Abstract.According to Popper's critical rationalism, the possibility of disagreement is at the heart of open societies. If this is assumed to be true, is it not illiberal to try to justify principles of justice, which can be regarded as the subject of an unending collective deliberation? I suggest that it is not, using an analogy with scientific progress. Moreover, I try to show that Rawls's achievement is misunderstood if one forgets that it is supposed to overcome the antinomy between “la liberté des Modemes” and “la liberté des Anciens.” In this respect, I insist on some unnoticed similarities between Rawls's and Popper's points of views. I conclude on the idea of the “neutrality” of the theory of justice, suggesting a link between Rawls's approach and the French republi