Drawing on the work of Frank Michelman and Jürgen Habermas, I outline two interconnected paradoxes of constitutional democracy. The paradox of the founding prevents a purely democratic constitution from being founded, because the procedures needed to secure its legitimacy cannot be spontaneously self-generated. It displays an infinite regression of procedures presupposing procedures. The paradox of dynamic indeterminacy heads off any attempt to resolve this problem through constitutional amendment. It shows that we cannot evaluate the legitimacy of a dynamically evolving constitution based on projections of its future development. To do so, we would need a stronger basis for making probabilistic judgments about the constitution's future path. After exploring the problems of using constitutional patriotism as such a basis, I outline an alternative built on the ideas of dynamic constitutionalism and reflexive citizenship. It shows how a dynamically evolving constitution can promote its own legitimacy from within, simultaneously resolving both paradoxes.