On Resolving Conflicts Between Arguments

• Published in: Computational intelligence Vol. 16; no. 3; pp. 469 - 497
• Main Author: Roos, Nico
• Format: Journal Article
• Language: English
• Published: Boston, USA and Oxford, UK Blackwell Publishers Inc 01.08.2000
• Subjects: argumentation; defeasible rules; nonmonotonic reasoning
• ISSN: 0824-7935; 1467-8640
• DOI: 10.1111/0824-7935.00120

Argument systems are based on the idea that one can construct arguments for propositions—structured reasons justifying the belief in a proposition. Using defeasible rules, arguments need not be valid in all circumstances, therefore, it might be possible to construct an argument for a proposition as well as its negation. When arguments support conflicting propositions, one of the arguments must be defeated, which raises the question of which (sub‐) arguments can be subject to defeat. In legal argumentation, metarules determine the valid arguments by considering the last defeasible rule of each argument involved in a conflict. Since it is easier to evaluate arguments using their last rules, can a conflict be resolved by considering only the last defeasible rules of the arguments involved? We propose a new argument system where, instead of deriving a defeat relation between arguments, arguments for the defeat of defeasible rules are constructed. This system allows us to determine a set of valid (undefeated) arguments in linear time using an algorithm based on a JTMS, allows conflicts to be resolved using only the last rules of the arguments, allows us to establish a relation with Default Logic, and allows closure properties such as cumulativity to be proved. We propose an extension of the argument system based on a proposal for reasoning by cases in default logic.