Varieties of group knowledge

Abstract

The addition of a social dimension to knowledge has most impact when considering the knowledge of more than one agent. We survey known epistemic distinctions concerning the knowledge of groups, such as that between common, distributed and general knowledge, and their relationship to types of communication, such as public and private announcement, and disclosure. This opens the question of how the knowledge or uncertainty of agents about a channel of communication contributes to different kinds of group knowledge. We look at a number of sources of uncertainty: about the message, the receivers, the source, and the knowledge of the source, paying attention to indexical and de re / de dicto distinctions. In doing so we construct a complex epistemic anatomy of a channel, but one that can be elegantly described in the formal language of social epistemic logic. Finally, we introduce a number of concepts related to group knowledge: the potential knowledge of an agent within a social structure, the notion of common distributed knowledge, and the hierarchy of iterations of "common" and "distributed", illustrated by examples of social interaction that induce them. This is base on joint work with Liu Fenrong (Tsinghua).