Defeasible reasoning

a philosophical analysis in prolog

Donald Nute

pp. 251-288

in: James H. Fetzer (ed), Aspects of artificial intelligence, Berlin, Springer, 1988

Abstract

We reason defeasibly when we reach conclusions that we might be forced to retract when faced with additional information. I contrast this with both invalid deductive reasoning and inductive reasoning. This reasoning is defeasible, but its defeasibility is not because of incorrectness. Nor is it ampliative as is inductive reasoning. It is the kind of "other things being equal" reasoning that proceeds from the assumption that we are dealing with the usual or normal case. Conclusions based on this kind of reasoning may be defeated if we find that the situation is not usual or normal.