This essay argues that in linguistic communication, nothing corresponds to a linguistic competence as summarized by the three principles of first meaning in language: that first meaning is systematic, first meanings are shared, and first meanings are governed by learned conventions or regularities. There is no such a thing as a language, not if a language is anything like what many philosophers and linguists have supposed. We must give up the idea of a clearly defined shared structure which language users (...) acquire and then apply to cases, as well as the attempt to illuminate how we communicate by appeal to conventions. (shrink)

In this paper we introduce Dynamic Epistemic Logic, which is alogic for reasoning about information change in a multi-agent system. Theinformation structures we use are based on non-well-founded sets, and canbe conceived as bisimulation classes of Kripke models. On these structures,we define a notion of information change that is inspired by UpdateSemantics (Veltman, 1996). We give a sound and complete axiomatization ofthe resulting logic, and we discuss applications to the puzzle of the dirtychildren, and to knowledge programs.