Karl Barth, who once was Harnack’s student and who was trained by liberals, knows that reduction formulas (i.e. reduction from the stranger to the familiar, from the unknown to the known, from the divine to the human) are diverse: ethical, historical, psychological. Guglielmo Forni Rosa therefore reminds us of some aspects of Harnack’s position that are crucial in order to understand Rousseau. Barth sees that referring to nature through reason or conscience creates an autonomous individual, free from the weight of authority; but rather than the Cartesian element of evidence, which is very important in Rousseau, he prefers to stress his stoical pre-Christian inspiration, that also constitutes the basis of the young Goethe’s thought. Indeed, he considers Rousseau as a man torn between two worlds: the Encyclopaedia and the Enlightenment on the one hand, and Goethe’s time and the early Romanticism (Schleiermacher’s On religion) on the other.