Modelling Legal Argument: Reasoning with Cases and Hypotheticals
MASSACHUSETTS UNIV AMHERST DEPT OF COMPUTER AND INFORMATION SCIENCE
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This dissertation is about adversarial, case-based reasoning and the HYPO program that performs adversarial reasoning with cases and hypotheticals in the legal domain. The dissertation identifies and describes basic case-based operations, an adversarial, case-based reasoning process, a schematic structure for case-based arguments, the kinds of counter-examples that arise and the knowledge sources necessary to support adversarial, case-based reasoning. The HYPO program embodies the methodology. It comprises 1 a structure Case Knowledge Base CKB of actual legal cases 2 an indexing scheme dimensions for retrieval of relevant cases from the CKB 3 methods for analyzing problem situations and retrieving relevant cases 4 methods for interpreting and assessing the relevancy of past cases by positioning the problem with respect to relevant existing cases in the CKB as seen from the viewpoint of the problem at hand and finding the most-on-point cases 5 methods for comparingcontrasting cases e.g., citing, distinguishing, finding counter-examples 6 methods for posing hypotheticals that test the sensitivity of the problem situation to changes, particularly with regard to potentially adverse effects of new damaging facts coming to light and existing favorable ones being discredited 7 methods for generating 3-ply argument outlines to play out realistic legal arguments citing cases in a manner familiar to attorneys and 8 methods for explaining alternative decisions of the problem situation by posing hypothetical, comparing arguments and summarizing the procedures. HYPOs performance compares favorably to that of judge and attorneys in actual legal cases.