Douglas Walton

(? - 2020)

In this paper, it is shown how formal dialectic can be extended to model multi-agent argumentation in which each participant is an agent. An agent is viewed as a participant in a dialogue who not only has goals, and the capability for actions, but who also has stable characteristics of types that can be relevant to an assessment of some of her arguments used in that dialogue. When agents engage in argumentation in dialogues, each agent has a credibility function that can be adjusted upwards or downwards by certain types of arguments brought forward by the other agent in the dialogue. One type is the argument against the person or argumentum ad hominem, in which personal attack on one party's character is used to attack his argument. Another is the appeal to expert opinion, traditionally associated with the informal fallacy called the argumentum ad verecundiam. In any particular case, an agent will begin a dialogue with a given degree of credibility, and what is here called the credibility function will affect the plausibility of the arguments put forward by that agent. In this paper, an agent is shown to have specific character traits that are vital to properly judging how this credibility function should affect the plausibility of her arguments, including veracity, prudence, sincerity and openness to opposed arguments. When one of these traits is a relevant basis for an adjustment in a credibility function, there is a shift to a subdialogue in which the argumentation in the case is re-evaluated. In such a case, it is shown how the outcome can legitimately be a reduction in the credibility rating of the arguer who was attacked. Then it is shown how the credibility function should be brought into an argument evaluation in the case, yielding the outcome that the argument is assigned a lower plausibility value.

IT is strange that the informal fallacies should strike us as such obvious breaches of thinking and advocacy, yet should have met with such little success in finding a respectable home within mature logical theory. It might seem that respectable and mature logical theory is most mature and most respectable in the theory of propositions, and that its maturity and respectability in the other logical domains rapidly diminish in inverse proportion to the susceptibility of those domains to be reduced to the logic of propositions. But we are not anxious to promote so severe a view of theoretical accomplishment, and we shall suppose that, at the very least, the informal fallacies have a degree of systematicity that will at once advance our understanding of them nicely beyond the level of intuitive impressions, and also place into retirement the hopelessly inadequate accounts that litter too many otherwise admirable textbooks.

Wigmore thought that there was a science of proof underlying legal reasoning that could be displayed in any given case as a graphic sequence of argumentation from the evidence in the case leading to the ultimate probandum. Argumentation technology has now vindicated this approach by providing useful qualitative methods that can be applied to identifying, analyzing, and evaluating the pro and con arguments put forward by both sides in a trial. In this chapter, it is shown how to apply argumentation schemes, such as argument from witness testimony, using argument diagrams applied to typical sequences of evidence-based legal reasoning in which there is a successive refinement of arguments displayed as the evidence comes into a case. It is shown how argument from applying rules to cases, teleological, argument from expert witness testimony, and abductive reasoning are centrally important for this purpose.

This paper presents a formalization of informal logic using the Carneades Argumentation System, a formal, computational model of argument that consists of a formal model of argument graphs and audiences. Conflicts between pro and con arguments are resolved using proof standards, such as preponderance of the evidence. Carneades also formalizes argumentation schemes. Schemes can be used to check whether a given argument instantiates the types of argument deemed normatively appropriate for the type of dialogue.

This paper analyzes selected examples of uses of argumentation tactics that exploit emotive language, many of them criticized as deceptive and even fallacious by classical and recent sources, including current informal logic textbooks. The analysis is based on six argumentation schemes, and an account of the dialectical setting in which these schemes are used. The three conclusions are (1) that such uses of emotive language are often reasonable and necessary in argumentation based on values, (2) but that they are defeasible, and hence need to be seen as open to critical questioning (3) and that when they are used fallaciously, it is because they interfere with critical questioning or conceal the need for it. The analysis furnishes criteria for distinguishing between arguments based on the use of emotive words that are reasonable tools of persuasion, and those that are fallacious tactics used to conceal and distort information.

A problem for dialogue models of argumentation is to specify a set of conditions under which an opponent’s claims, offered in support of a standpoint under dispute, ought to be challenged. This project is related to the issue of providing a set of acceptability conditions for claims made in a dialogue. In this paper, we consider the conditions of suspicion and trust articulated by Jacobs (Alta, 2003), arguing that neither are acceptable as general conditions for challenge. We propose a third condition that attempts to mark a middle ground between suspicion and trust.

There are emotively powerful words that can modify our judgment, arouse our emotions and influence our decisions. This paper shows how the use of emotive meaning in argumentation can be explained by showing how their logical dimension, which can be analysed using argumentation schemes, combines with heuristic processes triggered by emotions. Arguing with emotive words is shown to use value-based practical reasoning grounded on hierarchies of values and maxims of experience for evaluative classification.

This paper shows how the critical questions matching an argumentation scheme can be mod-eled in the Carneades argumentation system as three kinds of premises. Ordinary premises hold only if they are supported by sufficient arguments. Assumptions hold, by default, until they have been questioned. With exceptions the negation holds, by default, until the exception has been supported by sufficient arguments. By “sufficient arguments”, we mean arguments sufficient to satisfy the applicable proof standard.

Knowledge plays an important role in argumentation. Yet, recent work shows that standard conceptions of knowledge in epistemology may not be entirely suitable for argumentation. This paper explores the role of knowledge in argumentation, and proposes a notion of knowledge that promises to be more suitable for argumentation by taking account of: its dynamic nature, the defeasibility of our commitments, and the non-monotonicity of many of the inferences we use in everyday reasoning and argumentation

If one looks to the current textbook lore for reliable taxonomic and analytical information about the petitio principii, one is met with conceptual disarray and much too much nonsense. The present writers have recently attempted to furnish the beginnings of a theoretical reconstruction of this fallacy which is at once faithful to its formidable complexity yet useful as guide for its detection and avoidance. The fact is that the petitio has had a lengthy and interesting history, and in this paper we shall want to explore certain features of its development, such as it may have been. The principal origins of the concept of circular argument are to be found in Aristotle. The Aristotelian doctrine recurs with variations in the sophismata literature of the middle ages and in logic texts and manuals right up to the present day.

This paper outlines a three-part analysis of the traditional informal fallacy of ad ignorantiam. As initially characterized, the fallacy consists in arguing that failure to prove falsity (truth) implies the truth (falsity) of a proposition. First, the fallacy is located within confirmation theory as a confusion between the categories of "lack of confirming evidence" and "presence of disconfirming evidence". Second, the structure of the fallacy can be seen as an illicit negation shift in Hintikka-style epistemic logic. Third, the fallacy can be studied as an attempt to unfairly shift the burden of proof in a dialectical game. We suggest that research on ad ignorantiam needs a broadening of the scope of philosophical logic to encompass concepts of correct argument in these three contexts.

We provide a retrospective of 25 years of the International Conference on AI and Law, which was first held in 1987. Fifty papers have been selected from the thirteen conferences and each of them is described in a short subsection individually written by one of the 24 authors. These subsections attempt to place the paper discussed in the context of the development of AI and Law, while often offering some personal reactions and reflections. As a whole, the subsections build into a history of the last quarter century of the field, and provide some insights into where it has come from, where it is now, and where it might go.