Chief Justice William Rehnquist once wrote that the 2004 case Locke v. Davey illustrated the reality of “play in the joints” jurisprudence involving religion. This phenomenon arises when a state's actions in honoring the First Amendment's Free Exercise Clause may, in fact, violate that same amendment's Establishment Clause. In Locke, the question was whether the state of Washington was required to honor the college scholarship awarded to Joshua Davey, a student who had declared a major in “devotional theology.” Did the Free Exercise Clause require the government to give Davey the scholarship, or did the Establishment Clause justify Washington's refusal?

These “play in the joints” questions are at the heart of Kent Greenawalt's latest book, When Free Exercise and Nonestablishment Conflict. Greenawalt meticulously details the inherent tensions in the religion clauses of the First Amendment. Though he argues that these tensions are largely unavoidable in light of the language of the First Amendment, he does offer possible solutions to these important problems before eventually concluding, “At their core the clauses fit together” (247). But this book is not necessarily about offering answers. It is about asking difficult questions while highlighting the conflicts that do exist in this domain of constitutional law and politics.

Greenawalt structures his book in an effective way, dedicating each section and its respective chapter(s) to broad themes emphasizing the tensions between free exercise and nonestablishment. This structure is both helpful and necessary, given the complexity and overlapping nature of the issues he tackles. And while there are moments when the book reads like Greenawalt is simply introducing and briefly commenting on a variety of related U.S. Supreme Court cases, I am not sure this is avoidable given the sheer number of cases he must consider.

In part one, Greenawalt presents “the most straightforward tension” in the religion clauses: the government's participation in religious practices (19). Specifically, he highlights cases where the courts have weighed in on religious symbols in public places, legislative prayer, military chaplains, and more. While Greenawalt does occasionally offer solutions to these tensions—for example, he argues that religious symbols may be permitted on government property assuming certain conditions are met—concrete answers are often lacking. Given the framing and setup of the book, this is not a surprise, nor is it a letdown.

Part two shifts gears to touch on the problem of government aid to religious entities. In citing cases involving tax credits, competitive grants, and controversial “Blaine” amendments, Greenawalt suggests that these conflicts may (and, in many instances, should) end up being resolved apart from Supreme Court pronouncements and instead at state and local levels—this is, he writes, “a basic theme of the book” (80).

Greenawalt then turns to the special case of religion in public schools in part three. Over the course of these chapters, he argues several points, including: that schools should be allowed to teach religion as they would any topic, so long as it is taught from a neutral, positive perspective; that evolution ought to be taught in schools, but intelligent design could be offered as a competing account; and that while teachers cannot proselytize to students in the classroom, they should be allowed to share their experiences in certain “official” contexts.

Greenawalt next turns from constitutional disputes and legal doctrine to questions of broader concern. First, in part four he asks and answers the question of whether religious beliefs should be treated as special relative to nonreligious beliefs. “The difficulty of determining what counts as religion,” he concludes, “can itself constitute one argument for not drawing a line between religious claims and otherwise similar nonreligious claims” (200). Then, in part five he considers what kinds of arguments people should make in the public square, eventually siding with the primacy of public reasons over narrow, religious ones (226).

Greenawalt's motivation for this book does not come solely from the ivory tower. Indeed, much of what he writes about has played out before the Court in recent years—his examples from section one include recent cases involving legislative prayer (Town of Greece v. Galloway) and funding to religious bodies for nonsectarian purposes (Trinity Lutheran Church v. Comer). These cases drive home the point that Greenawalt's work here is not a purely academic exercise, but rather an attempt to deal with present conflicts in constitutional interpretation.

Perhaps the most salient part of this book is part two's chapter on religious exemptions. In a larger conversation on whether the government is required (or, alternatively, allowed) to grant exemptions from general statutes and requirements to religious objectors, Greenawalt raises the issue of same-sex marriage. Specifically, he considers whether people must participate in same-sex wedding ceremonies, even if they offer religious objections to doing so (130). The Court's looming decision in Masterpiece Cakeshop v. Colorado Civil Rights Commission makes this discussion (and Greenawalt's proposed solution) particularly relevant.

In a 7-2 decision, the Court ruled for the state of Washington in Locke v. Davey. “The State's interest in not funding the pursuit of devotional degrees is substantial and the exclusion of such funding places a relatively minor burden on [Davey],” Rehnquist wrote. “If any room exists between the two Religion Clauses, it must be here.” Locke may have attempted to lay out a path forward for “play in the joints” jurisprudence, but future challenges are inevitable. Though Greenawalt's When Free Exercise and Nonestablishment Conflict does not provide every answer, it is at least a thoughtful attempt to wrestle with these past, present, and future tensions. The charge for judges, lawyers, elected officials, and engaged citizens is to thoughtfully consider what the relationship between the two religion clauses demands for law and public policy. Reading this book would be a useful first step.