In this paper we describe an algorithmic framework for a multi-modal logic arising from the combination of the system of modal (epistemic) logic devised by Meyer and van der Hoek for dealing with nonmonotonic reasoning with a deontic logic of the Jones and Pörn-type. The idea behind this (somewhat eclectic) formal set-up is to have a modal framework expressive enough to model certain kinds of deontic defeasibility, in particular by taking into account preferences on norms. The appropriate inference mechanism is provided by a tableau-like modal theorem proving system which supports a proof method closely related to the semantics of modal operators. We argue that this system is particularly well-suited for mechanizing nonmonotonic forms of inference in a monotonic multi-modal setting.

This paper presents a deontic logic Σ for reasoning about permission or prohibition to know some parts of the database content in the context of a multilevel confidentiality policy. The most important logical features in the definition of a multi-level policy are that each confidentiality level is defined by a set of sentences and that, when the policy is designed, the permission to know is not necessarily the complement of the prohibition to know. These concepts are formalized in a modal logic where deontic modalities, doxastic modalities and confidentiality levels are interpreted by non-standard modal models. The corresponding axiomatics is also presented in the paper and its soundness and completeness have been proved. A limitation of the Σ logic is that sentences in the scope of modalities are sentences of Propositional Calculus. Finally, it is shown how the logic can be used to express constraints to guarantee the consistency of a policy or to prevent the existence of inference channels. That is, the possibility to infer sentences that are not permitted to know from other sentences that are permitted to know. Both deductive and abductive channels are considered.

Keywords: deon96

In this paper we propose a semantics for dyadic deontic logic with an explicit preference ordering between worlds, representing different degrees of ideality. We argue that this ideality ordering can be used in two ways to evaluate formulas, which we call ordering and minimizing. Ordering uses all preference relations between worlds, whereas minimizing uses the most preferred worlds only. We show that ordering corresponds to strengthening of the antecedent, and minimizing to weakening of the consequent. Moreover, we show that in some cases ordering and minimizing have to be combined to obtain certain desirable conclusions, and that this can only be done in a so-called two-phase deontic logic. In the first phase, the preference ordering is constructed, and in the second phase the ordering is used for minimization. If these two phases are not distinguished, then counterintuitive conclusions follow.

Keywords: deon96

In this paper a new action concept is proposed, within the same tradition of the logical characterization of act descriptions as employed by Kanger, Pörn and Lindahl. The concept sums up a successful goal oriented social activity into a unique assertion referring to the agent who has initiated it. It is argued that this notion allows us to increase the expressiveness of the characterization of agents' activity within organizations. For describing the agents' interaction the normative systems perspective is adopted, viewing such interactions as governed by norms and expressing them in terms of what agents are premitted and obliged to do. In this context, the new concept allows us to cope with normative descriptions that play an important role in organizations: responsibilities. The minima properties of this “indirect" agency operator are discussed, and an “influence" operator is also introduced in order to cope with interactions between the different agents. The interest of these concepts within the analysis and specification of organizations is illustrated.

Keywords: deon96

The last few years several defeasible deontic reasoning formalisms are developed as a way to solve the problem of deontic inconsistency. However, these formalisms are unable to deal with some very common forms of deontic reasoning, since e.g. their expressiveness is restricted. In this paper we will establish a priority hierarchy of legal rules to solve the problem of deontic conflucts and we will give a mechanism to reason about nonmonotonicity of legal rules over the priority hierarchy. The theory presented here, based on defaylt logic and a modification and extension of the argumentation framework of Prakken, properly deals with some shortcomings of other defeasible deontic reasoning approaches.

Keywords: deon96

The contribution of this paper lies in the analysis of the relationship between impersonal and personal deontic notions, keeping them as close to standard deontic logic as possible. In doing so, we offer arguments against reducing both personal notions to impersonal notions, and impersonal notions to personal notions. We discover that we need to introduce two new notions of impersonal obligation and permission. Finally we argue in favour of one particular representation of ought-to-do and permitted-to-do statements.

Keywords: deon96

Some key pre-theoretic semantic and pragmatic phenomena that support a negative answer to the main title question are identified and a conclusion of some significance is drawn: a pervasive bipartisan presupposition of twentieth century ethical theory and deontic logic is false. Next, an intuitive model-theoretic framework for "must" and "ought" is hypothesized. It is then shown how this hypothesis helps to explain and predict all the pre-theoretic phenomena previously observed. Next, I show that the framework hypothesized possesses additional expressive and explanatory power, thus adding further confirmation that it is on the right track.

Keywords: deon96

This paper exploits the properties of adjointness to develop a theory of norms. The adjoints are a pair of mappings between two logics, one called IMP, a logic of imperatives, and another called PROP, which is ordinary logic. In particular, L is a mapping from PROP to IMP and it has a right adjoint R from IMP to PROP. Norms are defined, formally, as statements that contain occurrences of RU where U is in IMP. A simple theorem (reminiscent of Kant's “ought implies can"): Responsibility implies power and, moreover, incapacity implies immunity.

Keywords: deon96

The paper of this paper is to explore a new deontic operator for representing what an agent ought to do; the operator is cast against the background of a modal treatment of action developed by Nuel Belnap and Michael Perloff, which itself relies on Arthur Prior's indeterministic tense logic. The analysis developed here of what an agent ought to do is based on a dominance ordering adapted from the decision theoretic study of choice under uncertainty to the present account of action. It is shown that this analysis gives rise to a normal deontic operator, and that the result is superior to an analysis that identifies what an agent ought to do with what it ought to be that the agent does.

Keywords: deon96

This paper investigates diachronic deontic logic, based on models with forward-branching time. Using such models, supplemented by a choice function to model human agancy, and an obligation function to introduce normative features, it is possible to develop a rich language with tense logic, since and untill operators, and operators expressing action, ability, and obligation. It then becomes possible to model, not only the interrelationships among our obligations, but also their interrelationships with the actions which give rise to them, the actions which fulfill them, and the abilities these actions require.

Keywords: deon96

In this paper we introduce some new operators into our framework that make it possible to reason about decisions and commitments to do actions. In our framework, a decision leads to an intention to do an action. The decision in itself does not change the state of the world, but only the relation to possible future worlds. A commitment to actually perform the intended action changes the deontic state of the world such that the intended action becomes obligated. Of course, the obligated action may never actually occur. In our semantic structure, we use static (ought-to-be) and dynamic (ought-to-do) obligation operators. The static operator resembles the classical conception of obligation as truth in ideal worlds, wxcept that it takes the current state as well as the past history of the world into account. This is necessary because it allows us to compare the way a state is actually reached with the way we committed ourselves to reach it. We show that some situations that could formerly not be expressed easily in deontic logic can be described in a natural way using the extended logic described in this paper.

Keywords: deon96

The Hohfeldian fundamental legal conceptions that deal with solely deontic LEGAL RELATIONS, the duty/privilege and right/no-right pairs, require not only an adequate definition of agency for the person who is obligated or permitted to act, but also the same of patiency for the person to-or-for whom that action is directed. Person-i's DUTY to see-to-it-that that state-of-affairs-s is so for the benefit of person-j is defined here in terms of a deontic OBLIGATION operation and DONE-BY (D2) and DONE-FOR (D4) relations between a state of affairs and persons. This paper is a refinement of hte author's earlier efforts to modify, extend, and enrich Hohfeld's fundamental legal conceptions into a more general notion of LEGAL RELATIONS (defined concepts are expressed in capital letters.) In particular, the agency concept DONE-BY is being brought into closer conformity with Belnap's emerging stit logic, with the modifications of deontic logic accompanying such changes. The S4-D2 action modal logic considered here is intended to be part of the A-HOHFELD logic in which LEGAL RELATIONS are defined and from which a representation language called the A-HOHFELD language is derived. The A-HOHFELD language is being used as a representation language for constructing MINT (Multiple INTerpretation) interpretation-assistance system for helping lawyers to detect alternative structural interpretations of sets of legal rules.

Keywords: deon96

Keywords: deon96