Reasoning About The E ects of Communication On Beliefs

Perrault[2] has presented a formal framework describing communicative action and the change of mental state of agents participating in the performance of speech acts. This approach, using an axiomatization in default logic, su ers from several drawbacks dealing with the persistence of beliefs and ignorance over time. We provide an example which illustrates these drawbacks and then present a second approach which avoids these problems. This second approach, an axiomatization of belief transfer in a nonmonotonic modal logic of belief and time, is a reformulation of Perrault's main ideas within a logic which uses an ignorance-based semantics to ensure that ignorance is maximized. We present an axiomatization of this logic and describe the associated techniques for nonmonotonic reasoning. We then show how this approach deals with inter-agent communications in a more intuitively appealing way.