Worlds of knowing and nonmonotonic reasoning

The project of formalizing nonmonotonic reasoning on the basis of historical and contemporary philosophical reflections on reasoning and knowing is examined. Some paradigmatic accounts of the prospects of formalizing reasoning, from the ancient beginnings of western epistemology up to contemporary debate about the reasonableness of scientific development, are reviewed. Implications of these historical and philosophical reflections for the project of formalizing nonmonotonic reasoning are then sketched. The contention defended is that, because of the inevitable conventionality involved in distinguishing between revisable and nonrevisable rules, this formalizing is best viewed as an art dependent upon background knowledge of a world. In conclusion, certain symptoms of this worldly knowledge, constituting the limits both of the art of knowledge engineering and of philosophical analysis, are advanced