There is much talk in this paper about “contraries”, sometimes creative contraries that have contributed to the progress of thought, but also about contraries that produce only error and confusion, such as those due to certain advocates of historical psychology. We present in this paper some applications to philosophical texts of a method of interpretation, which consists in putting them back into the context of the teaching and life specific to philosophical schools. In addition to the meticulous studies devoted to important philosophical terms, the present volume also contains several general contributions, which have become justly famous, devoted to the sections of philosophy, the organization of teaching in philosophical schools, the distribution of disciplines and, last but not least, the figure of the sage. Pierre Hadot’s research deals first with the relationship between Hellenism and Christianity, then with Neoplatonic mysticism and Hellenistic philosophy, and finally with philosophy as a spiritual phenomenon.