These books are both written by eminent political historians, and both represent something of a departure for their respective authors; specifically, they represent a new interest in the rational choice theory of collective action. This turn is less pronounced in Josiah Ober's book, which employs collective action theory relatively modestly and constructively in the service of familiar aims. In Richard Tuck's book, by contrast, a direct critical engagement with collective action theory is the central theme. While each book is exceptionally learned, engaging, and informative—and thus, emphatically worth reading—neither perfectly succeeds. In my view Ober's book, which departs less from his previous interests, succeeds considerably more.

Ober describes Democracy and Knowledge as the completion of “a trilogy on the theory and practice of politics in classical Athens” (p. 30). The previous two volumes, Mass and Elite in Democratic Athens (1989) and Political Dissent in Democratic Athens (1998), established him as one of the leading scholars of classical Athenian politics. Contrasted with, say, the well-known work of Mogens Herman Hansen, these earlier works approached their subject primarily from an ideational, and not institutional, direction: Their main concern was to show how a hegemonic democratic ideology was able to sustain genuine democracy at Athens for nearly two centuries, even as it also generated a sophisticated dissenting tradition among intellectual elites. In the book under review, however, Ober moves away from ideology and turns toward institutions.

The central argument of this new book is that the specifically democratic institutions of ancient Athens enabled it to more effectively harness useful knowledge dispersed among its citizenry, and thus to significantly outperform its major rivals in a highly competitive geopolitical environment. As Ober makes clear, this is an argument about the economic and social efficiency of democracy, not a moral or ethical argument about its value; nevertheless, for those of us who believe that democracy is indeed morally superior to other forms of political organization, it is important and reassuring to learn that democracy can indeed compete on favorable terms with its rivals when necessary.

Ober's argument unfolds in three main stages. In the first stage, his aim is to establish empirically that for much of the fourth and fifth centuries b.c.e., democratic Athens not only kept pace but indeed significantly outperformed its major political and military rivals on multiple dimensions; Chapter 2 marshals considerable and compelling evidence supporting this contention. In the second stage (Chapter 3), Ober's aim is to develop a theoretical explanation for Athenian exceptionalism. Roughly speaking, the explanation advanced starts with the thought that all human communities must somehow organize the joint activities of their members in the pursuit of public aims if they are to survive competition. Joint action typically faces well-known obstacles, however: For example, there is the problem that much of the knowledge relevant for determining optimal collective aims is highly dispersed, the problem that achieving public aims often requires complex coordination, and the problem that individuals may often have incentives to free-ride on collective enterprises. Fortunately, suitably designed democratic institutions can overcome these collective action problems: Widespread participation in political processes enables citizens to share their local knowledge, align their actions and expectations with those of other citizens, and reduce incentives for free riding.

Thus far, the argument is extremely persuasive; it is only in the third stage that some problems emerge. Ober reasons that since democratic Athens did, in fact, outperform its rivals in a highly competitive environment, it must follow that its institutions successfully overcame the usual obstacles to joint action. Chapters 4 through 6 aim to document this prediction in detail. Chapter 4, for example, examines a fourth-century assembly decree authorizing the establishment of a naval station in the Adriatic Sea. The incredible complexity and detail of this decree illustrates the extent to which dispersed knowledge had been successfully harnessed and specialized activities coordinated by the Athenians. This chapter also examines the intricate structure of the Council of 500, suggesting how service on the council might build elaborate social and informational networks. And so on. Chapters 5 and 6 follow in a similar vein, the former concentrating on examples in which institutions help align diverse actions and expectations, the latter on examples in which institutions help reduce transaction costs and thus temptations to free-ride.

While all this is very interesting, nevertheless one cannot avoid the nagging feeling that there is a problem here with selection on the dependent variable: In other words, if we start by selecting an exceptional explanandum, then anything we happen to find in its proximity will seem a plausible explanans. Did not the other city-states have their own institutional mechanisms for aggregating information, aligning actions and expectations, and so on? What were these institutions like? How, specifically, did they operate differently from the Athenian institutions? Why did the Athenian institutions perform so much better? That said, it is difficult to make comparative arguments in the absence of comparative data, and so perhaps Ober should not be faulted with the limits of the source materials available to him.

The problems with Richard Tuck's Free Riding are rather different, and ultimately more serious. Much like Ober, Tuck has, through his widely influential previous writings, established himself as a leading scholar in the particular domain of his expertise—namely, early modern political thought. Unlike Ober, however, Tuck in this new book departs less from his established approach than from his established domain. This book is essentially a historically minded critique of the contemporary idea—which Tuck associates especially with Mancur Olson—that it is not rational for an individual to contribute to a collective project if his or her particular contribution seems negligible, as it does in many large collective projects, such as electing a president, contributing to public television, reducing carbon emissions, and so forth.

In order to understand what Tuck wants to argue, it is necessary to quote from Olson: “A farmer who placed the interests of other farmers above his own would not necessarily restrict his production to raise farm prices, since he would know that his sacrifice would not bring a noticeable benefit to anyone. Such a rational farmer, however unselfish, would not make such a futile and pointless sacrifice…. Selfless behavior that has no perceptible effect is sometimes not even considered praiseworthy. A man who tried to hold back a flood with a pail would probably be considered more of a crank than a saint, even by those he was trying to help. It is no doubt possible infinitesimally to lower the level of a river in a flood with a pail, just as it is possible for a single farmer infinitesimally to raise prices by limiting his production, but in both cases the effect is imperceptible, and those who sacrifice themselves in the interest of imperceptible improvements may not even receive the praise normally due selfless behavior” (The Logic of Collective Action, 1965, p. 64; quoted by Tuck, pp. 8–9). What Tuck infers from passages such as this is that Olsen derives the irrationality of contributing from the negligibility of the individual contribution. In response, he offers an extended discussion of negligibility, with the aim of demonstrating that it is perfectly rational for a person to believe that even very small contributions to a collective project are causally efficacious in a meaningful sense, and thus that they are worth undertaking.

Chapter 1 poses the general problem Tuck is interested in, and Chapter 2 distinguishes this specific problem—where individual contributions seem negligible—from various other related collective-action problems, such as the prisoner's dilemma. Chapter 3 then presents the main philosophical argument of the book: roughly that, at least provided there are a sufficient number of other contributors, it is perfectly rational for an individual to view his or her marginal contribution, however small, as having a genuine causal relationship to the relevant outcome. Provided that enough other people vote for a specific candidate, for example, I can view my additional vote as contributing to the margin of the candidate's victory. It follows that I have a reason to vote, even on a relatively narrow understanding of rationality. This seems contrary to the conclusion of Olson and his follows.

The remaining chapters are more historical. With his characteristic thoroughness and attention to detail, Tuck traces the history of the idea of negligibility, from the ancient discussions of the “sorites paradox” to the present day (Chapter 3); the connection between this and the nineteenth- and twentieth-century debates about rule and act utilitarianism (Chapter 4); and finally, the development of the current conception of perfect markets in which individual economic actors cannot influence prices unilaterally (Chapter 5). True to the author's usual form, these chapters each make for fascinating and edifying reading in their own right; it is thus especially unfortunate that they labor in support of a project ultimately resting on a mistake.

The mistake can be simply put by emphasizing the word “sacrifice” in the passage from Olson just quoted. If the issue were simply the negligibility of the individual contribution to a common project, why is this word used? Obviously, because the contribution also carries some cost for the individual contributor. The farmer who restricts his production will thereby restrict his sales; the lone crank with the pail wastes time and effort; the individual voters must go to the trouble of informing themselves, of registering in a timely manner, of conveying themselves to the polls, and so forth. Olson's point is that when individual contributions have a very small effect on outcomes, the marginal benefit to the individual of contributing (an infinitesimal increase in farm prices) is much more likely to be outweighed by the costs of doing so (reduced sales). What ultimately matters, however, is the balance, not the absolute smallness of one side of the equation. This is why (pace Tuck) the prisoner's dilemma is essentially the same—and not a different—problem. Showing that we have a reason (great or small) to contribute does not establish the rationality of contribution, unless we can also show that this reason outweighs any countervailing reasons (great or small) we have not to contribute. Judging from the failure of America to reduce its carbon footprint through the well-meaning efforts of conscientious individuals, say, it seems clear that Olson was right to worry that the balance will often favor the latter over the former.

Despite the objections canvassed here (relatively major in the case of Tuck, much less so in the case of Ober), let me reiterate that these are both books very much worth reading, if for no other reason than for the extremely rich and interesting historical detail to be found in each. In this respect, both authors live up to their justly earned reputations as great political historians. Rational choice theory is here to stay, and it is commendable that political theorists of all stripes are increasingly engaging with it in a serious manner.