 A phenomenology of consciousness, then, explores neither the metaphysical composition nor the causal genesis of things, but the “constitution” of their meaning. Husserl employed this method to clarify our experience of nature, the socio-cultural world, logic, and mathematics, but Heidegger argued that he had failed to raise the most fundamental question, that of the “meaning of being” as such. In turning phenomenology toward the question of what it means to be, Heidegger insists that the question be raised concretely: it is not at first some academic exercise but a burning concern arising from life itself: the question of what it means for me to be. Existential themes take on salience when one sees that the general question of the meaning of being involves first becoming clear about one’s own being as an inquirer. According to Heidegger, the categories bequeathed by the philosophical tradition for understanding a being who can question his or her being are insufficient: traditional concepts of a substance decked out with reason, or of a subject blessed with self-consciousness, misconstrue our fundamental character,  “being-in-the-world.” In his phenomenological pursuit of the categories that govern being-in-the-world, Heidegger became the reluctant father of existentialism because he drew inspiration from two seminal, though in academic circles then relatively unknown, nineteenth-century writers, Søren Kierkegaard and Friedrich Nietzsche. One can find anticipations of existential thought in many places (for instance, in Socratic irony, Augustine, Pascal, or the late Schelling), but the roots of the problem of existence in its contemporary significance lie in the work of Kierkegaard and Nietzsche.