Norm and Nature: The Movements of Legal Thought, by Roger Shiner, is an intricate book with the perhaps surprising thesis that the outstanding problem in legal philosophy, the conflict between positivism and natural law, is irresolvable. The controversy is doomed to a never-ending cycle because “sophisticated positivism follows from positivism's difficulties with simple positivism … anti-positivism follows from sophisticated positivism's difficulties with simple positivism; [and] simple positivism follows from positivism's difficulties with anti-positivism” (p. 281). For legal theory, then, an understanding of law is simply an understanding of why legal theory is thus “condemned to endless dialectic” (p. 324). And the reason is found in the nature of law itself and the perennial tension between, on the one hand, certainty and procedure and, on the other, flexibility and substance.