We discuss the meaning of "being alive" and "being dead." Our primary aim is to pave the way for a sound and accurate ethical debate concerning these two concepts. In particular, we analyze a metabolic approach and a genetic one and discuss the reasons for their failure to constitute a good starting point for successive debates. We argue that any ethical or social discussion of topics involving life and death must introduce cultural constructs such as, on the one hand, the concept of clinical death and, on the other hand, the concept of existence. We argue that these two cultural constructs, although consistent with biomedical knowledge, cannot be ontologically grounded in it. To conclude, we apply our findings to the case of human embryos.