In this chapter, the author proposes the metaphysical aspects of vulnerability. All human being physically and existentially stands between life and death. This situation combines the three-dimensional human being: the existential pathos of "being in time" where we are vulnerable; the biological body and the interiority; and lately the capacity of the human subject. The conjunction of these three dimensions allows us to reach a deep ontological analysis of man and his life. This research includes an analysis of the Greek concept of "pathos' and the oversight of the "vulnerability" in the history of Philosophy. This way, the study demonstrates the importance of "being between life and death" and "being vulnerable" as a true and radical human essence. And so it offers an upgrade of bioethics research on a path towards a "Path-Ethics' and "Bio-philosophy".