Inside the Black Box
This is the first of two chapters devoted to problems in the currently dominant model of belief change (the AGM model) that justify the development of alternative frameworks for belief change. In this chapter the focus is on the selection mechanisms that are used to determine which previous beliefs are retained and which are given up in operations of change. In the AGM model, such epistemic choices are assumed to be performed in two steps (the select-and-intersect method). First, a selection is made among a set of logically infinite objects of choice (remainders or possible worlds) that are not themselves representations of plausible belief states. This is followed by a second step in which the outcome is obtained by intersecting the objects that were chosen in the first step. The plausibility of this sequence of operations is critically examined, and the formal limits to its applicability are also pointed out. One of its problems is that epistemic choiceworthiness is not in general preserved under intersection. It is argued that epistemic choices should instead be represented as choices directly among the potential outcomes of the operation of change, i.e., choices among potential belief states.