Those with a sense of justice aren't suckers. They wish to do right by their fellow citizens only if they are reasonably sure that their fellow citizens will do right by them. This presents an instability threat that some might find surprising: In a society filled with citizens who desire to act justly, everyone might act unjustly because they are unsure whether their fellow citizens will do the just thing. This is a basic assurance problem. John Rawls took seriously threats of instability to the well-ordered society and so was concerned about this basic assurance problem. Even after he showed that those in the well-ordered society would develop a sense of justice. Rawls still felt compelled to show that such a society would remain just. Part of doing this entailed showing how citizens in the well-ordered society assure each other that they will continue to act justly.
On one reading of Rawls's later thought, the assurance problem is solved by public reason. This solution might not be obvious, because public reason seems to have a normative purpose. The liberal principle of legitimacy, Rawls tells us, requires that we exercise political power in a manner justifiable to all. This creates a "moral, not a legal, duty"--the duty of civility--which requires that citizens "be able to explain to one another ... how the principles and policies they advocate and vote for can be supported by the political values of public reason" (Rawls  2005, 217). But in addition to this moral function, many contemporary Rawls scholars--most notably, Paul Weithman and Stephen Macedo--believe that public reason also serves a more practical role. Specifically, these scholars believe that Rawls saw public reason as solving the assurance problem alluded to earlier.
In contrast, this article argues that public reason is incapable of solving the assurance problem. If political liberals wish to take seriously the threats of instability to a liberal order that so concerned Rawls, then they must find a new solution. This article offers just such a solution to the assurance problem in the form of a costly signaling model. Our main claim is that convergence discourse, the main theoretical competitor to public reasoning, is a costly signal capable of solving the political liberal's assurance problem. That is, convergence discourse succeeds where public reason fails. Our thesis comes with an interesting corollary: The ability of convergence discourse to solve the assurance problem is a positive function of how diverse the society is. In short, the more diversity the better. This corollary is in stark contrast to Rawls' understanding of diversity as a regrettable problem to be dealt with, not something to be celebrated (Rawls 1999, 12; Rawls 2001, 3-4). However, although we claim that convergence discourse is a more effective assurance mechanism than public reason, we do not claim that this is a conclusive argument for convergence discourse over public reason.
The structure of this article is as follows: In the next section we outline the two threats of instability faced by just societies and show how they are related to one another. Moreover, we show that Rawls's solution to these two instability problems is much more nuanced than those in the secondary literature have understood. From there we outline four criticisms of public reason as an assurance mechanism. We then present our own solution to the assurance problem and show that it does not generate those criticisms raised previously against public reason; this makes our convergence discourse model preferable to Rawls's public reason model. There is a concluding section.