Some Key Notions in Non-monotonic Reasoning

This paper explores the role of some basic notions in the study of non-monotonic reasoning, such as validity, logical consequence, context, rules and assumptions. It offers some considerations about the relation between non-monotonicity and the ideal of perfect validity in logical inference and the pertinence of taking into account human limitations. I propose that work on non-monotonic reasoning can benefit from new notions of inference, logicality and reason. The paper is divided into three sections. The first section presents the motivations for this analysis and can be skipped by people familiar with non-monotonic reasoning. The second section offers a taxonomy of terms in the NMR literature. The third section proposes to expand the notion of logicality in three important ways.