Public reason refers to a common mode of deliberation that individuals may use for issues of public concern. The concept implicitly excludes certain assumptions or motivations that are considered improper as a basis for public decision making, even as a person may apply them in personal decisions that do not have a significant impact on the public. This is understood within the view that the members of the public are rationalized counterparts of real moral agents, considering possible moral rules and reason when making decisions.
The phrase "public use of one's reason" (Vernunft in allen Stükken öffentlichen Gebrauch) was used by Immanuel Kant in his 1784 editorial piece responding to the question "What is Enlightenment?," where he distinguished it from private usage of reason, by which he meant reasoning offered from a specific civic office or post. This Kantian conception was further developed by American philosopher John Rawls to refer to the common reason of all citizens in a pluralist society and identified it as a component of political liberalism. Although Rawls cited the Kantian origin of his concept, his understanding is distinguished by the way he explained how public reason embodies the shared fund of beliefs and reason of those who constitute a democratic polity - those who are concerned with the good of the public and matters of basic justice.
Public reason giving, in the Rawlsian sense, involves justifying a particular position by way of reasons that people of different moral or political backgrounds could accept. Although in his later writings he added what is known as the proviso, meaning that non-public reasons could be given assuming that public reasons would be provided in due course. In order to accomplish this, however, one must overcome what he refers to as the burdens of judgment, which can produce disagreement among reasonable citizens. These burdens include conflicting evidence, giving differing weights to considerations, conceptual indeterminacy, differing experiences and value conflicts. Private reason, by contrast, is the exercise of an individual's reason to the constrained norms and interests of some sub-set of the public as a whole (such as a business, a political party, the military or the family).
Rawls also classified the concept into public reason for "liberal peoples" and public reason for "society of peoples". The former involves public reason of free and equal liberal peoples who debate their mutual relations while the latter involves equal citizens of domestic society debating political issues and justice concerning their government.
- Gaus, Gerald (2010). The Order of Public Reason: A Theory of Freedom and Morality in a Diverse and Bounded World. Cambridge: Cambridge University Press. p. 267. ISBN 9780521868563.
- Kant, Immanuel. "Kant's "What Is Enlightenment"". An Answer to the Question: What is Enlightenment?. Archived from the original on 25 November 2011. Retrieved 9 December 2011.
- Deligiorgi, Katerina (2005). Kant and the Culture of Enlightenment. New York: State University of New York Press. p. 8. ISBN 0791464695.
- Rawls, John (1997). "The Idea of Public Reason Revisited". The University of Chicago Law Review. 64: 765–807. doi:10.2307/1600311.
- Rawls, John (2002). The Law of Peoples: With "The Idea of Public Reason Revisited". Cambridge, Massachusetts: Harvard University Press. p. 55. ISBN 067400079X.