In 2016, the Oxford Dictionary named “post-truth” the word of the year. In the ongoing debate about post-truth it is generally assumed that facts and truth have ceased to be relevant to politics. However, questions are seldom raised about the role of truth-claims in politics, why facts matter in political contexts, or what we even mean with words such as fact and lies in politics. A general aim of the present study is to shed light on these questions. Not, however, (...) by engaging directly in the debate about post-truth, but by investigating the relation between politics and truth in the philosophical work of Hannah Arendt and Martin Heidegger. In 1945 Arendt suggested that fascism had invented a way of “lying the truth”. She later came to call this invention the modern political lie, seeing it as one of the key elements that crystallized into totalitarianism. The study explores the paradoxical relation between politics and truth in totalitarian movements, which can reinvent itself in non-totalitarian forms in contemporary democracies. Parts of Arendt’s analysis are implicit but can be made explicit against the background of Heidegger’s political writings. Heidegger is not an advocate of the modern political lie, nonetheless his writings from the 1930s, while a member of the National Socialist party, reflect aspects of the paradoxical relation between politics and truth in totalitarian movements. Studying Heidegger and Arendt together can therefore shed light on the specific problems that Arendt addressed regarding truth and lying in politics. The study investigates the relation between politics and truth in Heidegger and Arendt respectively, but also the relation between their works. It shows that there is a proto-political aspect already in Heidegger’s early articulations of truth as aletheia and explores the central role of truth in his political writings from the 1930s. Against the background of Heidegger, Arendt’s works on the modern political lie are analyzed. The study also investigates the concept of truth developed by Arendt in works after The Origins of Totalitarianism, arguing that it should be seen partly as a response to the modern political lie. (shrink)