An Internal Version of Epistemic Logic

摘要

Representing an epistemic situation involving several agents obviously de-pends on the modeling point of view one takes. We start by identifying the types of mod-eling points of view which are logically possible. We call the one traditionally followedby epistemic logic the perfect external approach, because there the modeler is assumedto be an omniscient and external observer of the epistemic situation. In the rest of thepaper we focus on what we call the internal approach, where the modeler is one of theagents involved in the situation. For this approach we propose and axiomatize a logicalformalism based on epistemic logic. This leads us to formalize some intuitions about theinternal approach and about its connections with the external ones. Finally, we show thatour internal logic is decidable and PSPACE-complete.