Paul Pierson opens his book with a fictional metaphor in which he imagines “the trendiest new restaurant in town, charmingly named ‘The Modern Social Scientist.’” He invites you to tour the restaurant as “the chef explains that the kitchen is divided into two parts.” On one side, the chef proudly points out the ingredients, called “variables.” On the other side are lovingly arrayed an “extraordinary profusion of measuring devices.” In order to prepare your favorite culinary delight, all the chef need do is combine the correct ingredients, properly measured and calibrated. In this kitchen, the length of time in which the variables are cooked, the order in which the ingredients are combined, and the relative skill of the chef are unimportant to the preparation of the meal. (Later on, the book makes it clear that the specialty of this particular establishment is something called the “multiple regression.”) Pierson concludes this metaphor with the observation that “[f]ew would want to patronize a restaurant with such a philosophy of cooking, but most social scientists are working in that kind of kitchen” (p. 1).

This is a book about the place of “time” in social science research. But time should not be just another variable in the chef's kitchen. Instead, time is the primary constituent element underpinning the sequencing of events in social reality, the temporal order within which events take place. However, the theoretically important characteristics of this temporal order are much more than the mere sequence in which events occur (e.g., the “one damn thing after another” parody of historical narratives). There are four of these characteristics, and a chapter is devoted to each of them. The first and foremost is “path dependence,” which highlights “the dynamics of self-reinforcing or positive feedback processes in a political system” (p. 10). A second and related property of the temporal order is the intermittent eruption of conjunctures, which are defined as “interaction effects between distinct causal sequences that become joined at particular points in time” (p. 12). Slowly evolving social processes compose the third characteristic of the temporal order. Such processes can only be detected and properly assigned analytical salience through close study of extended periods of social time. The fourth and last characteristic concerns the trajectory of particular institutions, their emergence, persistence, and termination in time.

Although Pierson repeatedly emphasizes that stereotyped descriptions of theoretical schools of social scientists (which he describes as “highly balkanized and tribal” [p. 7]) always involve serious overgeneralization, much of the book is framed as analytical comparisons of rational choice theory and historical institutionalism. In these comparisons, he privileges practice over theory: “I will often criticize strong tendencies associated with particular techniques or theoretical approaches, while accepting—indeed emphasizing—that there is nothing about these modes of inquiry that renders these tendencies logically necessary…. The question, after all, is not just what a particular technique or theory is capable of doing in principle, but how and to what extent it is actually used in practice—a distinction that is almost always glossed over in general discussions of method and theory” (p. 9, emphasis in the original). As a consequence, parts of the book assume the form of a discursive analysis of the political science profession as a particular community of practicing scholars. From that perspective, one of Pierson's objectives is to persuade his colleagues to pay more than lip service to the temporal order of the events and behavior they analyze. In this sense, he is absolutely correct when he says “I cannot emphasize enough that this is not a book about methods” (p. 7, emphasis in the original).

Although Pierson does not contrast rational choice and historical institutional in the way I am going to propose here, much of what he presents appears to rest upon a distinction between “preferences” and “expectations.” From a highly stylized perspective, the contrast makes sense in that much of rational choice analysis assumes preferences and rules (institutions) as given and then analyzes the interaction between them. The spare architecture of the approach, as Pierson notes, decontextualizes the event or decision to be explained by basically assuming away the temporally driven processes through which preferences form and rules (as institutions) evolve. Although historical institutionalism is a more diverse research community (and Pierson faults some of the practitioners for indulging themselves in “history as the study of the past” [p. 4]), he sees the analysis of path-dependent processes as the common focus of study. In fact, all the analytically important characteristics of the temporal order can be more or less reduced to aspects of path-dependent processes.

This, of course, is obviously the case for path dependence itself. But it is also true for conjunctures. We can conceive path-dependent processes as autonomous galaxies of dynamically reinforcing social elements that move through time. As long as they are left undisturbed, the central object of these processes (e.g., two historically dominant parties in a first-past-the-post electoral system) is continually reproduced. The microfoundations for that reproduction reside in the expectations of individuals, often in a subconscious taken-for-granted acceptance of the status quo. As constituent features of the social reality in which we live, such path-dependent processes come in uncountably large numbers and inconceivably wide varieties. (This, incidentally, is one reason Pierson's book will have an impact much wider than our own discipline.) Anyone who has ever answered the questions of a three-year-old subsequently realizes just how much of the social world has no better explanation than “that is simply the way it is.”

A conjuncture is the collision of two previously autonomous, often unremarkably reproducing, path-dependent processes (galaxies) such that the expectations supporting one or both of them are destabilized. Outside of such conjunctures, in fact, only close historical study can detect most path-dependent processes because their central characteristic is the slow-moving, incremental evolution of their relations to their central feature. Finally, the conjuncture of two or more previously autonomous processes often produces (and thus explains) the birth or death of social institutions. In their successful emergence, expectations become consciously attached to them in such a way as to reinforce their reproduction. In their decline and fall, expectations move, again consciously, in the reverse direction. In between, individual expectations are often subliminal (in part because our attention is usually focused on conjunctures that are much more dramatically exciting and in part because the sheer complexity of life demands that we accept most of social reality as given).

In sum, Pierson has provided historical institutionalism with a theoretical foundation that ultimately rests on individual expectations with respect to the future. In ways that I do not think would surprise him, such a foundation combines easily with at least some of the traditional concerns of rational choice theorists. For example, many collective action and coordination problems arise out of particular patterns of simultaneously held individual expectations and preferences. In addition, as irreducible units of social reality, almost all individual expectations and preferences are imputed rather than observed. Although Politics in Time takes us quite a way toward such a theoretical convergence, that project is still, of course, incomplete.