Reasoning by Cases in Structured Argumentation

We extend the $ASPIC^+$ framework for structured argumentation so as to allow applications of the reasoning by cases inference scheme for defeasible arguments. Given an argument with conclusion `$A$ or $B$', an argument based on $A$ with conclusion $C$, and an argument based on $B$ with conclusion $C$, we allow the construction of an argument with conclusion $C$. We show how our framework leads to different results than other approaches in non-monotonic logic for dealing with disjunctive information, such as disjunctive default theory or approaches based on the OR-rule (which allows to derive a defeasible rule `If ($A$ or $B$) then $C$', given two defeasible rules `If $A$ then $C$' and `If $B$ then $C$'). We raise new questions regarding the subtleties of reasoning defeasibly with disjunctive information, and show that its formalization is more intricate than one would presume.Comment: Proceedings of SAC/KRR 201

A structured argumentation framework for detaching conditional obligations

We present a general formal argumentation system for dealing with the detachment of conditional obligations. Given a set of facts, constraints, and conditional obligations, we answer the question whether an unconditional obligation is detachable by considering reasons for and against its detachment. For the evaluation of arguments in favor of detaching obligations we use a Dung-style argumentation-theoretical semantics. We illustrate the modularity of the general framework by considering some extensions, and we compare the framework to some related approaches from the literature.Comment: This is our submission to DEON 2016, including the technical appendi

Expertise and public policy: a conceptual guide

This paper seeks to provide a guide to better understand: what is expertise, how to determine who are the relevant experts where it comes to the technical aspects of public policy debates, and how to go about choosing between competing expert claims. Executive summary: In developing policy and assessing program effectiveness, policy makers are required to make decisions on complex issues in areas that involve significant public risks. In this context, policy makers are becoming more reliant on the advice of experts and the institution of expertise. Expert knowledge and advice in fields as diverse as science, engineering, the law and economics is required to assist policy makers in their deliberations on complex matters of public policy and to provide them with an authoritative basis for legitimate decision making. However, at the same time that reliance on expertise and the demands made of it are increasing, expert claims have never been subject to greater levels of questioning and criticism. This problem is compounded by the growing public demand that non-experts should be able to participate in debates over issues that impact on their lives. However their capacity to understand and contribute to the technical aspects of these debates may be either limited or non-existent. This paper provides a guide to assessing who is and who is not an expert in the technical aspects of public policy debates, by providing a framework of levels of expertise. It also notes the importance of identifying the specific fields of expertise relevant to the issue in question. The main focus is on scientific and technical areas, but the issues raised also apply in other domains. It then examines the problem of how non-experts can evaluate expert claims in complex, technical domains. The paper argues that, in the absence of the necessary technical expertise, the only way that non-experts are able to appraise expertise and expert claims is through the use of social expertise. This is expertise using everyday social judgements that enables them to determine who to believe when they are not in a position to judge what to believe. In this context, the paper suggests policy makers ask a series of questions: –      can I make sense of the arguments? –      which experts seems the more credible? –      who has the numbers on their side? –      are there any relevant interests or biases? And –      what are the experts’ track records? By identifying the strengths and limitations of each of these strategies, the paper provides guidance on how each might best be used. It also argues that using them in combination improves their strength and reliability. The role of those who can act as intermediaries between technical experts and non-experts is also examined. The paper makes clear that none of these strategies are without problems, but it postulates that a more systematic approach to how non-experts use social expertise might enhance their ability to become active rather than passive consumers of technical expertise

Writing beyond the pale : literature, literary theory, and the law of genre

It has sometimes been claimed that certain texts written by literary theorists defy categorisation. Neither critique nor fiction, and not even identifiable as a hybrid of both, such texts resist efforts to identify their generic affiliation. These texts might have been allowed to stand merely as indicators of their creators' whimsy were it not for the fact that their content and form, not to mention their problematic relationship with what literary theorists profess elsewhere, represent a provocation to literary criticism's established approaches and procedures. This paper reviews one such text, namely Jacques Derrida 's The Post Card, and more particularly the section entitled "Envois", in the light of his essay "The Law of Genre". It asks whether texts like "Envois" repay critical scrutiny which speaks of a-genericity and multi-genericity, and assesses their implications for the future of literature and literary criticism.peer-reviewe

Supporting reasoning with different types of evidence in intelligence analysis

The aim of intelligence analysis is to make sense of information that is often conflicting or incomplete, and to weigh competing hypotheses that may explain a situation. This imposes a high cognitive load on analysts, and there are few automated tools to aid them in their task. In this paper, we present an agent-based tool to help analysts in acquiring, evaluating and interpreting information in collaboration with others. Agents assist analysts in reasoning with different types of evidence to identify what happened and why, what is credible, and how to obtain further evidence. Argumentation schemes lie at the heart of the tool, and sense-making agents assist analysts in structuring evidence and identifying plausible hypotheses. A crowdsourcing agent is used to reason about structured information explicitly obtained from groups of contributors, and provenance is used to assess the credibility of hypotheses based on the origins of the supporting information

Postulates for logic-based argumentation systems

International audienceLogic-based argumentation systems are developed for reasoning with inconsistent information. Starting from a knowledge base encoded in a logical language, they define arguments and attacks between them using the consequence operator associated with the language. Finally, a semantics is used for evaluating the arguments. In this paper, we focus on systems that are based on deductive logics and that use Dung's semantics. We investigate rationality postulates that such systems should satisfy. We define five intuitive postulates: consistency and closure under the consequence operator of the underlying logic of the set of conclusions of arguments of each extension, closure under sub-arguments and exhaustiveness of the extensions, and a free precedence postulate ensuring that the free formulas of the knowledge base (i.e., the ones that are not involved in inconsistency) are conclusions of arguments in every extension. We study the links between the postulates and explore conditions under which they are guaranteed or violated

Classical logic, argument and dialectic

A well studied instantiation of Dung's abstract theory of argumentation yields argumentation-based characterisations of non-monotonic inference over possibly inconsistent sets of classical formulae. This provides for single-agent reasoning in terms of argument and counter-argument, and distributed non-monotonic reasoning in the form of dialogues between computational and/or human agents. However, features of existing formalisations of classical logic argumentation (Cl-Arg) that ensure satisfaction of rationality postulates, preclude applications of Cl-Arg that account for real-world dialectical uses of arguments by resource-bounded agents. This paper formalises dialectical classical logic argumentation that both satisfies these practical desiderata and is provably rational. In contrast to standard approaches to Cl-Arg we: 1) draw an epistemic distinction between an argument's premises accepted as true, and those assumed true for the sake of argument, so formalising the dialectical move whereby arguments\u2019 premises are shown to be inconsistent, and avoiding the foreign commitment problem that arises in dialogical applications; 2) provide an account of Cl-Arg suitable for real-world use by eschewing the need to check that an argument's premises are subset minimal and consistent, and identifying a minimal set of assumptions as to the arguments that must be constructed from a set of formulae in order to ensure that the outcome of evaluation is rational. We then illustrate our approach with a natural deduction proof theory for propositional classical logic that allows measurement of the \u2018depth\u2019 of an argument, such that the construction of depth-bounded arguments is a tractable problem, and each increase in depth naturally equates with an increase in the inferential capabilities of real-world agents. We also provide a resource-bounded argumentative characterisation of non-monotonic inference as defined by Brewka's Preferred Subtheories