In a multi-agent environment, where self-motivated agents try to pursue their own goals, cooperation cannot be taken for granted. Cooperation must be planned for and achieved through communication and negotiation. We present a logical model of the mental states of the agents based on a representation of their beliefs, desires, intentions, and goals. We present argumentation as an iterative process emerging from exchanges among agents to persuade each other and bring about a change in intentions. We look at argumentation as a mechanism for achieving cooperation and agreements. Using categories identified from human multi-agent negotiation, we demonstrate how the logic can be used to specify argument formulation and evaluation. We also illustrate how the developed logic can be used to describe different types of agents. Furthermore, we present a general Automated Negotiation Agent which we implemented, based on the logical model. Using this system, a user can analyze and explore differe...

. Inspired by legal reasoning, this paper presents a semantics and proof theory of a system for defeasible argumentation. Arguments are expressed in a logic-programming language with both weak and strong negation. 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 semantics of the system is given with a fixpoint definition, while its proof theory 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 attacks. KEYWORDS: Argumentation, Nonmonotonic reasoning, Extended logic programming, Legal reasoning, Defeasible priorities Introduction W...

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. 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...

. 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...

. Inspired by legal reasoning, this paper presents an argument-- based system for defeasible reasoning, with a logic--programming--like language, and based on Dung's argumentation--theoretic approach to the semantics of logic programming. The language of the system has both weak and explicit negation, and conflicts between arguments are decided with the help of priorities on the rules. These priorities are not fixed, but are themselves defeasibly derived as conclusions within the system. 1 Introduction This paper presents an argument--based system for defeasible reasoning, with a logic--programming--like language. Argument--based systems analyze defeasible reasoning in terms of the interactions between arguments for alternative conclusions. Defeasibility arises from the fact that arguments can be defeated by stronger counterarguments. Argumentation has proved to be a fruitful paradigm for formalising defeasible reasoning (cf. [13, 17, 18]). Not only does the notion of an argument natu...

. 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

This paper investigates the relation between declarative and procedural accounts of adversarial legal argument. A three- leveled model is proposed, where a formal argumentation framework is built around a logical system and itself embedded in a dialectical protocol for dispute, in such a way that, each time a party adds or retracts information, the argumentation framework reassesses the resulting state of the dispute. The proposed link between the first, logical level and an argumentation framework obviates the need for nonmonotonic logics at the first level, while the proposed link between declarative and procedural models of argumentation enables us to regard induction and analogy not as forms of inference but as heuristics for introducing premises. 1 Introduction With respect to normative models of legal argument, early criticism in AI and Law of e.g. [16] Supported by a Research Fellowship of the Royal Netherlands Academy of Arts and Sciences, and by Esprit WG 8319 `Modelage'. ...

IACAS is a program written to do interactive argumentation on a computer. It allows you to start a dispute, given a number of facts, rules and cases. What is new with IACAS is that it uses the right combinatorics, and, more importantly, incorporates Chisholm's epistemological framework to interpret the outcome of the process. The program is written in LISP and is originally meant to demonstrate the theory outlined in my formal papers on defeasible argumentation. 1. Introduction IACAS is a program written to do interactive argumentation on a computer. 1 It allows you to start a dispute, given a number of facts, rules and cases. The program is written in LISP and is originally meant to demonstrate the theory outlined in my formal papers on defeasible argumentation (Vreeswijk, 1993). IACAS is by no means the only program to do argumentation. Nute (1988), Simari (1989), Pollock (1992), Loui, Olson, Normann, and Merrill (1993) have written similar programs. Nute's program d-PROLOG, for...

Abstract. An implemented context-based reasoning system called ATT-Meta is sketched. The system can perform both reasoning about beliefs of agents and metaphor-based reasoning. In particular, it can perform metaphor-based reasoning about beliefs and reasoning acts. The metaphor-based reasoning and belief reasoning facilities are fully integrated into a general framework for uncertain reasoning. This framework allows for uncertain reasoning and conflict resolution within individual contexts, uncertainty in individual inter-context bridging rules, conflict resolution between the effects of different bridging rules, and conflictresolution across context boundaries when argumentation inside a context conflicts with argumentation outside. 1