Rainer Forst views Rawls’s Political Liberalism (PL) as “a non-comprehensive Kantian moral-political theory,” arguing that the political conception of justice is justified using practical reason alone. In contrast, Burton Dreben holds that “Kant’s talk about practical reason is useless for understanding Rawls.” This thesis argues that Dreben’s reading fits better with the project of PL. Forst mistakenly treats political conceptions of justice as if they were categorical imperatives that independently determine the reasonableness of comprehensive doctrines, resulting in his overlooking an important feature of Rawls’s political constructivism that distinguishes it from Kant’s moral constructivism—the public justification of political conceptions of justice, given reasonable pluralism. Forst does not adequately take into account the ways in which fundamental ideas implicit in the public political culture of constitutional liberal democracies justify the political conception of justice.