  Neither Doyle or McDermott pursued the modal approach much beyond the initial stages of  McDermott 1982, and  McDermott &amp; Doyle 1980.  With a helpful suggestion from Robert Stalnaker (see  Stalnaker 1993),  however, Robert C. Moore produced a modal theory that improves in many ways on the earlier ideas. Moore gives the modal operator of his system an epistemic interpretation, based on the conception of a default rule as one that licenses a conclusion for a reasoning agent unless something that the agent knows blocks the conclusion. In Moore’s autoepistemic logic, an extension E of a theory T is a superset of T that is stable, i.e., that is deductively closed, and that satisfies the following two rules: