Contextual Reasoning: Usually Birds Can Abductively Fly

Abstract

We present a new logic programming approach to contextual reasoning, based on the Weak Completion Semantics (WCS), the latter of which has been successfully applied in the past to adequately model various human reasoning tasks. One of the properties of WCS is the open world assumption with respect to undefined atoms. This is a characteristic that is different to other common Logic Programming semantics, a property that seems suitable when modeling human reasoning. Notwithstanding, we have noticed that the famous Tweety default reasoning example, originally introduced by Reiter, cannot be modeled straightforwardly under WCS. Hence, to address the issue and taking Pereira and Pinto’s inspection points as inspiration, we develop a notion of contextual reasoning for which we introduce contextual logic programs. We reconsider the formal properties of WCS with respect to these and verify whether they still hold. Finally, we set forth contextual abduction and show that not only the original Tweety example can be nicely modeled within the new approach, but more sophisticated examples as well, where context plays an important role.