Part I. Introduction. The Roman heritage -- Bonus theoreticus, malus practicus? -- What is the doctrinal study of law? -- Part II. The Foundations Of Legal Thinking. Lawyer's dilemma -- On language-games -- The foundations of knowledge -- On the ontology of law -- A moral point of view -- The three notions of liberty -- Part III. Between Realism And Idealism. What is science? -- Legal realism reinterpreted -- Outlines of the new rhetoric -- Scientific inference : an example -- Part IV. On The Doctrinal Study Of Law. From the constitutional state to the welfare state -- Two types of norms -- The formal validity, efficacy, and acceptability of legal norms -- The procedure of legal reasoning -- The sources of law -- One right answer? -- On the systematisation -- Change or development?