armin@csri.toronto.edu (Armin Haken) (03/23/88)
AI Seminar: 2PM, Thursday March 31, Galbraith room 304 A Semantic Basis for Explicit Belief James P. Delgrande School of Computing Science, Simon Fraser University, Burnaby, B.C., Canada V5A 1S6 A general framework for the investigation of logical systems of belief that are both tractable and semantically well-motivated is presented. The approach extends standard possible worlds semantics in two ways. First, partial possible worlds, or situations, are employed. Second, the set of situations used to determine the truth of an explicit belief, B alpha, at a situation depends in part on the proposition expressed by alpha. It is argued that the approach is provides a uniform semantics from which systems may be constructed, contrasted, and compared. Proofs of soundness and completeness are given directly in terms of this semantics and not, as is the case with previous work, by appealing to similar results in relevance logic. Thus the formal results also provide a connection between the semantic theory of possible worlds and that of relevance logic. Given this framework, we propose a specific system, BRPK, as a "preferred" model of explicit belief. This system arguably retains a strong intuitive basis, while avoiding the (perceived) pitfalls of earlier systems. Moreover it is tractable and permits iterated modalities.