Changing Conditional Beliefs Unconditionally

Abstract

Although the AGM account of belief change tells us how to change unconditional beliefs, it fails to guide us in changing our conditional beliefs. That explains why, in the AGM account of belief change proper, a decent account of iterated belief change is not forthcoming. Darwiche and Pearl provide an account of changing conditional beliefs. We argue that the Darwiche-Pearl postulates are, on the one hand, limited in scope and, on the other, excessively strong and suggest how they should be supplemented. We show, contrary to the generally held view, that the revision operation changes to a new (though in some cases the same) revision operation after each instance of belief change. Finally, we prove what may be viewed as representation results connecting the acount offered in this paper with entrenchment kinematics.