This essay critically engages Dreyfus's widely read interpretation of Heidegger's Being and Time . It argues that Dreyfus's reading is rooted in two primary claims or interpretative principles. The first - the Cartesianism thesis - indicates that Heidegger's objective in Being and Time is to overturn Cartesianism. The second - the hermeneutics of suspicion thesis - claims that Division II is supposed to suspect and throw into question the results of the Division I analysis. These theses contribute to the view that there are two conflicting accounts of inauthenticity that threaten the coherence of Heidegger's notion of authenticity. This view concerning authenticity is mistaken, as are the two theses that support it. The first thesis is incorrect because Heidegger's explicit aim is to investigate the question of the meaning of being not to overturn Cartesianism. The second is incorrect because the analyses of Division I describe the structures of everyday human existence in preparation for a closer examination in Division II of what makes them possible. Division II does not undercut Division I; it carries the analysis deeper. Authenticity, then, is not a negation of everydayness; it is a deepening of the self-understanding expressed in everydayness.