This article discusses the work of F. H. Jacobi – not so much the dispute concerning pantheism, but more particularly the quarrel of the Ancients and the Moderns. What does Jacobi mean when he asserts that modern philosophy pretends “to bring reason back to understanding” ? Jacobi follows the metamorphoses of reason linked to theological-political questions (Spinoza). Kant is the one who “enchained Proteus” and was confronted with the crisis of metaphysics that the conflict between faith (belief) and reason created. But, Kantian hermeneutics is based on a critical reinterpretation of Plato’s ideas which remains ambiguous and contradictory. According to Jacobi The Republic can help us to understand the situation in which Hobbes’ Leviathan and criticism originated. Far from presenting a Neo-Platonist system Jacobi insists on the Socratic attitude itself, on the Eros of reason to enlighten the aporia of idealistic reason that transforms platonic Ideas into ideals and human beings into Polyphems.