A CRITICAL REEXAMINATION OF DEFAULT LOGIC, AUTOEPISTEMIC LOGIC, AND ONLY KNOWING

Fifteen years of work on nonmonotonic logic has certainly increased ou r understanding of the area. However, given a problem in which nonmono tonic reasoning is called for, it is far from clear how one should go about modeling the problem using the various approaches. We explore th is issue in the context on two of the the best-known approaches, Reite r's default logic and Moore's autoepistemic logic, as well as two rela ted notions of ''only knowing'', due to Halpern and Moses and to Leves que. In particular, we return to the original technical definitions gi ven in these papers and examine the extent to which they capture the i ntuitions they were designed to capture.