Hypotheticals as Heuristic Device

Hypotheticals as Heuristic Device Edwina L. Rissland and Kevin D. Ashley Department of Computer and Information Science University of Massachusetts Amherst, MA 01003 Abstract In this paper we examine the use of hypotheticals as a heuristic device to assist a case-based reasoner test the strengths, weaknesses, and ramifications of an analysis or argument by exploring and augmenting the space of known cases and indirectly, the attendant spaces of doctrine and argument. Our program, HYPO, works in the task domain of the law, particularly, the area of trade secret protection for software. We describe how HYPO generates a constellation of legally-meaningful hypothetical fact situations ("hypos") which are "near" a given fact situation. This is done in two steps: analysis of the given situation and then generation of the hypos. We discuss the heuristics HYPO currently uses, which include: (1) make a case weaker or stronger; (2) generate an extreme case; (3) generate a near miss; (4) manipulate a near win; and (5) generate a case on a related "dimension". I. Introduction HYPO is a program to model reasoning with cases and hypotheticals ("hypos"). The program comprises a means of representing and indexing cases in a Case Knowledge Base ("CKB"), a computational definition of relevance in terms of "dimensions" which capture the utility of a case for making a particular kind of argument, a dimension-based method for comparing cases, and methods for generating hypotheticals to help an arguer formulate an argument, gather relevant facts, and explain his argument. HYPO's domain is legal argument where, as illustrated below with examples of oral arguments before the Supreme Court,-cases and hypotheticals are primary tools. In this paper, we concentrate on HYPO's creation of hypothetical new cases to accomplish such tasks as: (1) test the sensitivity of one's argument to absence or presence of certain facts; (2) locate and explore subspaces of relevant cases in the CKB; (3) augment and "flesh out" sparse areas of the CKB; (4) sample the space of implications of a given argument; (5) formulate refinements and refutations of an argument. Thus, we are using hypotheticais as a heuristic device to explore several "spaces" -- the CKB itself, and the spaces of legal doctrine and argument -- and to acquire new case knowledge. HYPO generates these hypotheticals heuristically using certain well-known general heuristics (e.g., examine extreme cases) as well as HYPO-specific ones (e.g., examine weaker/stronger cases along a HYPO dimension). While HYPO is a program whose primary task domain is legal argument, the lessons learned from HYPO should prove useful for other case-oriented tasks like strategic planning and learning by experimentation. The posing and manipulating of hypotheticals is important in strategic planning where one must examine a proposed plan in light of telling what ifs -- all too often the advocate of a plan only tells of its good points and and a devil's advocate is needed to unmask its weaknesses. In learning, some of the questions concerning how to intelligently select examples as training instances have a large overlap with our …

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