We conveniently think of the Enlightenment as a single broad current of inspiration—a mind-set that has shaped the agenda of countless intellectual quests and specialties ever since. This is fair enough, as far as it goes, but it does not do justice to the complexities and antipathies coexisting among many schools and persuasions. Like a vast river opening into a delta of smaller channels, its branches often appeared to be taking opposite directions. The key idea that social and political life stood to be reordered—and infinitely enriched—by application of rational analysis to human affairs gave rise to sharply different interpretations. Here, Gabriel Tarde could no more escape taking sides than could any other heir of the Enlightenment.

In its earliest and most optimistic manifestations, Enlightenment thinking foretold nothing short of a broad triumph of rationality in all domains of human affairs. Figures like Saint Simon, Comte and Condorcet placed their faith in new institutions and forms of authority based on scientific wisdom. Superstition and strife would give way to cooperation based on shared, rational understandings of the best forms of governance. Conflicts spawned arising from authority based on myth and superstition would give way cooperation based on universal respect for scientific understanding of human affairs.

Politics, in Saint Simon's famous slogan, would give way to administration. Against such uplifting visions of a brave new world, many nurtured far darker expectations. A number of thinkers placed themselves outside the Enlightenment tradition altogether—de Maistre and Bonald, notably—recoiling from any notion of guidance for human affairs through reason. Others, less categorical than this, still found themselves unable to discern the workings of reason in much of France's revolutionary history. The recurring sequences of popular violence, followed by change in governing institutions, seemed to offer as many disquieting examples of carnage and inhumanity as it did steady steps toward a more rational world. The works of Hippolyte Taine portrayed revolutionary events as bloodbaths animated by something akin to collective madness, where the overthrow of civilized restraint opened the way to sadism and destruction for its own sake.