Article

Minds and Machines

, Volume 21, Issue 3, pp 411-430

First online:

NO Revision and NO Contraction

  • Gregory WheelerAffiliated withCENTRIA—Artificial Intelligence Center, Department of Computer Science, Universidade Nova de Lisboa, FCT/UNL
  • , Marco AlbertiAffiliated withCENTRIA—Artificial Intelligence Center, Department of Computer Science, Universidade Nova de Lisboa, FCT/UNL Email author 

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Abstract

One goal of normative multi-agent system theory is to formulate principles for normative system change that maintain the rule-like structure of norms and preserve links between norms and individual agent obligations. A central question raised by this problem is whether there is a framework for norm change that is at once specific enough to capture this rule-like behavior of norms, yet general enough to support a full battery of norm and obligation change operators. In this paper we propose an answer to this question by developing a bimodal logic for norms and obligations called NO. A key to our approach is that norms are treated as propositional formulas, and we provide some independent reasons for adopting this stance. Then we define norm change operations for a wide class of modal systems, including the class of NO systems, by constructing a class of modal revision operators that satisfy all the AGM postulates for revision, and constructing a class of modal contraction operators that satisfy all the AGM postulates for contraction. More generally, our approach yields an easily extendable framework within which to work out principles for a theory of normative system change.

Keywords

Norms Modal logic Revision Contraction