Report Number: CS-TR-88-1237
Institution: Stanford University, Department of Computer Science
Title: Belief as Defeasible Knowledge
Author: Shoham, Yoav
Author: Moses, Yoram
Date: December 1988
Abstract: We investigate the relation between the notions of knowledge and belief. Contrary to the well-known slogan about knowledge being "justified, true belief," we propose that belief be viewed as defeasible knowledge. Specifically, we offer a definition of belief as knowledge-relative-to-assumptions, and tie the definition to the notion of nonmonotonicity. Our definition has several advantages. First, it is short. Second, we do not need to add anything to the logic of knowledge: the right properties of belief fall out of the definition and the properties of knowledge. Third, the connection between knowledge and belief is derived from one fundamental principle, which is more enlightening than a collection of arbitrary-seeming axioms relating the two notions.