Jean-Paul Sartre (1905-1980) is both the author of these texts and—particularly in “Existentialism is a Humanism”—a character within them. Although Sartre began his career as an apolitical intellectual, he began to take an active and visible role in the public sphere toward the end of the Second World War (1944-45) and became the twentieth century’s public intellectual par excellence. His philosophical views placed him at odds with both Left and Right, and his pithy formulations of philosophical positions (as well as the popular press’s sensational misconstruals of those views) made him a controversial public figure. It is in this role that Sartre appears in “Existentialism is a Humanism,” attempting to defend his philosophy against the charges brought by philosophers and the public alike. 

René Descartes (1596-1650) was a French mathematician, philosopher, and scientist. His most famous philosophical work, the Meditations on First Philosophy (1641), is one of the key texts of modern Western philosophy. In it, Descartes employs the method of “radical doubt,” subjecting everything he believes to doubt in order to detect whether his body of putative knowledge contains any self-evident truths. The truth he alights on is what is now known as the cogito, the undeniable fact that if I am thinking, then I exist (“cogito, ergo sum”).