Raymond Aron is the greatest figure in French liberalism of the twentieth century. In the tradition of Montesquieu, Constant, Tocqueville, and Elie Halévy, he is part of the French school of political sociology, which he defined in his Les Etapes de la pensée sociologique: "This is mostly a non-dogmatic school of sociologists, primarily interested in politics, who, without ignoring the social infrastructure, respect the autonomy of the political order and think as liberals." His liberalism, his lucidity in the face of the upheavals of that period, and his posture as a committed observer anxious to ensure consistency among his thoughts, words, and deeds, give him a unique place among French intellectuals, distinguishing him both from his masters—such as Alain, Léon Brunschvicg, and Célestin Bougie— and his contemporaries—-Jean-Paul Sartre, Nizan, and Simone Weil.