We explore a framework for argumentation (based on classical logic) in which an argument is a pair where the first item in the pair is a minimal consistent set of formulae that proves the second item (which is a formula). We provide some basic definitions for arguments, and various kinds of counter-arguments (defeaters). This leads us to the definition of canonical undercuts which we argue are the only defeaters that we need to take into account. We then motivate and formalise the notion of argument trees and argument structures which provide a way of exhaustively collating arguments and counter-arguments. We use argument structures as the basis of our general proposal for argument aggregation.

. This article investigates to what extent protocols for dynamic disputes, i.e., disputes in which the information base can vary at dierent stages, can be justied in terms of logics for defeasible argumentation. First a general framework is formulated for dialectical proof theories for such logics. Then this framework is adapted to serve as a framework for protocols for dynamic disputes, after which soundness and fairness properties are formulated for such protocols relative to dialectical proof theories. It then turns out that certain types of protocols that are perfectly ne with a static information base, are not sound or fair in a dynamic setting. Finally, a natural dynamic protocol is dened for which soundness and fairness can be established. 1. Introduction This paper studies the exchange of arguments and counterarguments in dynamic disputes, i.e., in disputes where the available information can change during the dispute. The research is motivated by two recent developments ...

. This paper presents dialectical proof theories for Dung's preferred semantics of defeasible argumentation. The proof theories have the form of argument games for testing membership of some (credulous reasoning) or all preferred extensions (sceptical reasoning). The credulous proof theory is for the general case, while the sceptical version is for the case where preferred semantics coincides with stable semantics. The development of these argument games is especially motivated by applications of argumentation in automated negotiation, mediation of collective discussion and decision making, and intelligent tutoring. 1 Introduction An important approach to the study of nonmonotonic reasoning is that of logics for defeasible argumentation (for an overview see [25]). Within this approach, a unifying perspective is provided by the work of [9] and [4] (below called the `BDKT framework'). It takes as input a set of arguments ordered by a binary relation of `attack', and it produces...

. This paper proposes a formal framework for argumentative dialogue systems with the possibility of counterargument. The framework allows for claiming, challenging, retracting and conceding propositions. It also allows for exchanging arguments and counterarguments for propositions, by incorporating argument games for nonmonotonic logics. A key element of the framework is a precise denition of the notion of relevance of a move, which enables exible yet well-behaved protocols. 1 Introduction In recent years, dialogue systems for argumentation have received interest in several elds of articial intelligence, such as explanation [2], AI and law [4, 6], discourse generation [5], multi-agent systems [10, 1], and intelligent tutoring [9]. These developments justify a formal study of such dialogue systems; this paper contributes to this study by an attempt to integrate two relevant developments in the elds of argumentation theory and articial intelligence. In argumentation theory...

Defeasible argumentation frameworks have evolved to become a sound setting to formalize commonsense, qualitative reasoning from incomplete and potentially inconsistent knowledge. Defeasible Logic Programming (DeLP) is a defeasible argumentation formalism based on an extension of logic programming.

Possibilistic Defeasible Logic Programming (P-DeLP) is a logic programming language which combines features from argumentation theory and logic programming, incorporating as well the treatment of possibilistic uncertainty and fuzzy knowledge at object-language level. Solving a P-DeLP query...

Abstract. In this paper, we present a decision support system which is built upon an argumentation framework for practical reasoning. A logic language is used as a concrete data structure for holding statements representing knowledge, goals, and decisions. Different priorities are attached to these items, corresponding to the probability of the knowledge, the preferences between goals, and the expected utilities of decisions. These concrete data structures consist of information providing the backbone of arguments. Due to the abductive nature of practical reasoning, arguments are built by reasoning backwards, and possibly by making suppositions over missing information. Moreover, arguments are defined as tree-like structures. In this way, our computer system, implemented in Prolog, suggests some solutions and provides an interactive and intelligible explanation of this choice. 1

In the last years several specialized techniques for improving web search have been developed. Most existing approaches are still limited, mainly due to the absence of qualitative criteria for ranking results and insensitivity to user preferences for guiding the search. At the same time, defeasible argumentation evolved as a successful approach in AI to model commonsense qualitative reasoning with applications in many areas, such as agent theory, knowledge engineering and legal reasoning. This paper presents ArgueNet, a recommender system that classifies search results according to preference criteria declaratively specified by the user. The proposed approach integrates a traditional web search engine with a defeasible argumentation framework.

Numerous argumentation systems have been proposed in the literature. Yet there often appears to be a shortfall between proposed systems and possible applications. In other words, there seems to be a need for further development of proposals for argumentation systems before they can be used widely in decision-support or knowledge management. We believe that this shortfall can be bridged by taking a hybrid approach. Whilst formal foundations are vital, systems that incorporate some of the practical ideas found in some of the informal approaches may make the resulting hybrid systems more useful. In informal approaches, there is often an emphasis on using graphical notation with symbols that relate more closely to the real-world concepts to be modelled. There may also be the incorporation of an argument ontology oriented to the user domain. Furthermore, in informal approaches there can be greater consideration of how users interact with the models, such as allowing users to edit arguments and to weight influences on graphs representing arguments. In this paper, we discuss some of the features of argumentation, review some key formal argumentation systems, identify some of the strengths and weaknesses of these formal proposals, and finally consider some ways to develop formal proposals to give hybrid argumentation systems. To focus our discussions, we will consider some applications, in particular an application in analysing structured news reports.

In spite of the significant evolution of spelling and grammar checkers for word-processing software, the problem of judging the appropriateness of language usage in different contexts remains to a large extent still unsolved. This paper presents a novel, argumentative approach to providing proactive assistance for language usage assessment on the basis of the web linguistic corpus. A defeasible argumentation system determines if a given expression is ultimately acceptable by analyzing a defeasible logic program which encodes the user's preferences. Those expressions assessed as unsuitable are further inspected automatically to help the user make the necessary repairs.