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Coalition and Epistemic Logic: An Intensional Approach to Groups

GF22-23022L [Registered results] [WWW] 2022 - 2025

The project will lift an important and up to now largely overlooked idealization in logical models of group knowledge and action - the extensional view of groups where a group is reduced to the set of its members. Consequently, groups change identity when their membership changes, any uncertainty regarding who is in a given group is ruled out and the structure of groups is not reflected. However, firms, informal teams or even loose crowds typically remain even if they gain or lose members, and the identity of all members is rarely common knowledge in any group of moderate size. In order to lift this idealization the project will study an intensional view of groups, which loosens the relationship between group membership and group identity and takes into account its algebraic or relational structure, and apply this view to questions in multiagent epistemic logic (distributed and common knowledge, perfect recall) and coalition logic (groups’ agentive powers). It will allow for more natural applications of logical models to questions of collective memory, action and responsibility.