Although Jean-Luc Nancy subtly criticizes Arendt's notion of public space, he, nor anyone else has not laid bare the reasons for his critique. Our goal is to elaborate Nancy's reticence on Arendt's notion of public space, exploring their different historical, political and ontological outlines. Although they have in common a Heideggerian framework, their attempts for detotalization and their plea for taking up responsibility for the world, they both have their very own notion of public space and its concomitant political significance. This inquiry results in claiming that Nancy's socio-ontological notion of being-together in public leads to a necessary deepening and broadening of Arendt's notion of public space and our responsibility for others and for the world. Since for both philosophers a public space safeguards our very responsibility for the world, it is crucial to elaborate the implications of different notions of public space for our responsibility. In doing so, we offer a more profound insight into the meaning that politics and the interpretation of a public political space might have for us today.