Early in being and Time Heidegger introduces a distinction between two modes of being (Seinsmodi) of Dasein, which he terms “authenticity” (Eigentlichkeit) and “inauthenticity” (Uneigentlichkeit). You exist in the mode of authenticity if you have “chosen, or achieved yourself in your being,” and you exist in the mode of inauthenticity if you have “lost or only seemingly achieved yourself” (SZ 42). In the course of Heidegger’s argument these notions take on an increasingly complex role in teasing out the basic concepts of human existence.