The relationship between Raymond Aron and Immanuel Kant is both obvious and controversial. We all know that his master's thesis in philosophy (1928) was devoted to "Intemporality in Kant" and his first philosophical position was that of a neo-Kantian, inspired by his teacher Brunschvicg. We also know that after the 1930s, with the shock of his discovery of Germany and the rise of Nazism, he devoted his life to reflection and action, both objective and nuanced, on the one hand, and engaged and passionate on the other, in politics. Everyone can see that references to Kant often appeared in his writings, most notably the concept of the "idea of Reason."