires, aims or values in conflicting arguments. Practical argumentation semantics is constructed on the notion of acceptability, which states that a set of agents accepts an argument if every argument defeating it is defeated by some argument under an agent in the set. We analyze properties of complete, preferred, grounded, and stable extensions defined for each set of agents. The correctness of our theory is shown by the fact that the practical argumentation semantics is a generalization of both Dungean semantics and Pareto optimality, i.e., a fundamental criterion for social welfare. Finally, we stratify practical argumentation frameworks on the basis of the theoretical facts and analyze properties of the frameworks.