The Role of Dialectics in Defeasible Argumentation 1

Artificial Intelligence, 1992

We present a mathematical approach to defeasible reasoning based on arguments. This approach integrates the notion of specificity introduced by Poole and the theory of warrant presented by Pollock. The main contribution of this paper is a precise, well-defined system which exhibits correct behavior when applied to the benchmark examples in the literature. It aims for usability rather than novelty. We prove that an order relation can be introduced among equivalence classes of arguments under the equi-specificity relation. We also prove a theorem that ensures the termination of the process of finding the justified facts. Two more lemmas define a reduced search space for checking specificity. In order to implement the theoretical ideas, the language is restricted to Horn clauses for the evidential context. The language used to represent defeasible rules has been restricted in a similar way. The authors intend this work to unify the various existing approaches to argument-based defeasible reasoning.

ECAI, 2000

Defeasible reasoning is a direction in nonmonotonic reasoning that is based on the use of rules that may be defeated by other rules. It is a simple, but often more efficient approach than other nonmonotonic reasoning systems. This paper presents a family of defeasible reasoning formalisms built around Nute's defeasible logic. We describe the motivations of these formalisms and derive some basic properties and interrelationships. We also describe a query answering system that supports these formalisms and is available on the World Wide Web.

1996

During the last decade, defeasible argumentation has proven to be a fruitful formalization for modelling commonsense reasoning. In this respect, the MTDR framework has come to be a fairly standard approach, because of its simplicity and expressive power. Recently, the framework has been enriched through a number of dialectical considerations, resulting in a new ontology, based on Rescher's model of theory formation through dispute.

The capability of drawing defeasible conclusions in presence of partial information is a crucial factor of intelligent behavior. To achieve this capability, human beings resort to a particular kind of knowledge, called default knowledge. The most significant property of default knowledge is that it can be exploited in the reasoning process even if there is only partial information about the satisfaction of the preconditions which allow its application, on condition that there is no reason to believe that such preconditions are not satisfied. If new information becomes available from which the falsity of such preconditions can be deduced, the conclusions derived from the application of default knowledge have to be retracted. This particular form of reasoning, involving the use of default knowledge, may be called defeasible reasoning. In order to build automated reasoning systems including defeasible reasoning capabilities, many extensions of classical logic have been proposed as mode...

Symbolic and Quantitative Approaches to …, 2007

2001

Artificial Intelligence (AI) has long dealt with the issue of finding a suitable formalization for commonsense reasoning. Defeasible argumentation has proven to be a successful approach in many respects, proving to be a confluence point for many alternative logical frameworks. Different formalisms have been developed, most of them sharing the common notions of argument and warrant. In defeasible argumentation, an argument is a tentative (defeasible) proof for reaching a conclusion.

1995

Abstract The goal of this work is to define a system for defeasible argumentation, as an extension of logic programming. Here, we define Defeasible Logic Programs (dlp), and a notion of defeasible inference from a dlp. The characteristics of a dlp allow to represent different flavors of the closed world assumption (CWA) just as program clauses, thus a CWA clause could be presented for some predicates and not for others.

The standard logical approaches to model argumentation forms that involve defeasibility stress either the point on the non monotonic property of the turn-style or introduce a specific conditional (or a combination of the two). In a game-theoretic approach this means that either it is a property of winning strategies or it is about the rules that define a new logical constant (particle rules). In the present paper we will make use of an alternative to the approaches mentioned about available to the dialogical approach. The dialogical approach, as developed in the appendix, distinguishes between The analysis of defeasible reasoning within the dialogical framework should help to build a link between the approaches of default-logic and the argument-based approach initiated by John Pollock [1987], which defines notions like argument, counterargument, attack and defeat, and defines consequence notions in terms of the interaction of arguments for and against certain conclusions.

Journal of Logic and …, 2004

Defeasible reasoning is a simple but efficient rule-based approach to nonmonotonic reasoning. It has powerful implementations and shows promise to be applied in the areas of legal reasoning and the modeling of business rules. This paper establishes significant links between defeasible reasoning and argumentation. In particular, Dung-like argumentation semantics is provided for two key defeasible logics, of which one is ambiguity propagating and the other ambiguity blocking.

The work reported here introduces Defeasible Logic Programming (DeLP), a formalism that combines results of Logic Programming and Defeasible Argumentation. DeLP provides the possibility of representing information in the form of weak rules in a declarative manner, and a defeasible argumentation inference mechanism for warranting the entailed conclusions. In DeLP an argumentation formalism will be used for deciding between contradictory goals. Queries will be supported by arguments that could be defeated by other arguments. A query q will succeed when there is an argument A for q that is warranted, i. e. the argument A that supports q is found undefeated by a warrant procedure that implements a dialectical analysis. The defeasible argumentation basis of DeLP allows to build applications that deal with incomplete and contradictory information in dynamic domains. Thus, the resulting approach is suitable for representing agent's knowledge and for providing an argumentation based reasoning mechanism to agents.