Belief Revision: A Critique

  • Authors:

  • Nir Friedman;Joseph Y. Halpern

  • Affiliations:

  • Computer Science Division, University of California, 387 Soda Hall, Berkeley, CA 94720, U.S.A. E-mail: nir@cs.berkeley.edu/ http://www.cs.huji.ac.il/&sim/nir;Computer Science Department, Cornell University, Ithaca, NY 14853, U.S.A. E-mail: halpern@cs.cornell.edu/ http://www.cs.cornell.edu/home/halpern

  • Venue:
  • Journal of Logic, Language and Information
  • Year:
  • 1999

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Abstract

We examine carefully the rationale underlying the approaches to belief change taken in the literature, and highlight what we view as methodological problems. We argue that to study belief change carefully, we must be quite explicit about the ’’ontology‘‘ or scenariounderlying the belief change process. This is something that has beenmissing in previous work, with its focus on postulates.Our analysis shows that we must pay particular attention to twoissues that have often been taken for granted: the first is how we model the agent‘s epistemic state. (Do we use a set of beliefs, or aricher structure, such as an ordering on worlds? And if we use a set ofbeliefs, in what language are these beliefs are expressed?)We show that even postulates that have been called ’’beyondcontroversy‘‘ are unreasonable when the agent‘s beliefs include beliefs about her own epistemic state as well as the external world.The second is the status ofobservations. (Are observations known to be true, or just believed? Inthe latter case, how firm is the belief?) Issues regardingthe status of observations arise particularly when we consideriterated belief revision, and we must confront the possibilityof revising by &phis; and then by ¬ &phis;.