Epistemic Entrenchment in Autoepistemic Logic

Abstract

A drawback of existing epistemic logics is their inability to deal with entrenchment of beliefs. All beliefs have equal status; none can be held more firmly than others. We present a bimodal logic that generalizes Levesque’s reconstruction of autoepistemic logic. In our system standard epistemic concepts can be represented, including the notion of only knowing, but elements of a belief set may be more or less entrenched. This has important implications for the distinction between epistemic defaults and subjunctive (and normative) defaults, both of which are representable in our system.