This article explores the historical and philosophical backgrounds that inform the appropriation of the term “public reason” in liberal theory. Particularly, it studies the differing nuances attached to public reason by Kant and Rawls. The article suggests that, while Kant viewed the public use of reason as a conditio sine qua non for Enlightenment to take place within the Prussian society, Rawls’s notion of public reason in Political Liberalism serves a different purpose in our contemporary world. Rawls sees public reason as a tool, which would enable citizens of the pluralistic liberal state to unearth tolerable bases for coexistence, despite their trenchant and often conflicting ideological, cultural and religious differences. Moreover, Rawls’s notion of public reason aims at liberal legitimacy: the normative and political justification of the legal power of the state in liberal democracy.