A Model For Slippery Slope Argument Based On Formal Argumentation System

Argumentation is a cross-disciplinary topic involving multiple subjects such as phi-losophy,cognitive science,logic,linguistics and computer science.As an approach for non-monotonic reasoning,formal argumentation is promising to bridge the gap between human reasoning and machine reasoning.To achieve this goal,a key problem is how to model natural language arguments by formal argumentation.By consulting some relative researches of informal logic,this thesis deeply analyzes a typical defeasible ar-gument-slippery slope argument(SSA),which is commonly used in daily disputation and many kinds of deliberating context.Focusing on SSA,this thesis tries to model nat-ural language arguments by formal argumentation and proposes a formal argumentation theory for SSA.Case studies and analysis show that the formal theory constructed in this thesis can represent the basic form of SSA,while the results of argument evaluation reveal that the conclusions gained by using this argumentation theory are in line with human intuition.This thesis consists of six chapters.The first chapter clarifies the main purpose,the goal and the method of this research.It briefly introduces the history of formal argumentation and the international and domestic recent developments in this field.By analyzing the characteristics of formal argumentation and informal argumentation,this chapter points out the significance of this research.That is,combining the distinctive advantages of these two fields and achieving mutual promotion.The last section of this chapter outlines the structure of this thesis and clarifies the relationship between the chapters.The second chapter introduces the basic concepts of the formal argumentation systems.Firstly,it starts with the abstract argumentation framework,which has been adopted by various argumentation systems as method for arguments evaluation.Then this chapter explicitly introduces a structured argumentation framework-ASPIC+,and compares it with the other structured argumentation systems that adopted different design choices.By comparison,this chapter points out some advantages of ASPIC+,and clarifies why ASPIC+ is chosen as the main theoretical basis in this thesis.The third chapter discusses some limitation of the current formal argumentation system by comparing the different design choices of rebutting in ASPIC+ and ASP IC-.On the one hand,theoretical analysis shows that the restricted rebutting adopted in ASPIC+ can make the results of an argumentation system satisfies the rationality principles for rule-based argumentation systems(rationality postulates);while the un-restricted rebutting adopted in ASPIC-may cause violations of these principles.On the other hand,an empirical research shows that unrestricted rebutting is more in line with human intuition comparing with restricted rebutting,especially in dialectical con-texts.Thus this dilemma reveals that the current argumentation formalisms should be improved and that a better way to combine naturalness and rationality is needed.The fourth chapter is based on the study of argumentation from informal logic's perspective.It summarizes the components,form,reasoning mechanism and evaluation method of SSA.In short,a SSA usually starts with an initial event or action,and get an unacceptable consequence after a sequence of related events or actions,thus draw a conclusion that the initial step should not be taken.Based on the previous chapters,the fifth chapter combines formal argumentation and informal argumentation,constructs an argumentation theory for SSA.Based on this theory,it gives a formal definition of SSA.By analyzing the way a SSA works.this chapter defines a weak transposition for the rules in SSA.In addition,this chapter proposes that,according to the extent of unacceptability of the bad consequences.SSA can be divided into two types,which are non-extreme SSA and extreme SSA.For a non-extreme SSA,respondents can question the unacceptability of its consequences;while for an extreme SSA,respondents cannot do this.According to the critical questions for SSA in Walton's argumentation scheme,this chapter portrays the types of attacks that a SSA may encountered,and tries to evaluate a SSA by using Dung-style argumentation frameworks.During the modeling process,this chapter also considers the limitations of restricted rebutting in dialectical context,and further compares unrestricted rebutting and restricted rebutting.The sixth chapter summarizes this thesis,clarifies the innovations,and points out the shortcomings of this research,as well as what we can do in the future to further improve it.