Abstract This paper discusses the place of philosophical naturalism in the philosophy of law, with special reference to Scandinavian Realism. Hägerström originated a non-cognitivist analysis of certain fundamental legal concepts, but he also proposed an error theory. The two approaches are incompatible, but were not always clearly distinguished. Among his followers, Olivecrona and Ross gradually abandoned the latter, at least from the late 1940s. Many accounts of their views are unclear, because the presence of these two kinds of analysis, their incompatibility, and the gradual abandonment of one, has often been overlooked. A corollary of the discussion is that there are some important corrigenda in the entry “Naturalism in legal philosophy” in the Stanford Encyclopedia of Philosophy.