This chapter develops the idea of public reason based on the shared reasons account of public justification. It is argued that the moral foundation for political liberalism delimits a narrow scope for the idea of public reason, such that public reasons are required only for matters of constitutional essentials and basic justice. It is also argued that where public reason applies, persons as citizens have a moral duty to never appeal to their comprehensive doctrines when engaging in public reasoning. Hence, an exclusive account of public reason is vindicated. Finally, we respond to various potential objections to our view, such as the claim that the shared reasons view requires identical reasoning and the claim that public reason is interderminate or inconclusive.