Share This Page Legal Argumentation and Evidence
By Douglas N. Walton
INTRODUCTION
The purpose of Legal Argumentation and Evidence is to provide a new method for analyzing the structure of legal reasoning used in arguing a case and evaluating legal argumentation in general. This book is intended to be of interest to those who work in the legal profession, as well as to those who teach law, but it is not a legal treatise. It takes a fresh look at the structure of legal reasoning by exploring current developments in argumentation theory. This new viewpoint is different from the traditional approaches of deductive and inductive logic because it examines legal argumentation contextually. The relevance of an argument, for example, is seen as depending on a conversational framework in which an issue or conoict of opinions is to be resolved. A character-attack argument, called an ad hominem argument in traditional logic, can be judged to be irrelevant in the main argumentation stage of a criminal trial but relevant at its sentencing stage.
In the new model of argumentation presented here, the form of the argument (that is, its so-called argumentation scheme) is merely one factor in judging its worth. How the argument is used in a specioc context of conversation is also crucially important. This view of argumentation as dialectical (or dialogical) is gradually becoming more widely accepted in current research in law and artiocial intelligence. What is provided here are new foundations for this growing and important research initiative and, at the same time, new and promising ways of looking at legal argumentation and evidence that are of wider interest.
This book sets out an abstract normative model of the fair trial as a goaldirected structure that provides a forum for dispute resolution that, in turn, does justice through the provision of due process. According to the model, the trial contains an adversarial dispute. The purpose of the litigants and their attorneys, as their agents, is to win the dispute. But the rules of evidence and other procedural rules contain this struggle, so that relevant arguments on both sides can be tested out. The trier (judge or jury) can use critical thinking to evaluate the strengths and weaknesses of the arguments used on both sides. The kind of fact-onding reasoning used in legal argumentation depends for its evaluation on its use within the goal-directed conversational setting of the trial as a normative structure. This model of the argument as a conversational exchange, known as ‘‘dialectical argumentation,’’ can also be used to throw new light on the kind of reasoning used in statutory interpretation that is important in determining what law is. ‘‘Dialectical’’ is not meant here in the Hegelian or Marxist sense but is used to evoke the dialectical method of question and answer prized by the Greek philosophers, indicating a view of rational argumentation as a conversational exchange.
The central purpose of the book is to provide a new dialectical foundation or logical underpinning for evidence law. Especially with the recent televising of several prominent trials, many people are expressing serious doubts about whether the legal system and legal decisions are based on any kind of standards of rational thinking. One fundamental concern is that evidence law in particular, which is supposed to be the central pillar of good reasoning and fair procedure in the law, is ‘‘adrift.’’ The underlying basis of such concerns is addressed here in a new theory of evidence, a dialectical one that exhibits a kind of roleplaying argumentation structure and bases the outcome of the argument on conclusions drawn from what is reasonably taken to be evidence presented in the case.
The dialectical theory offers an evaluation of legal arguments on a caseby- case basis, relative to the given information at any particular stage in the development of the case. This new theory is radical in at least two important ways. First, it can be brought to bear on legal arguments that, in the past, have been held to be fallacious by logicians, as well as show how, in the legal context of use, such arguments are not fallacious but reasonable. Second, dialectical theory explains the reasonableness of legal arguments in terms of their plausibility, or what used to be called ‘‘probability’’ in an ancient Greek sense. I feel it is beneocial to re-examine this notion of plausibility.
Legal Argumentation and Evidence seeks to vindicate John H. Wigmore’s theory that there is a science of reasoning underlying the law of evidence, upon which the evidence law needs to be based (Wigmore 1913). It does this not only by providing a new logical framework in which Wigmore’s central concepts of evidence can be expressed. It also traces the origins of these concepts back through Locke and Bentham. Central to the new theory are Bentham’s ideas of probative weight and the chaining together of inferences into sequences of argumentation. Also central is Locke’s idea of degrees of assent.
Wigmore’s long-neglected method of diagramming the body of evidence in a case is now shown to be the central method for legal argument evaluation in the new dialectical system. Wigmore had contended that the logical structures of reasoning underlying the law of evidence could be traced back to the ancient logic of the Greek philosophers. In Chapter 4 it is shown how the notion of plausible reasoning, known since the time of the Greek skeptical philosophers but neglected for many centuries, is the key form of reasoning that underlies evidence law and legal argumentation. The ancient theory of plausible reasoning advocated cautious acceptance of an inference drawn plausibly from what seems to be true, subject to reservations.
According to this view of plausible reasoning, we can provisionally accept conclusions that seem to be true, even though we may be deceived occasionally. It is a view that is fallible, however: we need to be open-minded enough to give up the conclusion if new information comes in that indicates it is not true. For example, if a murder victim did not cry out for help before she was struck, the conclusion might be drawn by plausible reasoning that her assailant was not a stranger. This kind of reasoning is based on assumptions about what we can infer, given the way things can normally be expected to go in a kind of situation familiar to all of us as reasonable persons.
Plausible reasoning was widely familiar to the Greek and Roman philosophers and jurists but had pretty well disappeared from logic after the fall of the ancient world. Only recently has plausible inference come back into some prominence, through the reappearance of what is often called abductive reasoning in artiocial intelligence (AI) studies in computer science. Plausible reasoning is now widely used in AI, for example, in expert systems used for medical diagnosis. The expert system makes a guess by abduction, or inference to the best explanation, at a plausible diagnosis. But the hypothesis, or provisional guess, can be changed if new information comes in that indicates a different hypothesis is a better explanation of the facts known about the patient’s symptoms. Many important instances of legal reasoning are based on plausible inferences like those used in medical diagnosis.
Chapter 2 contains a list and description of the most common and important forms of plausible inference used in legal argumentation. In the past, most books on legal logic—with the notable exception of a few works like those of Perelman and Olbrechts-Tyteca (1969) and Alexy (1989)1—have concentrated almost exclusively on deductive or inductive logic in modeling legal argumentation. Deductive and inductive forms of inference were seen as central models of reasoning—or the only signiocant ones—by opinion leaders, evaluated from a semantic standpoint that abstracts an argument from its context of use in a particular case. The whole area of evidence law has been pretty well ignored, 1. New research initiatives in artiocial intelligence and law (Ashley 1990; Hage, Leenes, and Lodder 1994; Gordon 1995; Verheij 1996; Prakken 1997; Vreeswijk 1997; Lodder 1999) are also exceptions to this rule. Another exception is the work of Feteris (1999) on legal argumentation, therefore, by logicians—perhaps because, in the past, it seemed an impossible goal to model factors such as relevance of arguments. Even among those working in the more recently explored area of informal logic, the question ‘‘What is evidence?’’ has barely been asked.
I take a fresh approach to legal argumentation by treating evidence and relevance as central to the whole understanding of constructing a framework for the evaluation of legal arguments. The approach is dialectical in the ancient Greek sense, meaning that an argument is evaluated with respect to how it was supposedly used for a given purpose in a context of dialogue.2 Although forms of inference are seen as vitally important, how chains of inferences are used by a proponent and a respondent to persuade each other, or for various other communicative purposes, are presented as the basis for the evaluation of arguments. The central dialectical notion is that of commitment (rational acceptance in dialogue). Commitment is dialogical, and can be retracted, but has rational bite. If the respondent accepts the premises of the argument, and the form of the argument meets the appropriate structural requirements, then the respondent must accept the conclusion unless he can raise doubts about it by asking appropriate critical questions. A participant’s commitment to a statement is determined mostly by what he goes on record as saying in a dialogue but also partly by the goals and rules of the dialogue.
The focus of this book is on certain types of plausible argument that have, until recently, been generally considered fallacious in logic. Recent research is tending to show, more and more, that these types of argument are not always fallacious but that, in many instances, they are presumptively reasonable for shifting a burden of proof in a case. They tend to be arguments that, even when they are plausible, only shift a small weight of evidence from the premises to the conclusion of the argument. Even so, such arguments can be extremely important when lots of them are put together in a case.
For example, in a trial, one small argument may not prove much by itself. But a whole lot of these small arguments can yield a body of evidence that swings the burden of proof to one side or the other on a disputed issue. Using new ondings and methods of informal logic and argumentation theory, I show how to identify, analyze, and evaluate these kinds of plausible arguments that are so common, both in legal argumentation and in everyday experiences of conversational disputation. These types of arguments include familiar kinds of everyday arguments such as argument from position to know, argument from, 2. A dialogue is deoned as goal-directed type of conversational exchange in which two parties reason together, taking turns to ask questions, give replies, and put forward arguments to each other,ignorance, argument from precedent, argument from a rule to a particular case, appeal to expert opinion, appeal to pity, appeal to threat, argument against the person, causal argument, argument based on a verbal classiocation, argument from analogy, argument based on a deonition, and the slippery slope argument. This fresh approach reveals not only that such arguments are very often reasonable when used in a legal framework but are also most important and central among the kinds of arguments used in legal argumentation. Legal Argumentation and Evidence presents a new dialectical method of evaluating such arguments as they are used in legal contexts, offering a method of determining in each individual case of its use, whether the argument should be judged to be reasonable or fallacious. If the argument is weak but not so bad that it is fallacious, however, the new method tells you which critical questions should be asked in order to pinpoint specioc weaknesses.
This book should be of interest to anyone who is attempting to make sense of legal argumentation as a cooperative effort of several parties to reason with each other as speech partners. Not only lawyers but professionals and students in communication studies, linguistics (pragmatics), artiocial intelligence, logic, critical thinking, and philosophy will be interested readers. Among specialized groups, the analysis will appeal to those working in the law of evidence, and in the oeld of artiocial intelligence and law. But the general reader with no specialized training can easily read the book. Pre-law students, or anyone with an interest in legal argumentation, will ond it helpful as an introduction to the basic principle of legal reasoning and forms of argument. The presentation of material clearly explains all legal and logical jargon that is used, and is written in such a way that it can be read and understood by someone who does not have legal or logical training or expertise, but who wants to learn something about how argumentation works in the legal context. The orst chapter describes, for such a reader, the special features of argumentation in a legal system. The treatment is mainly set in the context of the Anglo-American common law system, but from time to time, comments are made about other systems. The book is meant to introduce people with a legal background to the latest developments in argumentation theory, and show them how this new oeld can be applied to many aspects of legal argumentation. But it is also useful to introduce anyone interested in argumentation and critical thinking to basic argumentation techniques used in many typical kinds of legal arguments often used as examples in informal logic textbooks.
© 2002 Penn State University