 The “naturalistic turn” that has swept so many areas of philosophy over the past five decades has also had an impact in legal philosophy. There are various forms of philosophical naturalism, all of which have influenced legal philosophy to different extents. Methodological naturalists (M-naturalists) view philosophy as continuous with empirical inquiry in the sciences. Some M-naturalists want to replace conceptual and justificatory theories with empirical and descriptive theories; they take their inspiration from more-or-less Quinean arguments against conceptual analysis and foundationalist programs. Other M-naturalists retain the normative and regulative ambitions of traditional philosophy, but emphasize that it is an empirical question what normative advice is actually useable and effective for creatures like us. Some M-naturalists are also substantive naturalists (S-naturalists). Ontological S-naturalism is the view that there exist only natural or physical things; semantic S-naturalism is the view that a suitable philosophical analysis of any concept must show it to be amenable to empirical inquiry.