Crítica, Revista Hispanoamericana de Filosofía, Volume 19, number 55, abril 1987
Sobre a lógica deôntica não-clássica
[Sobre una lógica deóntica no clásica]
Leila Z. Puga
Universidad Católica de Sao Paulo

Newton C.A. da Costa
Universidad de Sao Paulo


Our starting point, in this basically expository paper, is the study of a classical system of deontic propositional logic, classical in the sense that it constitutes an extension of the classical propositional calculus. It is noted, then, that the system excludes ab initio the possibility of the existence of real moral dilemmas (contradictory obligations and prohibitions), and also can not cope smoothly with the so-called prima facie moral dilemmas. So, we develop a non-classical, paraconsistent system of propositional deontic logic which is compatible with such dilemmas, real or prima facie. In our paraconsistent system one can handle them neatly, in particular one can directly investigate their force, operational meaning, and the most important consequences of their acceptance as not uncommon moral facts.

Of course, we are conscious that other procedures for dealing with them are at hand, for example by the weakening of the specific deontic axioms. It is not argued that our procedure is the best, at least as regards the present state of the issue. We think only that owing, among other reasons, to the circumstance that the basic ethical concepts are intrinsically vague, it seems quite difficult to get rid of moral dilemmas and of moral deadlocks in general. Apparently this speaks in favour of a paraconsistent approach to ethics. At any rate, a final appraisal of the possible solutions to the problem of dilemmas and deadlocks, if there is one, constitutes a matter of ethical theory and not only of logic. On the other hand, the paraconsistency stance looks likely to be relevant also in the field of legal logic.

It is shown, in outline, that the systems considered are sound and complete, relative to a natural semantics. All results of this paper can be extended to first-order and to higher-order logics. Such extensions give rise to the question of the transparency (or oppacity) of the deontic contexts. As we shall argue in forthcoming articles, they normally are transparent.

[L.Z.P., N.C.A. da C.] (PDF en portugués)


| PDF en Spanish (175 Kb)