Most political philosophers believe that in justifying a conception of justice, we may draw on any claims that seem both true and relevant in establishing which principles ought to regulate the distribution of rights, goods, and other things that are properly the subject of a theory of justice. In particular, claims about human flourishing or the good life, as well as metaphysical arguments and controversial philosophical theories, might play an important role in justifying the correct theory of justice.

In Political Liberalism, John Rawls challenges this assumption. He argues that we must find a way to justify a theory of justice that does not appeal to controversial ideas from religion, morality, or philosophy – ideas that will always be the subject of reasonable disagreement. Instead he proposes that we ought to construct a conception of justice that is “political.” Political conceptions have three main characteristics (PL 11–15).

First, the scope of a political conception is limited to the rules and norms regulating “the basic structure of society” – that is, society’s main political, social, and economic institutions. A political conception is still a moral conception – it contains moral ideas and values – but it is not a “comprehensive” moral theory or doctrine in that it does not include “all recognized values and virtues within one rather precisely articulated system” (PL 13), with the aim of providing guidance for most aspects of human life. In particular, a political conception does not regulate (except indirectly) the many institutions and forms of life (e.g. churches and private associations) that exist in civil society or what Rawls calls the “background culture” (PL 14).