Nonmonotonic inference based on expectations

摘要

We show how nonmonotonic inferences may elegantly be interpreted in terms of underlying expectations. The fundamental idea is that when we reason, we make use of not only the information that we firmly believe, but also expectations that guide our beliefs without quite being part of them. We propose two ways of modelling the expectations used in nonmonotonic reasoning: by expectation sets, equipped with selection functions, and by expectation relations. For each of these we prove representation theorems and establish relations with several other modellings in the area, including Poole systems and preferential models.