This paper challenges Levinas's thesis that it is necessary to escape Heidegger's fundamental ontology in order to think ethically. It discusses how Levinas thinks the ethical relationship in Otherwise than Being, as "substitution," as "responsibility for the responsibility of the other," and it shows that one's responsibility for the other's responsibility can also be interpreted existentially, as authentic Fürsorge, as care for the other's care. The "substitution of one for the other" and the "care for the other" are indeed different, but not antithetical. Firstly, Dasein's authentic existentiell understanding of the other does not reduce him to "the same", because it does not "reduce" him to the apriori structures of Dasein. Secondly, the equiprimordiality of "Being-with" (Mitsein) and "Dasein-with" (Mitdasein) – in short, Mitt(da)sein – indicates the exposure of one to the other within the factical modes of Being-with-one-another and, therefore, the indebtedness of one to the other for one's potentiality-for-Being. Consequently, Dasein's assumed responsibility or authentic care for its potentiality-for-Being is not ego(t)istic, as Levinas contends, but entails caring for the other's Being, for his unique otherness.