this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based

ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus prof.dr. D.C. van den Boom ten overstaan van een door het college voor promoties ingestelde commissie, in het openbaar te verdedigen in de Aula der Universiteit op dinsdag 26 februari 2008, te 12.00 uur door

In this paper we introduce a multi agent deontic update semantics, that builds on a logic of prescriptive obligations (norms) and a logic of descriptive obligations (normative propositions) . In this preference-based logic we formalize rights as a new type of strong prescriptive permissions and duties and commitments as prescriptive obligations between agents. 1 Introduction In groups of agents there is a fundamental dierence between an agent creating an obligation or permission for another agent and an agent evaluating whether such deontic states hold, because the former is an act whereas the latter is an assessment. For example, a purchase contract creates an obligation for the buyer to pay the seller for the goods, when buying a CD via the Internet the buyer can grant permission to the merchant to charge his credit card by sending his card number, and the city counsel can grant a permission to a person to build a house. Usually deontic states are created by performing cert...

Abstract. If we are to take the notion of speech act seriously, we must be able to treat speech acts as acts. In this paper, we will try to model changes brought about by various acts of commanding in terms of a variant of update logic. We will combine a multi-agent variant of the language of monadic deontic logic with a dynamic language to talk about the situations before and after the issuance of commands, and the commands that link those situations. Although the resulting logic inherits various inadequacies from monadic deontic logic, some interesting principles are captured and seen to be valid nonetheless. A complete axiomatization and some interesting valid principles together with concrete examples will be presented, and suggestions for further research will be made. 1

. In this paper we introduce Prohairetic Deontic Logic (PDL), a preference-based dyadic deontic logic. An obligation `ff should be (done) if fi is (done)' is true if (1) no :fffi state is as preferable as an fffi state and (2) the preferred fi states are ff states. We show that the different elements of this mixed representation solve different problems of deontic logic. The first part of the definition is used to formalize contrary-to-duty reasoning, that for example occurs in Chisholm's and Forrester's notorious paradoxes. The second part is used to make dilemmas inconsistent. PDL shares the intuitive semantics of preference-based deontic logics without introducing additional semantic machinery such as bi-ordering semantics or ceteris paribus preferences. 1 Introduction Deontic logic is a modal logic, in which absolute and conditional obligations are represented by the modal formulas Off and O(ffjfi), where the latter is read as `ff ought to be (done) if fi is (done).' It can be use...

. In this article we introduce Contextual Deontic Logic (Cdl) to analyze the relation between deontic, contextual and defeasible reasoning. The optimal state, and therefore the set of active obligations, can change radically when the violation context changes. In such cases we say that the obligations only in force in the previous violation context are defeated; contextual deontic logic is therefore a defeasible deontic logic. This is expressed by the definition O fl (ffjfi) =def O(ffjfin:fl): `ff ought to be (done) if fi is (done) in the context where fl is (done)' is defined as `ff ought to be (done) if fi is (done) unless :fl is (done).' The unless clause formalizes explicit exceptions and is analogous to the justification in Reiter's default rules. Cdl is a monotonic defeasible deontic logic, because it has factual defeasibility but not overridden defeasibility. 1. Introduction It is well-known in deontic logic that there are striking similarities between deontic reasoning and c...

The deontic logic dus is a deontic update semantics for prescriptive obligations based on the update semantics of Veltman. In dus the definition of logical validity of obligations is not based on static truth values but on dynamic action transitions. In this paper prescriptive prima facie obligations are formalized in update semantics. The logic formalizes the specificity principle, has reinstatement and does not have an irrelevance problem. Moreover, it handles the diagnostic problem by distinguishing

. In this paper we discuss the role of context and independence in normative reasoning. First, deontic operators -- obligations, prohibitions, permissions -- referring to the ideal context may conflict with operators referring to a violation (or contrary-to-duty) context. Second, deontic independence is a powerful concept to derive deontic operators from such operators of other violation contexts. These two concepts are used to determine how to proceed once a norm has been violated, a key issue of deontic logic applications in computer science. We also show how violation contexts and deontic independence can be used to give a new analysis of several notorious paradoxes of deontic logic. 1 Introduction Deontic logic is a modal logic in which flp is read as `p ought to be (done),' Fp as `p is forbidden to be (done)' and Pp as `p is permitted to be (done).' Deontic logic has traditionally been used by philosophers to analyze the structure of the normative use of language. In the eightie...

Abstract. Obligation change raises the "frame problem " which is to characterise what obligations remain unchanged after an action has been performed. Many general solutions have been proposed but even if they are attractive from a thoretical point of view they have practical drawbacks. In this paper simple solutions are proposed thanks to the restriction to obligations that take the form of modal literals. These solutions are presented in the framework of dependence logic and of situation calculus, and it is shown that they are based on the same intuitive idea. This idea is to express that we have a complete representation of actions and circumstances that can change an obligation. 1 Introduction The problem of the characterisation of what remains to be true after the per-formance of an action is recognised as a difficult problem in the field of Articial Intelligence. This problem is usually called the "frame problem".The same problem arises in the field of deontic logic if we want to characterise the set of obligations that persist after an action. It has some connections withdeontic defeasibility but it is not the same problem (see [10, 1, 12, 9, 17]). An interesting solution to the frame problem has been proposed by Reiter [11]in the framework of situation calculus for modelling the evolution of the world. Later on this solution has been extended to the evolution of beliefs about theworld by Scherl and Levesque [16, 14]. This work has been extended to revision by Shapiro et al. in [15]. In [4] Demolombe has adapted their intuitive ideasto the evolution of obligations. However, this solution has practical drawbacks because it requires to assign to all the ideal situations an ideality level in thesame way as Scherl and Levesque require the assignement of a plausibility level.

Dynamic logic, broadly conceived, is the logic that analyses change by decomposing actions into their basic building blocks and by describing the results of performing actions in given states of the world. The actions studied by dynamic logic can be of various kinds: actions on the memory state of a computer, actions of a moving robot in a closed world, interactions between cognitive agents performing given communication protocols, actions that change the common ground between speaker and hearer in a conversation, actions that change the contextually available referents in a conversation, and so on. In each of these application areas, dynamic logics can be used to model the states involved and the transitions that occur between them. Dynamic logic is a tool for both state description and action description. Formulae describe states, while actions or programs express state change. The levels of state descriptions and transition characterisations are connected by suitable operations that allow reasoning about pre- and postconditions of particular changes.