Speaker:     Patrick Girard
Affiliation: The University of Auckland
Title:       Logical dynamics of belief change in the community
Date:        Monday, 21 May 2012
Time:        4:00 pm
Location:    Room 6115, Owen Glenn Building

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 influence’. In particular, we focus on the question of what makes the beliefs of a community stable under various dynamical situations. Besides, we  consider refinements and alternatives to the `threshold’ model. The most significant alternative is to move to consideration of plausibility judgements rather than mere beliefs. We show first that some such change is mandated by difficult problems with belief-based dynamics related to the need to decide on an order in which different 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.