Anchored narratives and dialectical argumentation

Bart Verheij

Abstract

[1 Modeling legal decision making]

Trying criminal cases is hard. The problem faced by a judge in court can be phrased in a deceptively simple way though, as follows: in order to come to a verdict, a judge has to apply the rules of law to the facts of the case. In a na´ve and often criticized model of legal decision making (reminding of the bouche de la loi view on judges), the verdict is determined by applying the rules of law that match the case facts. This na´ve model of legal decision making can be referred to as the subsumption model.

A problem with the subsumption model is that neither the rules of law nor the case facts are available to the legal decision maker in a sufficiently well-structured form to make the processes of matching and applying a trivial matter. First, there is the problem of determining what the rules of law and the case facts are. Neither the rules nor the facts are presented to the judge in a precise and unambiguous way. A judge has to interpret the available information about the rules of law and the case facts.

Second, even if the rules of law and the case facts would be determined, the processes of matching and applying can be problematic. It can for instance be undetermined whether some case fact falls under a particular rule's condition. Additional classificatory rules are then needed. In general, it can be the case that applying the rules of law leads to conflicting verdicts about the case at hand, or to no verdict at all. In the latter situation, it is to the judge's discretion to fill the gap, in the former, he has to resolve the conflict. In both cases, the judge should provide some further justification of his opinion.

As a result of these difficulties, many consider legal decision making as a kind of gradual theory construction. By selecting and interpreting the available material (legal codes, police reports, court pleadings, etc.), the decision maker constructs a preliminary theory about the applicable rules, the proven facts and the appropriate verdict. He then performs a number of checks on the preliminary theory. Are there no inconsistencies? Is the verdict justified? If necessary, the theory is adapted to solve the weaknesses found.

In several disciplines, models of legal decision making have been designed along these lines of gradual theory construction. E.g., in the psychology of law, Crombag, Van Koppen and Wagenaar have proposed the anchored narratives approach towards the modeling of legal decision making (Dubieuze zaken, 1992, 1994, Anchored narratives, 1993). Their focus is on the psychology of criminal evidence. Legal decisions are seen as structured stories, anchored in common knowledge.

When Crombag, Van Koppen and Wagenaar contrast their theory with logical inference theories, they allude to the possibility of extended logical systems that are better suited as models of legal decision making than the subsumption model (Anchored narratives, p. 22). Especially in the field of artificial intelligence and law, such extended logical systems have indeed been designed (cf., e.g., Hage, 1997, Prakken, 1997, Verheij, Hage and Van Maanen, 1999). Among the topics addressed in such extended legal logics are exceptions, inconsistencies, gaps, contingent validity and rule properties. Below, the focus is on a theory of dialectical argumentation, characterized by the exchange of arguments and counterarguments, as it is being designed during the development of the experimental argument assistance system ArguMed (Verheij, 1999). In the present paper, the anchored narratives and dialectical argumentation approaches are discussed and compared. In section 2, the theory of anchored narratives is summarized, and in the sections 3 and 4 that of dialectical argumentation. The paper ends with a comparison of the two theories in section 5. As an appendix, a formal version of the theory of dialectical argumentation is presented.

[5 Comparison and conclusion]

The theories of anchored narratives and of dialectical argumentation outlined above are closely related in several respects. In both, the problems of exceptions, conflicts and justification are addressed, and a solution is sought for the problem that legal decision making is not a straightforward application of the rules of law to the case facts, but is a gradual process of 'theory construction'.

In the theory of anchored narratives (section 2), these problems are addressed by considering legal decisions as nested stories. If the story of a verdict is problematic, for instance since there is an exception or a conflict, a substory is needed, in which the problem is addressed. Such a substory will have to be more specific in either of two senses: an explanation has to be given for an assumption that was taken for granted in the original story, or a more specific rule is used as an anchor.

In the theory of dialectical argumentation (sections 3 and 4), the focus is on the dialectical arguments that underlie a legal decision. Further argumentation is required if the current dialectical arguments are problematic. It can for instance be necessary that additional supporting or attacking statements are adduced.

There are strong similarities between the two theories. Both adopt a process model of legal decision making. In the theory of anchored narratives, stories are refined by including substories, until a story of sufficient quality and anchoring is found. In the theory of dialectical argumentation, dialectical arguments are constructed, changed or extended, e.g., by making new statements or adducing new reasons and counterarguments. In both theories, some kind of justification can be required in order to show why some conclusion is supported by a reason. The theory of anchored narratives speaks of anchors, the theory of dialectical argumentation of warrants and backings.

In both, exceptions and conflicts are cues to enhance the preliminarily constructed theory about a good decision in the case at hand. In the theory of anchored narratives, exceptions and conflicts are resolved by the use of more specific anchoring rules. For instance, because of the possible unreliability of a witness, the anchoring rule that witnesses are often truthful can be replaced by the rule that witnesses that do not benefit from their own testimony are often truthful. In the theory of dialectical argumentation, exceptions and conflicts give rise to counterarguments. The exception that a witness is unreliable can for instance be adduced as a counterargument by which the testimony by a witness is no longer assumed to be truthful.

There are also differences between the two theories. The first is that the theory of anchored narratives is story-based, while the theory of dialectical argumentation is argument-based. A second difference follows: the theory of anchored narratives is formally less explicit than the theory of dialectical argumentation. Stories are phrased in natural language, while arguments have a formal, logical structure. Third, the theory of anchored narratives is empirically backed by real, dubious cases. On the other hand, the theory of dialectical argumentation is supported by computational models, such as the argument assistance system ArguMed (Verheij, 1999). Finally, the theory of anchored narratives also discusses 'non-logical' elements of legal decision making. For instance, in the discussion of the quality of stories, particular elements of a good story are prescribed, e.g., the issues of the accused's identity, the actus reus, and mens rea. The theory of dialectical argumentation is wholly logical.

In sum, it can be concluded that the theories of anchored narratives and of dialectical argumentation, though arising from different disciplines, viz. legal psychology and artificial intelligence & law, respectively, show an interesting convergence in the problems addressed and the solutions proposed. This suggests at least one topic , viz. the heuristics of legal decision making, in which the two fields can benefit from each other's findings.

Reference:
Verheij, Bart (2001). Anchored narratives and dialectical argumentation. ICAIL-2001 Workshop on AI and Legal Evidence.

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