by Pamela C. Corley, Amy Steigerwalt, and Artemus Ward. Stanford, CA: Stanford University Press, 2013. 216pp. Cloth $50.00. ISBN 978-0-8047-8472-6. E-book $50.00. ISBN 978-0-8047-8632-4.

Reviewed by Christopher Zorn, Department of Political Science, Pennsylvania State University. E-mail: zorn [at]


The "puzzle" in this slim volume's title refers to the fact that – despite its outsized personalities, hot-button cases, and an agenda process that seems custom-designed to generate conflict – a substantial plurality of the U.S. Supreme Court's decisions are rendered unanimously, and a small majority are either unanimous or "highly consensual" (decided with only a single dissenting vote). Corley, Steigerwalt, and Ward's goal is to divine what leads to such consensual outcomes. To that end, they offer a general theory of consensus on the Supreme Court, and a series of supportive empirical analyses (both quantitative and qualitative).

On balance, theirs is a successful effort. The focus on consensus (rather than, say, the ideological direction of case outcomes) means that a number of conventional influences on the justices' decisions have to be tweaked somewhat, and the authors do a solid job of doing so. While one can quibble with any set of decisions about sources, data, and the like, they are generally clear and careful both in describing those choices, setting out their likely effects on the conclusions they draw, and discussing the robustness of those findings. And the consistent integration of specific examples and discussions of actual cases throughout the more quantitative parts of the book make it an engaging read.

Chapter 2 provides an overview of the theory, and a summary of their quantitative data. Broadly, their theory begins with a roundup of the contemporary "usual suspects" in judicial decision-making: legal factors, attitudinal (that is, ideological) influences, and "strategic" factors, along with institutional and case-level characteristics. Their theoretical apparatus builds upon recent work by Bert Kritzer, Brandon Bartels, and others who situate law as a constraint on the justices' ability to decide cases based on policy preferences alone. Their ongoing metaphor for the law's moderating influence on ideological preferences is the "jaws of a vise": "If the jaws are sufficiently tight, the object does not fit through or does so only such that the vise subsequently shapes it" (p.66). Whatever one thinks of that metaphor -- and to my mind, a Play-Doh Fun Factory might be a closer if less visually compelling analogue -- the empirical implications are clear: clarity in the law acts as a brake on ideological behavior, and in doing so both directly (by making decisions "easy") and indirectly (by muting ideological differences) fosters consensus.

Chapters 3 and 4 comprise the central [*181] empirical contributions of the book. Corley, Steigerwalt and Ward tackle the general question of when and why the justices' decisions in cases are consensual, operationalized in Chapter 3 in terms of votes (as either unanimous and/or "highly consensual," that is, with a single dissenting vote) and in Chapter 4 in terms of opinions. Those chapters -- which are nearly carbon-copies of each other in both their organization and their conclusions -- offer (in my view) two key findings. First, they show no important association between institutional factors (e.g., provision of law clerks, formalization of dissent assignment, etc.) and consensual outcomes, and precious little influence for strategic factors as well. Second, legal uncertainty plays a key role; it is both negatively associated with consensual outcomes and shown to moderate the association between those outcomes and ideological polarization. That is, legally "easy" cases are both more likely to be unanimous or highly consensual, and the negative association between ideological polarization and consensual outcomes is stronger in "hard" (uncertain) cases than in ones where the legal landscape is more settled.

This latter result, which is arguably the book's core empirical contribution, at once claims both too much and too little. On the one hand, the authors consistently overstate their claims about the causal nature of the processes described. The empirical findings are consistently described in terms of "influence," as in "when the level of legal certainty is low, attitudes significantly influence whether the decision will be unanimous or highly consensual" (p.110). Our discipline has recently seen a resurgence of caution in its willingness to draw causal conclusions from observational data, and while some of the claims made in the book are clearly defensible, others rest on somewhat thinner ice, especially when concerns about endogeneity can be raised. Their consistent finding that salient decisions are less likely to be decided consensually tops this list, particularly when salience is measured as front-page mentions in the New York Times; it isn't hard to imagine a world in which the Times is less likely to feature stories on cases decided unanimously, rather than the other way around.

At the same time, the authors' focus on the law's constraining power over attitudes likely undersells the true breadth of their theory. A close reading of their empirical findings suggests that it is not only ideology but in fact a range of influences that are attenuated when the Court decides "easy" cases. The aforementioned salience is one example: ignoring endogeneity concerns for the moment, the empirical results suggest that the large differences in consensual outcomes between salient and non-salient cases are substantially smaller in cases where the law is highly certain. In other words, the "vise" of the law limits not only ideological influences, but others as well.

These key theoretical and empirical chapters are sandwiched between two others that are quite different from the rest. Chapter 1 presents a qualitative / historical account of the rise of dissensus. In contrast to earlier studies in this vein that have been largely quantitative, the authors mix descriptive statistics with a careful review of the developments on the Court during the [*182] 1930s and 1940s that led to the rise of a more dissensual Court. While their findings are not especially novel, they are presented with greater nuance and attention to historical context than any other work on the topic to date. Chapter 5 considers agenda-setting, and specifically the question of the Court's decision to hear and decide cases that are subsequently decided unanimously. It draws on data from the Court's 1989 Term and again mixes descriptive quantitative analyses with a qualitative investigation of the reasons underlying the Court's certiorari grants, the latter drawing heavily on the papers of Justice Blackmun. These chapters, while quite strong on their own, are at least somewhat distinct from the book's main theoretical premise.

In the end, THE PUZZLE OF UNANIMITY is likely to raise as many questions as it answers. For my money, this is a good thing; future work will necessarily have to engage with the findings therein. While we're instructed, in writing these reviews, not to wish that the authors had written a different book, the relative novelty of the subject matter and the openness of the questions makes it reasonable to ask what else might be done in this area. For what it's worth, analyses of individual justices top my list. Certain justices have reputations for being "lone wolves" in their dissents (the first Justice Harlan is the archetype, but Burger-era Justice Rehnquist also comes to mind). Whether and when particular justices were more or less likely to dissent alone would be a natural and informative complement to the book's case-level analyses.

Copyright 2014 by the Author, Christopher Zorn