Chapter 1: Introduction (Peter Langford, Ian Bryan and John McGarry) -- Part I: Legal Science Before The Tribunal Of Validity.-Chapter 2: Hans Kelsen and the Social Fact Thesis (Lorenz Kähler).-Chapter 3: Natural Law and the Nature of Law: Kelsen’s Paradox (Pierre-Yves Quiviger) -- Part II: Beyond Natural Law? -- Chapter 4: Natural Law Systematics: Is There a ‘Grundnorm’ in Natural Law? …