Deontic Reasoning on the Basis of Consistency Considerations Christian Straßer ∗ Aleks Knoks † Joke Meheus ∗ ∗ Ghent University † University of Maryland February 10, 2014 Abstract Deontic conflicts pose an important challenge to deontic logicians. The standard account —standard deontic logic, SDL— is not apt for address- ing this challenge since it trivializes conflicts. Two main stratagems for gaining conflict-tolerance have been proposed: to weaken SDL in various ways, and to contextualize the reign of SDL to consistent subsets of the premise set. The latter began with the work of van Fraassen and has been further developed by Horty. In this paper we characterize this second ap- proach in general terms. We also study three basic ways to contextualize SDL and supplement each of these with a dynamic proof theory in the framework of adaptive logics. Keywords: deontic conflicts; maximal consistent subsets; adaptive log- ics; nonmonotonic logic; conflict-tolerance; 1 Introduction One of the major challenges for the deontic logic community is the handling of deontic conflicts. A deontic conflict occurs in a situation in which an agent faces conflicting norms. For instance, our agent may have made two promises: one – to finish and send off a review this evening, and another – to take out his spouse for a romantic dinner. However, it is impossible to fulfill the corresponding obligations to keep both promises. Let us write OA for an obligation to bring about A. Each of the following principles may be considered a good candidate for a fundamental principle of deontic reasoning (see [11]): Agg OA and OB imply O(A ∧ B) Inh If A classically implies B then OA implies OB D OA implies ¬O¬A And, indeed, the three inference types are valid in standard deontic logic (hence- forth – SDL). 1 However, with these three principles we run into a serious com- 1 We present the full axiomatization of SDL in Section 2. 1