Deontic logic is concerned with the logical analysis of such normative notions as obligation, permission, right and prohibition. Although its origins lie in systematic legal and moral philosophy, deontic logic has begun to attract the interest of researchers in other areas, particularly computer science, management science and organisation theory. Among the application areas which have already received some attention in the literature are: issues of knowledge representation in the design of legal expert systems; the formal specification of aspects of computer systems, for instance in regard to security and access control policies, fault tolerance, and database integrity constraints; the formal characterisation of aspects of organisational structure, pertaining for example to the responsibilities and powers which agents are required or authorised to exercise. The “AEON” workshop proceedings provide some illustrations of work in these areas (see [ΔEON91; ΔEON94; ΔEON96]).

Deontic Logic and Contrary-to-Duties

We investigate under what conditions contrary-to-duty (CTD) structures lacking temporal and action elements can be given a coherent reading. We argue, contrary to some recent proposals, that CTD is not an instance of defeasible reasoning, and that methods of nonmonotonic logics are inadequate since they are unable to distinguish between defeasibility and violation of primary obligations. We propose a semantic framework based on the idea that primary and CTD obligations are obligations of different kinds: a CTD obligation pertains to, or pre-supposes, a certain context in which a primary obligation is already violated. This framework is presented initially as an extension of Standard Deontic Logic (SDL), a normal modal logic of type KD, and is illustrated by application to a series of examples. The concluding section is concerned with some resemblances between CTD and defeasible reasoning. We show first that the SDL-based framework contains a flaw and must be adjusted. A discussion of possible adjustments, including an alternative treatment in terms of a preference-based semantics, reveals difficulties that are reminiscent of problems in defeasible reasoning and intensional accounts of defeasible conditionals.

Contrary-to-duty obligations

One of the main issues in the discussion on standard deontic logic (SDL) is the representation of contrary-to-duty (CTD) obligations. A well-known example is Forrester’s (1984) paradox of the gentle murderer: it is forbidden to kill, but if one kills, one ought to kill gently.

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Dyadic Deontic Logic and Contrary-to-Duty Obligations

In this paper we discuss the role that deontic logic plays in the specification of information systems, either because constraints on the systems directly concern norms or, and even more importantly, system constraints are considered ideal but violable (so-called `soft? constraints).
To overcome the traditional problems with deontic logic (the so-called paradoxes), we first state the importance of distinguishing between ought-to-be and ought-to-do constraints and next focus on the most severe paradox, the so-called Chisholm paradox, involving contrary-to-duty norms. We present a multi-modal extension of standard deontic logic (SDL) to represent the ought-to-be version of the Chisholm set properly. For the ought-to-do variant we employ a reduction to dynamic logic, and show how the Chisholm set can be treated adequately in this setting. Finally we discuss a way of integrating both ought-to-be and ought-to-do reasoning, enabling one to draw conclusions from ought-to-be constraints to ought-to-do ones, and show by an example the use(fulness) of this.

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The role of deontic logic in the specification of information systems

https://dspace.library.uu.nl/bitstream/handle/1874/19964/broersen_04_action.pdf;sequence=1

R. Hilpinen

Papers

Actions in deontic logic