Argumentation and Theory of Evidence

The purpose of this paper is to present some new methods widely in use in argumentation theory and informal logic that have applications to the theory of evidence in law. In recent years, a new pragma-dialectical approach1 to argumentation, along with developments in the analysis of logical fallacies2 and dialogue logic,3 has forged these methods together into a single new approach to the evaluation of arguments. This new approach expands the traditional focus of logic on deductive and inductive arguments. It enables a critic to evaluate an argument with respect to how it was used for some communicative purpose in a given case. Research efforts by legal scholars have already been made to applying this new approach to legal argumentation and evidence4 a In this paper, a general overview is given to show how the new methods are applicable to evidence theory in law. In addition to being a survey, the article also presents a new view of some key notions vital to the legal logic of evidence. The two key notions that are most central are those of relevance and probative weight. The notions can be modeled in a new way (or in a way that seems new to many) by introducing a dialogue-based theory of argumentation in which inferences of different kinds are chained together to aim at proving an ultimate conclusion of the dialogue. These notions were already prominent in Wigmore's theory of evidence,5 and the roots of them trace back though Locke and Bentham6 to the ancient notion of plausibility in Greek philosophy. But they seem new because they have been ignored for a long time in mainstream logic, and because only now have they been put together in such a way that they can be modeled in a formal structure. Many of Wigmore's ideas, like 'evidence charts' and `probative weight', that formerly seemed obscure, form a logical point of view, are shown to have a precise logical structure. They show the way to developing new methods for the analysis -and evaluation of legal argumentation. Prominent in the new approach is the technique of argument diagramming. Wigmore is shown to have been an important precursor of modem informal logic through his pioneering use of argument diagramming as applied to case studies of legal evidence.