Abstract

This work introduces a system of suppositional argumentation , trying to give a foundation for dealing intuitively with disjunctive information in a defeasible reasoning framework. Defeasible argumentation systems proposed in the field of Artificial Intelligence lack in general of such a capability. Our view is that suppositional reasoning is present in defeasible arguments involving disjunctions, just as in reasoning by cases in classical logic. Disjunctive information can express different plausible alternatives which consideration would improve the results of a debate. Here is studied in what extent an argument assuming such plausible alternative can be considered relevant within the given context, and how those alternatives can be compared on basis of their explicative power. In consequence, a debate can be affected in several aspects, among which counter argumentation, defeat and justification have to be considered. Moreover, a comparison among arguments using specificity is adopted, obtaining that also defeasible contrapositive arguments are treated intuitively. Interesting properties of the system are proved, and common sense rationality is tested with several benchmark problems