Epistemic Entrenchment and the Possible Models Approach

The Possible Models Approach (PMA) introduced by Winslett, proposes, among other things, a domain-independent criterion for measuring the similarity between the diierent states of a dynamic system. Based on this criterion of similarity, the PMA makes inferences about the eeects of events in the system. The concept of similarity between states (possible worlds) appears also in the area of Belief Revision in the form of a system of spheres. Systems of spheres are in turn connected to epistemic entrenchments by means of the AGM revision functions that the two structures induce. In view of these connections, in this article we identify and study the properties of the family of epistemic entrench-ments corresponding to systems of spheres that comply with PMA's criterion of similarity. Using the results established herein, we then outline a version of the PMA based on epistemic entrenchments.