Defeasible Arguments Research Articles

Mood and force in defeasible arguments

Argumentation schemes bring artificial intelligence into day to day conversation. Interpreting the force of an utterance, be it an assertion, command, or question, remains a task for achieving this goal. But it is not an easy task. An interpretation of force depends on a speaker’s use of words for a hearer at the moment of utterance. Ascribing force relies on grammatical mood, though not in a straightforward or regular way. We face a dilemma: on one hand, deciding force requires an understanding of the speaker’s words; on the other hand, word meaning may shift given the force in which the words are spoken. A precise theory of how mood and force relate helps us handle this dilemma, which, if met, expands the use of argumentation schemes in language processing. Yet, as our analysis shows, force is an inconstant variable, one that contributes to a scheme’s defeasibility. We propose using critical questions to help us decide the force of utterances.

Endogenous and Dangerous

Empirical studies show that courts frequently cite cases that the parties did not cite during briefing and oral arguments—‘endogenous’ cases. This article shows the cognitive and rational dangers of endogenous cases and presents an empirical study of their use. I contend that judges should avoid using endogenous cases in their reasoning and opinions. This article’s first significant contribution is to provide the first exhaustive treatment in the American legal literature of the rational bases upon which defeasible legal deductions and legal analogies may be built and the critical questions or defeaters that can weaken or bring them down. As far as we know, Aristotle was the first Westerner to formalize logic, about 2,500 years ago. He recognized immediately, however, that the valid deductive forms of reasoning he described do not take us far in reasoning about human affairs. Contemporary law scholars nevertheless talk about rule-based and deductive reasoning as if it exists in the law. But all legal arguments, even apparently deductive ones, are subject to defeat by counterargument—they are ‘defeasible.’ This article shows that legal analogies are in a sense more defeasible, and thus more complex, than legal deductions, and it suggests that legal policy arguments are more defeasible still. But what happens when judges build these arguments around cases that the parties have not cited—endogenous cases? Studies suggest that judges do so about half the time. The theory of defeasible arguments suggests judges should be reluctant to do so, and they should be most reluctant to do so with legal analogies and policy arguments. But until now, no study has examined how judges use endogenous cases. This article’s second significant contribution is an empirical study of cases judges cited in a random sample of federal district court opinions, identifying where they found them and how they used them. It also identifies a hierarchy of badness among endogenous case uses, warning judges away from the most dangerous. It concludes that judges should avoid endogenous cases or, at a minimum, permit the parties to argue the cases before their application. Though the opinions studied here were from federal trial courts, the principles extend to any tribunal that uses opinions from previous cases to guide its decision-making.

A logic of defeasible argumentation: Constructing arguments in justification logic

In the 1980s, Pollock’s work on default reasons started the quest in the AI community for a formal system of defeasible argumentation. The main goal of this paper is to provide a logic of structured defeasible arguments using the language of justification logic. In this logic, we introduce defeasible justification assertions of the type t : F that read as “t is a defeasible reason that justifies F”. Such formulas are then interpreted as arguments and their acceptance semantics is given in analogy to Dung’s abstract argumentation framework semantics. We show that a large subclass of Dung’s frameworks that we call “warranted” frameworks is a special case of our logic in the sense that (1) Dung’s frameworks can be obtained from justification logic-based theories by focusing on a single aspect of attacks among justification logic arguments and (2) Dung’s warranted frameworks always have multiple justification logic instantiations called “realizations”. We first define a new justification logic that relies on operational semantics for default logic. One of the key features that is absent in standard justification logics is the possibility to weigh different epistemic reasons or pieces of evidence that might conflict with one another. To amend this, we develop a semantics for “defeaters”: conflicting reasons forming a basis to doubt the original conclusion or to believe an opposite statement. This enables us to formalize non-monotonic justifications that prompt extension revision already for normal default theories. Then we present our logic as a system for abstract argumentation with structured arguments. The format of conflicting reasons overlaps with the idea of attacks between arguments to the extent that it is possible to define all the standard notions of argumentation framework extensions. Using the definitions of extensions, we establish formal correspondence between Dung’s original argumentation semantics and our operational semantics for default theories. One of the results shows that the notorious attack cycles from abstract argumentation cannot always be realized as justification logic default theories.

Defeasible Legal Argumentation

This paper provides an analysis of defeasible legal reasoning as argumentation. It first gives a general account of the idea of defeasibility and introduces the idea of nonmonotonic reasoning. It then focuses on defeasible argumentation, considering how defeasible arguments can be constructed and how they can be defeated by rebutting and undercutting counterarguments. The dialectical interactions of defeasible arguments are further explored, focusing on reinstatement and reasoning about priorities. The idea of legal systems as the basis for argumentation frameworks is then investigated. The ways in which defeasibility has been understood in legal theory is finally addressed.

Arguments of statutory interpretation and argumentation schemes

Abstract In this paper it is shown how certain defeasible argumentation schemes can be used to represent the logical structure of the most common types of argument used for statutory interpretation both in civil and common law. The method is based on an argumentation structure in which the conclusion, namely, the meaning attributed to a legal source, is modeled as a claim that needs that is be supported by pro and con defeasible arguments. The defeasible nature of each scheme is shown by means of critical questions, which identify the default conditions for the accepting interpretative arguments and provide a method for evaluating a given argument as weak or strong.

Evidential Modals at the Semantic-Argumentative Interface: Appearance Verbs as Indicators of Defeasible Argumentation

This contribution aims at providing an argumentative method to account for epistemic modality and evidentiality. I claim that these two linguistic categories can work as semantic components of defeasible argumentative schemes based on classification processes. This kind of approximate reasoning is, in fact, frequently indicated by appearance verbs which signal that the inferred standpoint is conceived by the speaker as uncertain (epistemic value) due to the deceiving nature of perceptual data (evidential value). Drawing from an analysis at the semantic-argumentative interface, the way in which prototype theory sheds light on the processes of meaning construction underlying defeasible arguments from definition is also shown.

Micropublications: a semantic model for claims, evidence, arguments and annotations in biomedical communications.

BackgroundScientific publications are documentary representations of defeasible arguments, supported by data and repeatable methods. They are the essential mediating artifacts in the ecosystem of scientific communications. The institutional “goal” of science is publishing results. The linear document publication format, dating from 1665, has survived transition to the Web.Intractable publication volumes; the difficulty of verifying evidence; and observed problems in evidence and citation chains suggest a need for a web-friendly and machine-tractable model of scientific publications. This model should support: digital summarization, evidence examination, challenge, verification and remix, and incremental adoption. Such a model must be capable of expressing a broad spectrum of representational complexity, ranging from minimal to maximal forms.ResultsThe micropublications semantic model of scientific argument and evidence provides these features. Micropublications support natural language statements; data; methods and materials specifications; discussion and commentary; challenge and disagreement; as well as allowing many kinds of statement formalization.The minimal form of a micropublication is a statement with its attribution. The maximal form is a statement with its complete supporting argument, consisting of all relevant evidence, interpretations, discussion and challenges brought forward in support of or opposition to it. Micropublications may be formalized and serialized in multiple ways, including in RDF. They may be added to publications as stand-off metadata.An OWL 2 vocabulary for micropublications is available at http://purl.org/mp. A discussion of this vocabulary along with RDF examples from the case studies, appears as OWL Vocabulary and RDF Examples in Additional file 1.ConclusionMicropublications, because they model evidence and allow qualified, nuanced assertions, can play essential roles in the scientific communications ecosystem in places where simpler, formalized and purely statement-based models, such as the nanopublications model, will not be sufficient. At the same time they will add significant value to, and are intentionally compatible with, statement-based formalizations.We suggest that micropublications, generated by useful software tools supporting such activities as writing, editing, reviewing, and discussion, will be of great value in improving the quality and tractability of biomedical communications.

Formalization of the ad hominem argumentation scheme

In this paper, several examples from the literature, and one central new one, are used as case studies of texts of discourse containing an argumentation scheme that has now been widely investigated in literature on argumentation. Argumentation schemes represent common patterns of reasoning used in everyday conversational discourse. The most typical ones represent defeasible arguments based on nonmonotonic reasoning. Each scheme has a matching set of critical questions used to evaluate a particular argument fitting that scheme. The project is to study how to build a formal computational model of this scheme for the circumstantial ad hominem argument using argumentation tools and systems developed in artificial intelligence. It is shown how the formalization built using these tools is applicable to the tasks of identification, analysis and evaluation of the central case studied. One important implication of the work is that it provides a foundational basis for showing how other argumentation schemes can be formalized.

Comment on the Cardozo conference on graphic and visual representations of evidence and inference in legal settings

The paper I presented at the conference gave graphical form to certain kinds of legal arguments: arguments from precedent cases (Loui, 2007). I did not intend to impose a kind of discipline on those who make such arguments. My research aims at elucidating the various forms of reasoning, proposing rules that capture their patterns and regularities, even if those rules and patterns might seem naive to experts at arguing from precedent. To a formalist, a few good rules are better than no rules, especially since artificial intelligence (AI) depends on having rules for computers to follow. A graphical way of diagramming such arguments is simply an alternative way to present the disciplined arguments and to make them comprehensible to humans, especially when the symbols are being manipulated by automata. For some of my logic colleagues, however, the implicit value of such a graphical mechanism is normative: one presumes to improve the quality of legal arguments by imposing a canonical form. This is the presumption that ran badly afoul at this conference. Why should someone who is already very good at making arguments be interested in following our rules for diagramming their arguments? My idea was simply to improve on the ubiquitous ‘Toulmin form’ for diagramming defeasible arguments (Hitchcock and Verheij, 2006). Analogies are a specific kind of argument requiring a specific kind of Toulmin structure. My theory is itself a putative improvement on existing theories of analogy from precedent. Hence, by claiming to have an improved theory of analogical argument, and claiming to refine Toulmin diagrams with that theory, it is easy to imagine that people could be led to better arguments, better rationality and better decision making, by using new diagramming conventions. This is what many formalists and many research computer scientists engaged in logic and visualization would have claimed. But why should it be true? Why are more diagramming rules better than fewer? I did not explicitly claim that people who use our diagrams make better arguments. I would not even have claimed that people who use Toulmin diagrams make better arguments with those diagrams. My paper was actually a ‘Modest Proposal for Annotating the Dialectical State’ and literary tradition required that such a paper be ironic or satirical, even humorous in the face of serious circumstances (Swift, 1996). So I suggested, whimsically, that the boxes and arrows and recursive structure of argument graphs could be replaced by a single historical image: the face of a political candidate, or a civil war general, perhaps even a football quarterback. Throw out all the rigid logical form, I wrote tongue-in-cheek, and use Barack Obama’s face for a new and untested argument of great popular force, or George W. Bush’s face for an old argument that has gotten progressively more difficult to make and which began on dubious grounds anyway. It was not such a bad idea: replace the Microsoft Windows style summaries that use plus and minus signs (or red and green lights) with a richer set of ‘emoticons.’ Some arguments get a plus sign, or a green light, when many

Argumentation support software: boxes-and-arrows and beyond

This paper is about software to support argumentative tasks for lawyers. The focus is on the visualization and evaluation of warranted defeasible arguments. The opportunities provided by ‘boxes-and-arrows’ diagrams of arguments are treated, but the paper also addresses limitations. It is argued that finding natural design, improving usefulness and including content are central research challenges for the field of argumentation support software. It is of highest priority that claims about the extent to which these challenges have been met become better supported by evidence, e.g. by empirical studies.

An Automated System for Argument Invention in Law Using Argumentation and Heuristic Search Procedures*

Abstract. A heuristic search procedure for inventing legal arguments is built on two tools already widely in use in argumentation. Argumentation schemes are forms of argument representing premise-conclusion and inference structures of common types of arguments. Schemes especially useful in law represent defeasible arguments, like argument from expert opinion. Argument diagramming is a visualization tool used to display a chain of connected arguments linked together. One such tool, Araucaria, available free at http://araucaria.computing.dundee.ac.uk/, helps a user display an argument on the computer screen as an inverted tree structure with an ultimate conclusion as the root of the tree. These argumentation tools are applicable to analyzing a mass of evidence in a case at trial, in a manner already known in law using heuristic methods (Schum 1994) and Wigmore diagrams (Wigmore 1931). In this paper it is shown how they can be automated and applied to the task of inventing legal arguments. One important application is to proof construction in trial preparation (Palmer 2003).

Pragma-dialectics and beyond

Pragma-dialectics is dynamic, context-sensitive, and multi-agent; it promises theories of fallacy and argumentative structure. But pragma-dialectic theory and practice are not yet fully in harmony. Key definitions of the theory fall short of explicating the analyses that pragma-dialecticians actually do. Many discussions involve more than two participants with different and mutually incompatible standpoints. Success in such a discussion may be more than success against each opponent. Pragma-dialectics does well at analyzing arguments advanced by one party, directed at another party; it does much less well at analyzing arguments directed at several opponents at once or at convincing an audience. I suggest a strategy of construing fallacies as defeasible arguments relying on reasonable default principles but applying them in circumstances in which they are undercut or overridden.

Are Some Modus Ponens Arguments Deductively Invalid?

This article concerns the structure of defeasible arguments like: 'If Bob has red spots, Bob has the measles; Bob has red spots; therefore Bob has the measles.' The issue is whether such arguments have the form of modus ponens or not. Either way there is a problem. If they don't have the form of modus ponens, the common opinion to the contrary taught in leading logic textbooks is wrong. But if they do have the form of modus ponens, doubts are raised about the conventional dogma that all arguments having the form of modus ponens are deductively valid. By carefully examining arguments on both sides of the issue, reasonable doubts are raised about the view that all arguments having a modus ponens form are valid.

Argument construction and reinstatement in logics for defeasible reasoning

This paper points out some problems with two recent logical systems --- one due to Prakken and Sartor, the other due to Kowalski and Toni --- designedfor the representation of defeasible arguments in general, but with a specialemphasis on legal reasoning.