Eduardo L. Fermé Five Faces of Recovery

One of the basic principles of the AGM theory [Alchourrón et al., 1985] is that belief changes should take place with minimal loss of previous beliefs. In the opinion of the AGM trio, the postulate of recovery guarantees minimal loss of contents in the contraction process.1 However, several authors have criticised the recovery postulate [Fermé, 1998; Makinson, 1987; Levi, 1991; Levi, 1997; Lindström and Rabinowicz, 1991; Hansson, 1991; Niederée, 1991; Nayak, 1994; Makinson, 1997]. The present work describes recovery from five angles or models in which it is possible to define the AGM contraction: Postulates, partial meet functions, epistemic entrenchment, safe/kernel contraction and sphere-systems. It also shows how the intuitions or non-intuitions that surround recovery appear or disappear in each of them and consequently, the status of recovery turns out to differ substantially among the five approaches. In Section 2 we introduce AGM contraction in its five presentations, and in Sections 3 to 7 we analyse recovery in the five AGM presentations.