Political integration has been part of the European project from its very beginnings. As far back as the early seventies there was concern in Brussels that an ingredient was missing in the political integration process. ‘Output legitimacy’ – the permissive consensus citizens grant to a government that is ‘delivering’, even if they do not participate in setting its goals – could not sustain unification indefinitely. Such a lacking ingredient – or ‘soul’ – has been labelled ‘European identity’ (EI) in an abundant and growing academic literature. According to Aristotle, ‘polity’ is a specific ‘constitution’ (regime or politeia) of a ‘city’ (or polis): a (‘political’) community composed of ‘citizens’ (politai). No polis can exist unless the politai come together to form it and sustain it. But what will gather and keep them united? Citizens can be very diverse regarding their language, history, religion or economic activity. In absence of a motivation, diversity of itself will make each member of a community go their own way. What kind of bond is required among very diverse European citizens to keep their polis (the EU) – their political community – together? In this paper I analyse several responses – culture, deliberation, welfare, power, multiplicity. Then I attempt a synthesis suggesting that the answers might be referring to different aspects of a single notion – rather than exhaustive explanations of it. Finally I mention three issues regarding the concept of EI that require further study.