A Formal Theory of Plan Recognition

The problem of recognizing an agent's plans arises in many contexts in work in artificial intelligence. The plan recognition techniques suggested in the literature are rarely formally justified. We view plan recognition as a special kind of non-monotonic reasoning, and demonstrate how formal techniques developed for such reasoning-- namely, circumscription and minimal entailment-- can be used in plan recognition. The first half of this paper reviews a broad range of work in artificial intelligence and philosophy which relates to plan recognition. A formal treatment of a simple case of plan recognition follows, and the paper concludes with proposals for future extensions of thi