Logical dynamics of belief change in the community

Abstract

In this paper we explore the relationship between norms of belief revision that may be adopted by members of a community and the resulting dynamic properties of the distribution of beliefs across that community. We show that at a qualitative level many aspects of social belief change can be obtained from a very simplistic model, which we call `threshold in uence'. In particular, we focus on the question of what makes the beliefs of a community stable under various dynamical situations. Besides, we consider re nements and alternatives to the `threshold' model. The most signi cant alternative is to move to consideration of plausibility judgements rather than mere beliefs. We show rst that some such change is mandated by di cult problems with belief-based dynamics related to the need to decide on an order in which di erent beliefs are considered. Secondly, we show that the resulting plausibility-based account results in a dynamical system that is non-deterministic at the level of beliefs. Nonetheless, the plausibility-based account lacks certain intuitively desirable features, such as the preservation of the transitivity.