The Fall explores Camus’s philosophy of the absurd. Most prominently, we see an illustration of Camus’s claim that all men are guilty of something. We are guilty not only by our actions, but by our inactions, or failure to act. Crimes we fail to stop are just as much our fault as those we commit ourselves. The novel explores several existential ideas as well, including Sartre’s "bad faith" and Kierkegaard’s "dread." The idea of doubt and universal uncertainty features not only in the novel’s themes, but in its technique and narration as well.
Jean-Baptiste’s discussion of Copernicus and "reverse reasoning" serves as advice on how to interpret The Fall.