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Logical models of argument formalize commonsense reasoning while taking process and computation seriously. This survey discusses the main ideas which characterize different logical models of argument. It presents the formal features of a few main approaches to the modeling of argumentation. We trace the

. Inspired by legal reasoning, this paper presents a formal framework for assessing conflicting arguments. Its use is illustrated with applications to realistic legal examples, and the potential for implementation is discussed. The framework has the form of a logical system for defeasible argumentation. Its language, which is of a logic--programming--like nature, has both weak and explicit negation, and conflicts between arguments are decided with the help of priorities on the rules. An important feature of the system is that these priorities are not fixed, but are themselves defeasibly derived as conclusions within the system. Thus debates on the choice between conflicting arguments can also be modelled. The proof theory of the system is stated in dialectical style, where a proof takes the form of a dialogue between a proponent and an opponent of an argument. An argument is shown to be justified if the proponent can make the opponent run out of moves in whatever way the opponent attac...

We present a formal model of argumentation based on situation calculus which captures both the logical and the procedural aspects of argumentation processes. The logic is used to determine what is accepted by each agent participating in the discussion and by the group as a whole, on the basis of the speech acts performed during argumentation. Argumentation protocols, also called rules of order, describe declaratively which speech acts are legal in a particular state of the argumentation. We first discuss argumentation with fixed rules of order. Our model tolerates protocol violations but makes it possible to object to illegal actions. In realistic settings the rules of order themselves can at any time become the topic of the debate. We show how meta level argumentation of this kind can be modelled in what we call dynamic argument systems. To illustrate the notions introduced in the paper we present a reconstruction of Rescher's theory of formal disputation and a dynamic argument system with three levels which we use to discuss a murder case. 1

. This paper analyses legal reasoning with precedents in the setting of a formally defined dialogue game. After giving a legal-theoretical account of judicial reasoning with precedents, a formal method is proposed for representing precedents and it is discussed how such representations can be used in a formally defined dialectical protocol for dispute. The basic ideas are to represent cases as argument structures (including pro and con arguments, and the arguments for adjudicating their conflicts) and to define certain case-based reasoning moves as strategies for introducing information into a dispute. In particular, analogizing and distinguishing are conceived as elementary theory construction moves, which produce new information on the basis of an existing stock of cases. The approach also offers the possibility of using portions of precedents and of expressing criteria for determining the outcome of precedent-based disputes. The analysis, which is partly based on argument-based sema...

We articulate a dialectical argumentation framework for qualitative representation of epistemic uncertainty in scientific domains. The framework is grounded in specific philosophies of science and theories of rational mutual discourse. We study the formal properties of our framework and provide it with a game theoretic semantics. With this semantics, we examine the relationship between the snaphots of the debate in the framework and the long run position of the debate, and prove a result directly analogous to the standard (Neyman-Pearson) approach to statistical hypothesis testing. We believe this formalism for representating uncertainty has value in domains with only limited knowledge, where experimental evidence is ambiguous or conflicting, or where agreement between different stakeholders on the quantification of uncertainty is difficult to achieve. All three of these conditions are found in assessments of carcinogenic risk for new chemicals.

. This article surveys the use of logic in computational models of legal reasoning, against the background of a four-layered view on legal argument. This view comprises a logical layer (constructing an argument) ; a dialectical layer (comparing and assessing conicting arguments) ; a procedural layer (regulating the process of argumentation); and a strategic, or heuristic layer (arguing persuasively). Each further layer presupposes, and is built around the previous layers. At the rst two layers the information base is xed, while at the third and fourth layer it is constructed dynamically, during a dialogue or dispute. 1

Open multi-agent computational systems are composed of heterogeneous and possibly antagonistic software entities. Characteristic features are limited trust and unpredictable behaviour. Members of such systems may fail to, or even choose not to, conform to the norms governing their interactions. It has been argued that systems of this type should have a formal, declarative, verifiable, and meaningful semantics. We present a theoretical and computational framework being developed for the executable specification of such systems. We adopt an external perspective and view open computational systems as instances of normative systems. In this paper we demonstrate how the framework can be applied to specifying and executing an argumentation protocol based on Brewka’s reconstruction of Rescher’s theory of formal disputation. The specification is formalised in the action language C+ and executed using the ‘Causal Calculator’ (Ccalc) implementation.

Defeasible argumentation is concerned with studying plausible but, at the same time, fallible patterns of reasoning. Because plausible arguments can easily be developed, and not all of them can be in force at the same time, the main thrust of the theory is in deriving sound principles for adjudicating among conflicting lines of argumentation. In this paper, we propose to resolve such conflicts by starting an artificial debate. The explanatory notes will consist of a short introduction to `traditional' defeasible argumentation, followed by a brief exposition of the basic ideas of what is called formal defeasible dialectics here. The paper will be concluded by proving the traditional and dialectic approach to be equivalent. Research area 1985 Mathematics subject classification 68C01; 1987 CR classification scheme F.4.0, I.2.3, - key words and phrases: nonmonotonic reasoning, defeasible dialectics, abstract argumentation system. 1. Introduction This paper attempts to show that a disputa...

This paper describes Hermes, a system that enhances group decision making by providing an argumentation framework to the agents involved. The system organizes the existing knowledge in a discussion graph, which consists of issues, alternatives, positions and preference relations. Argumentation is performed through a set of discourse acts which trigger appropriate procedures for the propagation of information in the graph. Hermes is able to handle incomplete, qualitative and inconsistent information, and provides mechanisms for weighing arguments. Introduction Group Decision Support Systems (GDSSs) have been defined as interactive computer-based systems which facilitate the solution of ill-structured problems by a set of decision makers, working together as a team (Kreamer and King 1988). The main objective of a GDSS is to augment the effectiveness of decision groups through the interactive sharing of information between group members and the computer. This can be achieved by (i) rem...