Credulous vs. Sceptical Semantics for Ordered Logic Programs

We present a semantic approach to the characterization of credulous and sceptical reasoning mechanisms, within the framework of ordered logic. One of the advantages of our approach is that it integrates thightly with "conservative" ordered logic semantics which is known to generalize "classical" (stable and wellfounded) logic programming semantics. This allows us to compare the conservative and credulous approaches, thus providing insight in the fundamental properties of both reasoning paradigms. It turns out that maximal credulous models are extensions of conservative stable models while the (unique) minimal credulous model, called the sceptical model, is a restriction of the well-founded model.