 Although much of the debate regarding public reason’s content has focused on the question of normative content, there are also important questions about the other aspect of public reason’s content—what Rawls describes as the guidelines of inquiry. Rawls suggests that these guidelines of inquiry direct citizens to abstain from appealing to “comprehensive religious or philosophical doctrines—to what we as individuals or members of associations see as the whole truth—nor to elaborate economic theories of general equilibrium, say, if these are in dispute”. Instead he suggests citizens must rely on “plain truths now widely accepted, or available, to citizens generally,” which include the conclusions of science when not controversial (Rawls 1996, 224–225). One interesting issue is how testimony from scientists and other experts is to be incorporated into the guidelines of inquiry (see Donahue 2020). There is at least one other puzzling aspect of this proposal. As Rawls concedes, one of the things that reasonable people disagree about is the nature of truth itself. There are competing philosophical theories of truth, and public reason is meant to abstain from appealing to particular philosophical doctrines. Rawls thus famously suggests that his account of political liberalism, of which the idea of public reason is a central part, “does without the concept of truth” (Rawls 1996, 94). But without a concept of truth, how can we make sense of what Rawls says about the guidelines of inquiry, in particular his claim that citizens should rely on “plain truths now widely accepted”? Some argue that Rawls is mistaken, and political philosophy cannot abstain from at least some controversial claims about the nature of truth (Estlund 1998; Raz 1990). Others accept that political philosophy must abstain from controversial philosophical theories of truth, but insist that public reason requires a “political” (as opposed to philosophical) account of the truth (Cohen 2008). This is discussed further in section 7.