Abstract

Deontic logic is a branch of logic that investigates normative concepts, systems of norms and normative reasoning. The formal languages of deontic logic include normative concepts that correspond to natural language notions such as ought, obligatory, permissible, forbidden and optional. The present book is an introduction to this branch of logic. Several basic deontic systems are described and some of their properties are explored. Every system is characterized both semantically using possible world semantics and axiomatically. The final chapter includes soundness and completeness results for every system. The focus of the study is formal, but some philosophical questions are also raised, in particular: What is the meaning of the word "ought" and other normative notions as they occur in ordinary and philosophical discussions? Several distinctions between different kinds of obligations are considered, for instance the distinctions between prima facie and all things considered obligations and between conditional and unconditional obligations. The book is aimed at people with no prior knowledge of deontic logic but with some acquaintance with classical logic including some set theory. It should interest anyone who wants to know more about this area.