p-92-02 Using Goals and Experience to Guide Abduction Indiana University Computer Science Department Technical Report number 359, July 1992. David B. Leake Abstract: Standard methods for abductive understanding are neutral to prior experience and current goals. Candidate explanations are built from scratch by backwards chaining, without considering how similar situations were previously explained, and selection of the candidate to accept is based on its likelihood, without considering the information needs beyond routine understanding. Problems arise when applying these methods to everyday understanding: The vast range of possible explanations makes it difficult to control the cost of explanation construction and to assure that the explanations generated will actually be useful. We argue that these problems can be overcome by using goals and experience to guide both explanation generation and evaluation. Our work is within the framework of case-based explanation, which builds explanations by retrieving and adapting prior explanations stored in memory. We substantiate our model by describing mechanisms that enable it to effectively generate good explanations. First, we demonstrate that there exists a theory of anomaly and explanation that can guide retrieval of relevant explanations. Second, we present a plausibility evaluation process that efficiently detects conflicts and confirmations of an explanation's assumptions by prior patterns, making it possible to focus explanation adaptation when retrieved explanations are implausible. Third, we present methods for judging whether explanations provide the information needed to satisfy explainer goals beyond routine understanding. By reflecting experience and goals in the search for explanations, case-based explanation provides a practical mechanism for guiding search towards explanations that are both plausible and useful. A postscript file for the full paper is available electronically. To get a copy by anonymous ftp, see ftp://ftp.cs.indiana.edu/pub/leake/README. on the web, open URL ftp://ftp.cs.indiana.edu/pub/leake/INDEX.html.