Lecture 2: Kratzer, Poole, Conditionals and Means-End Reasoning ESSLLI’16: Deontic modality: linguistic and logical perspectives on oughts and ends

The formal framework introduced by Kratzer in 1981 is closely related to the work on DSDL in the sixties and seventies, such as the work of Hansson and Lewis discussed in the handout of Lecture 1. Her semantics is therefore sometimes referred to as the Lewis-Kratzer semantics. In the semantics of Kratzer, the preference ordering is not given, but it is constructed from two sets of propositions, called the modal base and the ordering source. The modal base gives the set of worlds of the preference ordering, namely the worlds satisfying all the sentences of the modal base. The ordering source gives the preference relation between the worlds, namely the subset ordering on the sentences of the ordering source. When the sentences of the ordering source are taken as obligations, this represents that a maximal number of obligations is fulfilled, or a minimal number of them is violated. Conditional obligations are then evaluated as in DSDL.