  This brief historical introduction to nonmonotonic logic leaves untouched a number of general topics that might well be of interest to a nonspecialist. These include graph-based and proof-theoretic approaches to nonmonotonic logic, results that interrelate the various formalisms, complexity results, tractable special cases of nonmonotonic reasoning, relations between nonmonotonic and abductive reasoning, relations to probability logics, the logical intuitions and apparent patterns of validity underlying nonmonotonic logics, and the techniques used to formalize domains using nonmonotonic logics. For these and other topics, the reader is referred to the literature. As a start, the chapters in  Gabbay et al. 1994  are highly recommended.