A Purely Defeasible Argumentation Framework

Argumentation theory is concerned with the way that intelligent agents discuss whether some statement holds. It is a claim-based theory that is widely used in many areas, such as law, linguistics and computer science. In the past few years, formal argumentation frameworks have been heavily studied and applications have been proposed in fields such as natural language processing, the semantic web and multi-agent systems. Studying argumentation provides results which help in developing tools and applications in these areas. Argumentation is interesting as a logic-based approach to deal with inconsistent information. Arguments are constructed using a process like logical inference, with inconsistencies giving rise to conflicts between arguments. These conflicts can then be handled by well-founded means, giving a consistent set of well-justified arguments and conclusions. Dung\u27s seminal work tells us how to handle the conflicts between arguments. However, it says nothing about the structure of arguments, or how to construct arguments and attack relationships from a knowledge base. ASPIC+ is one of the most widely used systems for structured arguments. However, there are some limitations on ASPIC+ if it is to satisfy widely accepted standards of rationality. Since most of these limitations are due to the use of strict rules, it is worth considering using a purely defeasible subset of ASPIC+. The main contribution of this dissertation is the purely defeasible argumentation framework ASPIC+D. There are three research questions related to this topic which are investigated here: (1) Do we lose anything in removing the strict elements? (2) Do purely defeasible version of theories generate the same results as the original theories? (3) What do we gain by removing the strict elements? I show that using ASPIC+D, it is possible, in a well-defined sense, to capture the same information as using ASPIC+ with strict rules. In particular, I prove that under some reasonable assumptions, it is possible to take a well-defined theory in ASPIC+, that is one with a consistent set of conclusions, and translate it into ASPIC+D such that, under the grounded semantics, we obtain the same set of justified conclusions. I also show that, under some additional assumptions, the same is true under any complete-based semantics. Furthermore, I formally characterize the situations in which translating an ASPIC+ theory that is ill-defined into ASPIC+D will lead to the same sets of justified conclusions. In doing this I deal both with ASPIC+ theories that are not closed under transposition and theories that are axiom inconsistent. At last, I analyze the two systems in the context of the non-monotonic axioms. I show that ASPIC+ and ASPIC+D satisfy exactly same axioms under what I call the “argument construction” interpretation and the “justified conclusions” interpretation under the grounded semantics. Furthermore, because of the lack of strict elements, ASPIC+ satisfies more of the non-monotonic axioms than ASPIC+ in the ``justified conclusions\u27\u27 interpretation under the preferred semantic. This means that ASPIC+ and ASPIC+D may not have the same justified conclusions under the preferred semantics

Hume's Legacy: A Cognitive Science Perspective

Hume is an experimental philosopher who attempts to understand why we think, feel, and act as we do. But how should we evaluate the adequacy of his proposals? This chapter examines Hume’s account from the perspective of interdisciplinary work in cognitive science

'No Thanks': a Socio-Semiotic Approach

This contribution argues for a socio-semiotic approach to natural-language communication which focuses on the connectedness between linguistic code and social and sociocultural practice. Section 1 investigates natural language communication with regard to propositional, interpersonal and interactional meaning from both code and inference-model viewpoints. The results of this discussion are accommodated in the redefinition of two of the most important premises of pragmatics, i.e. rationality and intentionality. In section 2, the interdependence of culture, context and communication is analysed in the framework of ethnomethodology, in which the linguistic realization of an utterance and its degree of contextualization are examined with regard to encoding, decoding, inference and implicature. In section 3 the phenomenon of communicative strategy is analysed in a socio-semiotic framework and special attention is given to the speech acts of denial and rejection. Communicative strategies are defined within the framework of preference organization and classified with regard to their preferred and dispreferred modes of linguistic representation and interpretation. In section 4, the results of the investigation of denials and rejections are systematized in the framework of the dialogue act of a plus/minus validity claim, which is based on Habermas' approach to communication (1987) and Halliday's functional interpretation of language (1996). In the conclusion, culture is defined as both a macro and a micro concept, and is created in and through the process of communication. Linguistic code and sociocultural practice are context-dependent by definition: they are anchored to linguistic contexts, which are embedded in sociocultural contexts, which are embedded in social contexts Thus, the macro concept of culture and its context-dependent manifestation as particular cultural values are reflected in particular communicative strategies which are interdependent on the presentation of self in everyday life (Goffman 1971)

When is argumentation deductive?

This paper discusses and compares various answers to the question when argumentation is deductive. This includes an answer to the questions when argumentation is defeasible and whether defeasible argumentation is a subclass of deductive argumentation or whether it is a distinct form of argumentation. It is concluded that deductive and defeasible argumentation as conceived by Philosophers like Pollock and Rescher and as formalised in the ASPIC (Formula presented.)  framework and systems like Defeasible Logic Programming, are semantically different categories. For this reason, purely syntactic base logic approaches to formal argumentation are unsuitable for characterising this distinction

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

Value and utility in a historical perspective

Since value and utility are the highest profile abstractions that underlie an epoch’s intellectual climate and ethical principles, their evolution reflects the transformation of socioeconomic conditions and institutions. The “Classical Phase” flourished during the first global system, laissez-faire/metal money/zero multilateralism (GS1); the second, “Subjective/Utilitarian” phase marked the long transition to the current epoch of “Modern Subjectivism/General Equilibrium,” tied to the second and extant global system, mixed economy/minimum reserve banking/weak multilateralism (GS2). History has witnessed the material de-essentialization of value and substantialization of utility. But now the two concepts face a thorough transvaluation as the world’s combined demographic and economic expansion encounters ecological/physical limitations. An extended macrohistoric implosion may lead to a third form of global self-organization: two-level economy/maximum bank reserve money/strong multilateralism (GS3). If history unfolds along the suggested path, not only economics, but also thinking about economics would change. It would be considered an evolving hermeneutic of the human condition expressed through global-system-specific texts. The implied critical alteration, with the recognition of the entropy law’s importance as its focal point, matches the prediction of Swiss thinker Jean Gebser (1905-1973) about the impending mutation of human consciousness into its integral/arational structure. Such extrapolations form the context in which the fourth historical phase of value and utility is hypothesized, leading to the material re-essentialization of value and de-substantialization of utility

The production of psychological knowledge as communicative interaction

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.While the traditional natural-scientific model of psychology has in recent decades been extensively criticized, the implications of this criticism for the criteria of epistemologically legitimate psychological knowledge have remained unclear. It is suggested that the production of psychological knowledge should be considered in terms of communicative interaction. Two basic modes of communicative interaction - one-directional and two directional - are proposed. Epistemologically legitimate psychological knowledge requires the adoption of the latter mode. Agreement between the investigator and the person(s) whose conduct is investigated is introduced as the pivotal criterion of the validity of psychological propositions. If psychological knowledge is based on the understanding of the meaning of actions, and if meaning may only be ascertained by means of two directional communicative interaction, agreement seems to be both (a) necessary and (b) sufficient criterion of epistemological validity. Three types of counter-arguments to this view are examined: Habermas's notion of universal rationality, Grunbaum's defence of the pistemological status of the unconscious and Smedslund's common sense psychology. None of these pose any serious challenge to the proposition of agreement as criterion of validity. It is concluded that agreement between the investigator and the other participants in an investigation is the basic criterion of validity in psychology. This conclusion requires a reassessment of the notions of objectivity, relativism and intersubjectivity