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.
The phrase was used by Immanuel Kant in his 1784 editorial piece responding to the question "What is Enlightenment?," where he distinguished it from private reason, by which he meant reasoning offered from a specific civic office or post. It was developed by American philosopher John Rawls to refer to the common reason of all citizens in a pluralistsociety. 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).