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Argumentation Schemes


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Argumentation Schemes
Cambridge University Press
9780521897907 - Argumentation Schemes - By Douglas Walton, Chris Reed and Fabrizio Macagno

Introduction: Argumentation Schemes

The theory of argumentation is a rich interdisciplinary area of research spanning philosophy, communication studies, linguistics, computer science, and psychology. In the past few years, formal models of argumentation have been steadily gaining importance in artificial intelligence, where they have found a wide range of applications in specifying semantics for logic programs, generating natural language text, supporting legal reasoning, and facilitating multi-agent dialogue and negotiation on the Internet.1 The most useful and widely used tool so far developed in argumentation theory is the set of argumentation schemes. Argumentation schemes are forms of argument (structures of inference) that represent structures of common types of arguments used in everyday discourse, as well as in special contexts like those of legal argumentation and scientific argumentation.2 They include the deductive and inductive forms of argument that we are already so familiar with in logic. However, they also represent forms of argument that are neither deductive nor inductive, but that fall into a third category, sometimes called defeasible, presumptive, or abductive. Such an argument may not be very strong by itself, but may be strong enough to provide evidence to warrant rational acceptance of its conclusion, given that its premises are acceptable (Toulmin, 1958). Such an argument can rightly carry weight, or be a plausible basis

for acceptance, on a balance of considerations in an investigation or discussion that is moving forward, as new evidence is being collected. The investigation can then move ahead, even under conditions of uncertainty and lack of knowledge, using the conclusion tentatively accepted.

To use a phrase from Anderson, Schum, and Twining (2005, p. 262), such presumptive arguments are necessary but dangerous. We need to use them as heuristics that provide rational grounds for accepting a conclusion tentatively even if it has not been conclusively proved, but we have to remain open-minded when we use such arguments, because they are fallible and inherently subject to default. A defeasible argument is one in which the conclusion can be accepted tentatively in relation to the evidence known so far in a case, but may need to be retracted as new evidence comes in. A typical case of a defeasible argument is one based on a generalization that is subject to qualifications. Should it come to be known that the present case is an exception to the generalization, the argument defaults, and its conclusion must be retracted. Defeasible arguments are especially prominent in legal and ethical reasoning, but they are everywhere, even in science, especially at the discovery stage of an investigation.

The recognition of the importance and legitimacy of defeasible argumentation has led to a recent paradigm shift in logic, artificial intelligence, and cognitive science. Common forms of defeasible arguments were long categorized as fallacious in logic textbooks. It is been only recently that, as these informal fallacies have been studied more intensively, more and more instances have been recognized where the forms of argument underlying them are reasonable, but inherently defeasible. For example, arguments based on expert opinion have long been categorized in logic textbooks under the heading of fallacious appeals to authority. However, it is clear that for practical purposes in everyday reasoning, and in many of our social and intellectual institutions, we could not get by without such arguments. Expert testimony, including ballistics evidence, DNA evidence, and many other forms of testimony by scientific experts, has become a dominant kind of evidence in the courts. It has become so dominant as evidence that it is on the verge of overwhelming our judicial system. Clearly, it is not helpful to condemn such evidence as inherently fallacious. Rather, the problem is to judge in specific cases when an argument from expert opinion can properly be judged to be strong, weak, or fallacious. Hence the importance of argumentation schemes has become readily apparent in recent years, as this

paradigm shift about rational argumentation has affected many fields, including law, cognitive science, artificial intelligence, logic, philosophy of science, and indeed any field where standards of rational argument are centrally important.

There has emerged in recent years a considerable body of work on informal fallacies, collecting together a large corpus of examples, along with tools to identify, analyze, and evaluate the arguments in those examples. Clearly, this body of work provides a huge database, and repository of other materials, including many argumentation schemes, that are fundamental to any attempt to approach the project of providing a systematic overview of the current state of the art of research on argumentation schemes. The special advantage of the present book is that it builds on this previous research on fallacies, moving through the paradigm shift to the new idea of coping with the revolutionary notion that such “fallacies” are no longer fallacies.

Although this is the first book to bring together such a large number of schemes and to analyze and study them in such depth, even to the point of starting the project of classifying and formalizing schemes, prior works on schemes do exist. In a book on presumptive argumentation schemes by one of the authors (Walton, 1996), a list of twenty-six defeasible argumentation schemes was presented and analyzed. Among them are such common forms of argument as argument from sign, argument from example, argument from commitment, argument from position to know, argument from expert opinion, ad hominem argument, argument from analogy, argument from precedent, argument from gradualism, and several types of slippery slope argument. Each argument of this type is presented as providing only a defeasible support for its conclusion, subject to critical questioning in a context of dialogue. Matching each argumentation scheme is an appropriate set of critical questions. The method of studying defeasible argumentation schemes through the use of a set of matching critical questions can be credited to Hastings (1963). Arthur Hastings, in his innovative Ph.D. thesis at Northwestern University in 1963, set out a useful list of many of these schemes, with illustrative examples, and with a set of critical questions corresponding to each scheme. The method of evaluation of an argument fitting a scheme is that once the argument is put forward by a proponent, it may be defeated if the respondent asks an appropriate critical question that is not answered by the proponent. Hastings’ approach seemed to have been ignored for many years, but as the field of argumentation studies

developed, other researchers began to adopt his approach. For example, Kienpointner (1992) and Grennan (1997) produced comprehensive lists of schemes, stressing deductive and inductive forms.

This book takes a much more comprehensive and in-depth approach than any previous treatment of schemes. In Chapter 9, a compendium of schemes has been produced that presents sixty-five schemes. They are presented in a form that can easily be used by all of those who are interested in schemes or are working on them. Nearly all of the schemes in the compendium have been collected from the already existing literature, although there are a few new ones. Here, for the first time, they are brought together in one place. Chapter 1 introduces the beginning reader to schemes, and describes the basic tools of argumentation research needed to formulate the schemes more precisely and to understand how they work. All concepts in Chapter 1 are explained from the ground up, so that the beginning reader can understand the chapters that follow. The reader can next, in Chapter 2, gain further insight into how schemes work and how they are to be analyzed by examining the treatment of one of the most fundamental schemes, that for argument from analogy. Argument from analogy is especially important in law, notably in our Anglo-American justice system, where court decisions are arrived at by comparing a given case with a previously decided one. Thus Chapter 2 also reveals the importance of this particular argumentation scheme and the wide-ranging nature of the application of defeasible argumentation schemes.

Chapter 2 begins with a typical example of a legal decision by the courts that is based on argument from analogy. When a trained dog sniffs luggage in a public place and signals to the police that it contains drugs, should this event be classified as a search? The question is decided by comparing the case, by analogy, to previous cases that have already been decided by the courts. Previously, the logical literature on argument from analogy has tended to classify this form of argument as either deductive or inductive. We propose a new way of classifying it by treating it as a defeasible argumentation scheme that can hold tentatively on the balance of considerations, thus influencing future decisions without finally closing the issue one way or the other. By using tools developed in argumentation theory and artificial intelligence, we show how argument from analogy, as used in legal reasoning in typical cases, is closely associated with other argumentation schemes. Especially prominent, as shown by our analysis of these cases, are the argumentation schemes for verbal classification and argument from precedent. We are thus able to show,

in a much deeper way than has been possible in the past, how argument from analogy, allied with these other argumentation schemes, provides new logical foundations for case-based reasoning in law.

Chapters 3, 4, and 5 describe many of the most common and important defeasible argumentation schemes, providing many examples to show how they work in everyday argumentation. Chapters 6 and 7 study two concepts that are not only fundamental to understanding how schemes work, but that also show how important schemes are as building blocks of the most common kinds of arguments. Chapter 6 shows how schemes can be used to help identify premises or conclusions that are implicitly assumed, but that have not been explicitly stated as part of an argument. Chapter 7 is about the notion of argument rebuttal. In other words, it is all about how one argument confronts and attacks, and possibly even defeats, another argument by adducing reasons that show that the other argument is not tenable. Some argumentation schemes have the specific purpose of functioning as rebuttals to other arguments. Although the notion of argument rebuttal is fundamental to the study of all rational argumentation, there are many controversies and disagreements about how it should precisely be defined, and the notion has never been clarified fully throughout the long history of the subject.

As we show in Chapter 8, the study of schemes has a long history going back to Aristotle's topics – common types of argument, often called commonplaces, that Aristotle saw as fundamental building blocks in a branch of logic he called dialectic. Aristotle also developed formal logic through his theory of the syllogism, and that approach to logic came to dominate the whole field, and indeed the intellectual scene generally, through the Middle Ages. As deductive logic became formalized in the twentieth century, the study of dialectic continued to be ignored. Although informal fallacies, as noted earlier, continued to be treated in the logic textbooks, the study of topics remained in a somewhat confused state, never gaining wide acceptance as a tool for the analysis of rational argumentation. Many had hoped that topics could be used as a tool for the discovery of new arguments, a technique for argument invention. This would be an extremely useful tool in many fields, but only with the advent of this book has it become a practical possibility.

The problem so far in modern argumentation studies is that the schemes have been developed in a rough-and-ready way. They have been meant to be practical tools to help students learn skills of argumentation and critical thinking by recognizing common forms of argument and by being able to criticize them by asking standard critical questions that

probe the weak points of an argument. Such a practical tool has proved to be extremely useful, but if schemes are to be exploited by more exact fields like logic and artificial intelligence, they need to be defined and analyzed in a more precise and systematic manner. Indeed, as we show in Chapter 10, a systematic method of classifying schemes is a top priority, and the current work in artificial intelligence is developing methods for the formalization of schemes. These efforts, culminating in this book, represent the frontiers of the new research on schemes, aiming at the goal of developing tools for argument search in natural texts and for argument invention.

This volume surveys all aspects of argumentation schemes from the ground up, taking the reader from the elementary exposition of the first chapter to the latest state of the art in the research efforts to formalize and classify the schemes as outlined in the last three chapters. In Chapter 8, the history of schemes is surveyed, so that the reader can grasp how, even though their study was very much in the background for two millennia, there was active work on them during both the ancient and medieval periods. In Chapters 2 through 5 we pick out what we take to be the most important and common schemes, and analyze and discuss these schemes up to the present point of research on them. In Chapters 6 and 7 we discuss two underlying concepts, those of enthymeme and rebuttal, that are fundamentally important in helping us to understand the common structure that the schemes share and the promise that they hold as argumentation tools. Thus the whole book gives a panoramic survey of the state of the art of current research on schemes, from the ancient roots of the subject to recent research developments. It is a necessary tool for anyone interested in argumentation schemes, in the many fields that use them, and in the many other fields that will.

1 Recent conferences and workshops dedicated to the theory of argumentation in artitifical intelligence include the International Conference on Computational Models of Argument (COMMA 2006), the Computational Models of Natural Argument (CMNA) workshop series, and the Argumentation in Multi-Agent Systems (ArgMAS 04, 05, and 06) workshop series. In 2007, there has been a call for papers for a special issue of the IEEE journal Intelligent Systems on the topic of argumentation technology.

2 Prakken (2005) has shown that because logic is too abstract to apply very effectively to legal argumentation, research in AI and law needs to be supplemented by an argumentation schemes approach.

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