Walton - Similiarity, Precedent And Argument From Analogy

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SIMILARITY, PRECEDENT AND ARGUMENT FROM ANALOGY
Douglas Walton Abstract In this paper, it is shown (1) that there are two schemes for argument from analogy that seem to be competitors but are not, (2) how one of them is based on a distinctive type of similarity premise, (3) how to analyze the notion of similarity using story schemes illustrated by some cases, (4) how arguments fromprecedent are based on arguments from analogy, and in many instances arguments from classification, and (5) that when similarity is defined by means of story schemes, we can get a clearer idea of how it integrates with the use of argument from classification and argument from precedent in case-based reasoning by using a dialogue structure. Key words: stories; case-based reasoning; argument fromclassification; argumentation. CRRAR University of Windsor

This paper is about the logical structure of argument from analogy and its relationship to legal arguments from classification and precedent. Its main purpose is to provide guidance for researchers in AI and law on which argumentation scheme for argument from analogy to use, among the leading candidates that are currently available. Argumentsfrom precedent cases to a case at issue are based on underlying arguments from analogy of a kind extremely common both in everyday conversational argumentation and in legal reasoning. There is a very large literature on argument from analogy in argumentation (Guarini et al., 2009), and the topic is fundamentally important for law because of the centrality of arguments from precedent and analogy inAnglo-American law. It is not hard to appreciate this connection, given that according the rule of stare decisis, the precedent decision of a higher or equal court is binding on a similar current case (Ashley, 1988, 206). In this paper, cases are used to argue that arguments from precedent are based on arguments from analogy in legal reasoning, and that arguments from analogy are based on asimilarity between the two cases held to be analogous. As shown in the paper, this claim is controversial, because there are different views about how the argumentation scheme for argument from analogy should be formulated (Macagno and Walton, 2009). According to the version of the scheme for argument from analogy argued to be the basic one in this paper, one of the premises has a requirement holding thatthere is a similarity between the two cases in point. In this paper I show how to analyze this notion of similarity using the story-based approach of Bex (2009) and the formal dialogue model for investigating stories of Bex and Prakken (2010). It is shown how an abstract structure called a story scheme can be employed in a way that makes it useful to identify, analyze and evaluate arguments fromanalogy, and show their function in case-based reasoning where precedents are involved. In Popov v Hayashi (Popov v. Hayashi 2002 WL 31833731 (Cal. Superior, Dec. 18, 2002)),

Electronic copy available at: http://ssrn.com/abstract=1752964

2 a case that has become a benchmark in AI and law (Gordon and Walton, 2006a; Wyner, BenchCapon and Atkinson, 2007), the issue concerned which fan hadownership rights to a home run baseball hit into the stands by Barry Bonds while the precedent cases concerned the hunting and fishing of wild animals. A problem posed is that the baseball case and the animals cases don’t seem all that similar to each other at first sight, even though it can be argued that they are similar (or not) in certain respects. The problem is to specify exactly how they aresimilar, or are supposed to be, in an argument from a precedent case to a case being decided, when the relationship between the two cases is thought to be one of similarity. Ashley (2009, 1), referring to one of the animals cases, posed the problem in the question: “How is Barry Bonds’ 73rd home run like a fox in a fox hunt?” The problem is to clearly define similarity in such a way that it can...