Jean-Paul Sartre claims in his 1945 lecture "Existentialism is a Humanism" that there are two kinds of existentialism: that of Christians like Karl Jaspers, and atheistic like Martin Heidegger. Sartre's "spiritual master" Heidegger had no problem with Sartre defining him as an atheist, but he had serious problems with Sartre's concept of humanism and existentialism. Heidegger claims that the essence of humanism lies in the essence of the human being. After the Enlightenment, the Western concept of man has been presented in education in the form of Kantian humanistic essentialism. At least in the Finnish educational system, Kantian humanism is almost an official ideological background of all national curriculums. Is such a kind of essentialism and metaphysics plausible in our modern or postmodern times? We examine the Sartre-Heidegger controversy on humanism and the concept of man in education using Freire's humanism and Gelassenheit education as exemplars.