Paul concentrates his research in ethical theory, deontic logic, and the philosophy of moral language. He is best known for his work in deontic logic—having authored (or co-authored) book-length overviews of deontic logic (in the _Stanford Encyclopedia of Philosophy_, in the _Handbook of the History of Logic, vol. 7: Logic and the Modalities in the Twentieth Century_, and in the _Handbook of Deontic Logic and Normative Systems, Vol 1_) and, in particular, for a number of formal articles where he identifies logical schemes that make room for supererogation and other concepts of common sense morality, as well as informal ethical theory articles on the same topic. Some of his work and that of others in this area is summarized in his entry “Logics for Supererogation and Allied Normative Concepts” in the _Handbook of Deontic Logic and Normative Systems, Vol.2_. He was a fellow at the Institute of Philosophy, School of Advanced Studies, University of London, oversees the Northern New England Philosophical Association, and serves on the steering committees for the DEON conference series, and for the newer Formal Ethics conference series.