In everyday existence, Dasein typically understands itself not as an individual with a particular perspective and particular responsibilities but as das Man — the impersonal "one", the anonymous public self that thinks what one thinks, does what one does, interprets things as they are interpreted. This is not a failure or pathology; it is the necessary starting point from which every Dasein emerges and to which it always risks returning. Das Man is the average interpretation of existence: levelled down, made accessible, stripped of the burden of genuine individuality. It is comfortable precisely because it dissolves the weight of ownership.
Conscience calls Dasein back from its dispersal in das Man. The call is not a verbal message and has no specific content: it is a summons from the self to the self, calling Dasein toward its ownmost possibilities and out of its comfortable submersion in the they. What the call discloses is guilt (Schuld) — not moral guilt but the ontological structure of being-the-ground-of-a-nullity: Dasein finds itself thrown into possibilities it did not choose, and this thrownness is the permanent ground of its existence. To hear and heed the call is to be willing to have a conscience — to own one's nullity rather than evading it.
Authentic existence is not dramatic self-assertion or heroic isolation; it is resoluteness (Entschlossenheit) — a way of being-in-the-world in which Dasein faces its situation clearly, owns its thrownness, and acts from its ownmost understanding of its possibilities rather than from inherited convention or public opinion. Resoluteness is situationally specific: there is no general formula for authentic existence, no set of authentic attitudes one can adopt in advance. It is the mode in which Dasein, having heard the call of conscience, returns to the world with its eyes open.
The analysis of das Man and fallenness occupies §§25–27 and §35–38 of Being and Time. The call of conscience and resoluteness are developed in §§54–60. The concept of authenticity was enormously influential on Sartre, though Sartre's reading was significantly different from Heidegger's intention.
