Proceedings of the Annual Meeting of the Cognitive Science Society

In this paper we focus on the Distinguisher 's Wedge, an intellectual tool for responding to an argument that two cases are alike by asserting reasons why they are different and why the differences matter. W e characterize the wedge as involving a search for distinctions, factual differences between the cases that tie into justifications for treating them differently. W e show how the wedge can be modelled computationally in a Case-Based ReEisoning ("CBR") system using precerfenh'a/justifications and describe how the model is realized in our H Y P O program which performs legal reasoning in the domain of trade secret law. Legal argument, with its emphzisis on citing and distinguishing precedents and lack of a strong domain model, is an excellent domain for studying the wedge. W e show how H Y P O uses "dimensions", "case-analysis-record" and "claim lattice"mechanisms to cite and distinguish real cases and suggest how the model may be extended to cover more sophisticated kinds of distinguishing.