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Henning Herrestad, Formal Theories of Rights, Oslo: Juristforbundets Forlag, 1995. 295pp. ISBN 82-7833-014-8.
1. Introduction. Why AI &Law Needs a Formal Theory of Rights
One of the most debated issues of AI &law is that concerning the use of a deontic logic in the representation of legal knowledge (Herrestad, 1990). In earlier times two opposed positions seemed to be clearly distinguishable. Some authors contested the use of deontic logic in most (if not in all) applications of computers to the law (Kowalski, 1989; Bench-Capon, 1989), or suggested to resort to an elementary deontic logic, limited substantially to the reciprocal definition of "obligatory" and "permitted" (cf. Biagioli et al., 1989). Others, on the contrary, affirmed that AI & law requires a fully developed deontic logic (cf. McCarty, 1986; Allen and Saxon, 1986), although possibly disagreeing on what requirement such a logic should meet.
The first position could be supported by both an empirical argument and a theoretical one.
The empirical argument is grounded on the fact that almost all legal information systems (whether or not they use AI techniques) do not include any representation of deontic notions. Although some systems have adopted a deontic terminology, their logical treatment of deontic terms is usually so elementary that it cannot be qualified as a deontic logic proper. Correspondingly, some researchers interested in practical application have explicitly rejected deontic logic. Others have only paid lip service to it. For example, Susskind (1987, 228 ss) after emphasising the necessity of deontic logic, considers "ought" as consisting in the link between legal conditions and legal effects (in the spirit of the Kelsenian Sollen), and therefore reduces it to a conditional connective.
The theoretical argument is based on the uncertainties that still characterise deontic logic, more than forty years after its putative birth (von Wright, 1951). Deontic logic has adopted sophisticated formalisms and has been applied to many legal and moral contexts, but still appears to lack solid logical and philosophical foundations, and continues to spawn (more or less) disquieting paradoxes.
The opposite position - to wit the thesis of the need for a developed deontic logic - could instead be supported by pointing to the intuitive appropriateness of deontic notions and to the possible theoretical developments that they allow.
It was...