We live in polarized times. In the United States, as in many Western European countries, citizens are increasingly divided over values and ideologies. The recent rise of right-wing populism and of extremist political parties and movements is only one of the symptoms of this polarization, which is also pervasive within mainstream parties and institutions. Although political scientists have dedicated numerous and extensive analyses to the problem of polarization and political conflict, political philosophers have been less concerned with these themes. Kevin Vallier’s book Must Politics Be War? Restoring Our Trust in the Open Society therefore provides a much-needed contribution to this debate.

The book is beautifully written and rich with both philosophical insights and references to the empirical social science literature, especially that examining social norms and trust. And social trust is indeed the central theme of the book. More specifically, Vallier argues that liberal norms and institutions can contribute to guaranteeing social trust among citizens who endorse different ethical, religious, and philosophical conceptions of the good, and can thus sustain moral peace. But this, Vallier claims, is only possible if those norms and institutions are publicly justified by appealing to “intelligible” reasons—that is, reasons grounded in the values and ideals (the “evaluative standards”) of each individual citizen. Only the appeal to such reasoning can ensure that citizens do not have to obey rules and institutions that are alien to their deepest values and commitments, and thus are able to sustain mutual trust among each other.

The book is divided into two main parts. The first part, comprising chapters 1–3, illustrates the evaluative pluralism that underlies deep disagreement in contemporary liberal democracies, explains the importance of social trust and social capital, and defends the intelligibility conception of public justification that, for Vallier, can help citizens to justify moral rules and sustain a system of social trust. The second part, including chapters 4–7, moves from the analysis of moral rules to that of legal and constitutional rules, which are required when moral rules alone are incapable of guaranteeing compliance in the absence of legal enforcement and sanctions. Vallier also develops an account of publicly justified primary rights (including political, economic, and civic rights) and constitutional rules; outlines a model of stability for liberal societies; and concludes by explaining how citizens behind a “thin veil of ignorance” (p. 200) would endorse liberal primary rights, despite their deeply diverse conceptions of the good.

Although the overall argument of the book is persuasive, it is not clear that it entirely vindicates the intelligibility conception of public justification defended by Vallier both here and in some of his previous works. According to Vallier, appealing to intelligible reasons is necessary to ensure that individual citizens are not compelled to obey rules that conflict with their deepest values and commitments. But a key problem with the intelligibility conception is that it also allows each and every citizen to challenge moral and legal rules based on his or her own intelligible reasons, thus undermining the rules’ public justification and eliciting what Vallier calls the “anarchy objection” (p. 114).

Vallier is aware of this problem and, in response, argues that, alongside those grounded in their controversial religious, ethical, and philosophical conceptions of the good, “members of the public may also include among their evaluative standards the need to get along and even be reconciled to others.… In this way, a desire to live in a high-trust order can make more proposals eligible than otherwise’ (p. 115). This is a plausible response and one that Vallier reasserts later in the book, when he argues that agents behind a thin veil of ignorance will recognize the importance of endorsing an extensive set of liberal rights despite their diverse conceptions of the good. One example is freedom of thought, which Vallier believes is publicly justified because it is one of those “fundamental rights of agency [that] protect the formation of coherent agent psychologies and the minimal capacity of persons to extend their projects and plans into the external world” (p. 202).

This is a persuasive view. But it is not clear whether and how it differs from alternative conceptions of public justification that Vallier rejects here and in previous works such as Liberal Politics and Public Faith (2014), particularly from the “accessibility” conception. According to this conception, a reason offers a suitable public justification for a state’s rules if it is grounded in evaluative standards shared among all citizens. Now, this seems to be exactly what underlies Vallier’s claim that “members of the public may also include among their evaluative standards the need to get along and even be reconciled to others” (p. 115; emphasis added). In other words, this seems to be an evaluative standard that people share, despite their different evaluative standards grounded in their diverse and conflicting conceptions of the good. If two citizens are, respectively, Catholic and Muslim, they will have different evaluative standards based on their different religious faiths, but they will also have shared evaluative standards if they agree that their state should provide them with freedom of thought and religion, allowing them to practice their faiths and live alongside each other in peace.

Vallier could, of course, respond that the diverse evaluative standards linked to each individual citizen’s own conception of the good are still necessary to guarantee the kind of social trust that is central to his account. But, again, it is not clear whether and how this response would set Vallier’s argument apart from those of Rawls or other defenders of consensus conceptions of public reason, such as the accessibility one. More specifically, as Rawls argues in his Political Liberalism (2005, pp. 386–87), full (as opposed to pro tanto) public justification is only realized when citizens endorse a liberal political order based on both shared evaluative standards and their diverse nonshared conceptions of the good. Furthermore, it is well known that for Rawls the justification of state rules based on citizens’ own conceptions of the good also contributes to the overlapping consensus that guarantees the stability of a political liberal order over time. Again, it is not clear how distant Vallier’s account is from the Rawlsian one, given that, like Rawls, Vallier (pp. 107–9) considers a mere modus vivendi unstable, and both of them seem to believe that stability requires the internalization of liberal rules based on moral reasons grounded in each citizen’s own conception of the good. Compared to Rawls’s conception of public justification, however, Vallier’s account has the significant merit of examining the connection between stability and social trust (the latter aspect does not figure prominently in Rawls’s analysis); yet it is not clear that the two accounts are significantly dissimilar.

These brief critical remarks do not detract from the quality of Vallier’s argument. In fact, I believe that, when interpreted through the lens of an accessibility conception of public justification, Vallier’s account becomes even more plausible. More generally, despite the similarities with Rawlsian consensus conceptions of public reason, the wealth of theoretical insights and empirical background information that characterize Vallier’s book render it a major new statement in the literature on public justification. I hope that the reader, like me, will look forward to the book’s sequel, in which Vallier, as stated in the epilogue (pp. 220–22), will examine more closely key liberal institutions such as freedom of association, the welfare state, the market economy, and democratic governance.