In this article, I intend to analyse the theory of democracy developed by Chantal Mouffe. This theory aims to revitalise, from a practical point of view, modern democracies in crisis. It also aims to overcome, from a theoretical point of view, the limits of the debate between universalism and communitarianism. My thesis is that Mouffe's agonism does not capture the nature of political conflict. In spite of the criticism of essentialism that characterises both universalism and communitarianism alike, Mouffe reintroduces a discrimination between acceptable and unacceptable conflicts, paradoxically re-proposing an essentialist interpretation. I will show, in the second part of the article, how a certain form of realism, which I call 'polemic' and which is based on the reading of two classical authors of the early modernity, Niccolò Machiavelli and Baruch Spinoza, can contribute more effectively than Mouffe's agonism to determine the theoretical status of conflict in democracy.