Upon the reformulation of subjectivity, this chapter discusses how the plurality of subjects is irreducible. For some philosophies, the plurality of subjects is like a scandal: it is introduced only to remedy the deficiencies which the singular subject happens to exhibit, while ideally there can be but one subject. By contrast, one of the advantages of the ontology of temporal differentiation is its justification of plurality. First, openness to the other is found at the heart of subjectivity; the other represents an alterity with its own rhythms of temporalization and is necessary for the enrichment of the subjective self. The relation between the subject and its other, however, is not always cooperative; there is encounter and even conflict, and it is the latter which individuates the subject. Sartre’s work in Part Three of Being and Nothingness shows that, since the gaze of the other objectifies the subject, objectification of the other (constituting the world as a subject) and objectification by the other (experiencing the other’s existence with the passivity of the body) cannot take place simultaneously, but only alternately. Thus, there cannot be a totalizing view of the world, only “a synthesis whose totality is inconceivable,” which is enriched in this incessant alternation. Beginning with this instability of differences, we need to reinterpret the self-identity of the subject and the diachronic identity of beings which are manifest. The former is based on the possibility of encountering an other, or better, the availability for the other. Arendt in The Human Conditions discussed how making and keeping promises establishes “islands of certainty in an ocean of uncertainty,” which means that our self-identity need not be based on a substantial ground and can be stabilized in the diversified field of plurality. The diachronic identity of beings, on the other hand, is protected through an intergenerational immortality that is distinguished from supratemporal eternity. The achievements which an individual can help realize are unique; this radical novelty makes the achievements survive the individual’s lifespan thanks to the witness of plural others. This fragile immortality maintains a continuity of achievements, which is needed for history and tradition, without suffocating the emergence of the new.