Trial by Slogan: Natural Law and Lex Iniusta Non Est Lex

Norman Kretzmann's recent analysis of the natural lawslogan ``lex iniusta non est lex' (an unjust law is nota law) demonstrates the coherence of the slogan andmakes a case for its practical value, but I shallargue that it also ends up showing that the sloganfails to mark any interesting conceptual or practicaldivision between natural law and legal positivistviews about the nature of law. I argue that this is ahappy result. The non-est-lex slogan has been used toexaggerate the extent of disagreement about the natureof law and has diverted critics of natural law theoryfrom recognizing that the main disagreement betweennatural lawyers and legal positivists centres ontheories of practical reason and how they affect ourunderstanding of the relationship between law andmorality. This extends the debate about the nature oflaw somewhat beyond the traditional boundaries ofphilosophy of law, but these boundaries are due inpart to the diversion created by debate over thenon-est-lex slogan. Recognizing that the non-est-lexslogan fails on its own to mark any interestingpractical or conceptual division between natural lawtheories and legal positivism should therefore focusand encourage debate on matters of genuine substancebetween these outlooks. The disagreement, however, mayturn out to be primarily metaphysical and explanatoryand not normative in nature.