The purpose of this chapter is to investigate the central fraction of deontic discourse that was dissected out in the previous chapter. In Section 10.1, the dominant approach to deontic logic, “standard deontic logic,” is shown to suffer from deficiencies that are closely related to its basic semantic construction. This motivates the search for another semantic construction in which these deficiencies can be avoided. In Secion 10.2, such a construction is proposed. It provides us with a set of prescriptive predicates with differing stringency. In Section 10.3, the logic of this construction is investigated, and in Section 10.4 a series of representation theorems is presented. In Sections 10.5 and 10.6, some more specified deontic predicates are constructed within the same framework, and their properties are investigated.

STANDARD DEONTIC LOGIC (SDL)

Modern deontic logic began with a seminal paper by Georg Henrik von Wright in 1951. With a minor modification, his list of postulates has turned out to be characterizable by a simple semantical construction that has long dominated the subject: It is assumed that there is a subset of the set of possible worlds (the “ideal worlds”) such that for any sentence p, Op holds if and only if p holds in all these worlds.