mklein@AISUNG.CS.UIUC.EDU (Mark Klein) (11/04/86)
My understanding of nonmonotonic reasoning (NMR) is different from what you described in a recent ailist posting. As I understand it, NMR differs from monotonic reasoning in that the size of the set of true theorems can DECREASE when you add new axioms - thus the set size does not increase monotonically as axioms are added. It is often implemented using truth maintenance systems (TMS) that allow something to be justified by something else NOT being believed. Monotonic reasoning, by contrast, could be implemented by a TMS that only allows something to be justified by something else being believed. Default reasoning is an instance of nonmonotonic reasoning. Nonmonotonic reasoning is thus not synonymous with truth maintenance. Mark Klein