The French sociologist Raymond Aron himself felt that his reflections on the conditions of political action, a topic dealt with in his Introduction à la philosophie de l'histoire, became the basis for his own political involvement. In the book, the problem of action is closely linked to an analysis of man's relationship to history, an analysis that explores the issue of man's ability to know his past and present. This article looks at Aron's attempt to overcome the scepticism of historical relativism, and to regain objectivity. Before explaining this process the author attempts to place the book in its proper historical and intellectual context, and he then reveals how its theme of human action is linked to Aron's epis-temology. According to Aron, choice, action and decision are the three main concepts and requisites positively linked with man's relationship to history. After explaining their relevance, the author shows how Aron uses them to overcome historical relativism and scepticism. This solution is then confronted with the issue of the other, not really elaborated by Aron, and discussed in the light of postmodern thought. The article closes with a look at the question of Aron's existentialism, as his Introduction is often said to resemble Sartre's philosophy.