Probabilistically Reliable Default Reasoning

This paper superimposes an assumption generation mechanism (AGM) and a lower bound propagation mechanism (LBM) on default reasoning. AGM generates minimal probabilistic assumptions which are needed to derive default conclusions safely, and LBM supplies (approximately) tight lower probability bounds of the conclusions. Together both mechanisms make default reasoning probabilistically reliable. The underlying logical framework is an extension of Adams’ probability logic P by irrelevance and contraposition assumptions, called the system P DP. There is an exact correspondence between Poole-extensions and P DP-extensions. The procedure for P DPentailment is comparable in complexity with Poole’s procedure.