The idea that public reason provides the basis for justifying normative claims, including fundamental ethical and political claims, has acquired new resonance in recent decades. Yet it is not obvious whether or how the fact that a process of reasoning is public can contribute to fundamental justification. Indeed, since conceptions of reason, of the public and of the boundaries between public and private are various and strongly contested, any claim that public reason justifies is multiply ambiguous. Moreover, some popular conceptions of public reason are quite ill-suited to any justification of fundamental norms. I offer three contemporary examples.

First, reasoning might be thought of as public simply because it is actually done in public or by the public, for example in a context of political debate or of discussion in the media. Publicity in this sense may be crucial for any proposal to have democratic legitimation, variously conceived; but it cannot supply fundamental justifications. Democracies presuppose bounded territories and distinctions between citizens and non-citizens, and more broadly between members and non-members (aliens, resident and other); democratic process presupposes at least a rudimentary range of institutions such as the rule of law and at least minimal personal and civil rights. All of these demarcations and institutions would themselves have to be justified before democratic legitimation could be seen as providing or contributing to any fundamental form of normative justification. Similar points are true of those more widely conceived forms of public reasoning or debate which are structured by powerful formative institutions – publishers, the media, telecommunications providers, educational institutions, to name but a few – whose nature and influences would once again themselves have to be justified before the processes of public debate they structure could be seen as providing or contributing to any fundamental form of normative justification.

A second view of public reason locates its justificatory power not in democratic process, narrowly or widely conceived, but in the shared, publicly accepted categories and norms of communities. In communitarian writing we find a version of the thought that the fundamental categories and norms (of a community, of a tradition) are constitutive of identities, so cannot coherently be questioned (they are nicht hintergehbar), so by default achieve what must pass for the most fundamental sort of justification that can be mustered.