This article deals with the concept of truth -understood as alétheia, dis-closure- referred to the concept of Dasein (human being) used in Heidegger's work Being and Time. Anyway, to deal with this thought we must talk about openness or disclosedness (Erschlossenheit). The key idea Dasein is understood as "being there" or "being its there" (Da-sein), as highlighted the philosopher himself. Modes of the openness are circumspection (Umsicht) and looking-at (Hinsehen), as well as considerateness (Rücksicht) and forbearance (Nachsicht), inconsiderateness (Rücksichtslosigkeit) and perfunctoriness (Nachsehen). Viewed from another perspective, the there (Da) of Da-sein is constituted by understanding (Verstehen) as a project, a state-of-mind or mood (Befindlichkeit), and discourse or speech (Rede). These concepts are addressed together with resoluteness (Entschlossenheit), an eminent mode of openness.