This article examines the formation of British Secularist ethics in the middle decades of the nineteenth century. The Secularist movement, initiated by George Jacob Holyoake in 1851, was a primarily artisan working-class social movement that sought to ground social ethics upon a rational, scientific, and nontheological foundation. This article examines how the quest for a science of morals informed Secularist expectations and judgements. In this article, I trace how the idea of a rational science of ethics was integrated into the secularist movement. I begin by briefly situating the Secularist movement within the wider moral and epistemological debates of the mid-Victorian period. I address the implications that atheism had on the development of Secularism, and on its contemporary reputation and respectability. I then examine how Holyoake sought to establish the non-theological grounds of morality and the tensions that arose from debates between Secularists regarding the necessity of atheism to Secularism. Finally, I argue that despite significant fissures within the movement created by the question of the necessity of atheism, Secularism nevertheless evinced a high degree of conceptual unity concerning the nature and grounds of morality. Corbeil: Grounding Non-Theological Morality Art. 4, page 2 of 11 nevertheless evinced a high degree of conceptual unity concerning the nature and grounds of morality. Religion, Science, and Duty Victorian moral thinking was marked by flux, experimentation, and controversy. The fecundity of nineteenthcentury experimentation in moral philosophy occurred amid prominent fears that the transition to a modern, industrial and urban society had resulted in the loss of the vital foundations of ethics. These moral anxieties were intimately related to the problem of progress and coincided with a widely-shared belief among theorists, ranging from the utilitarian and liberal John Stuart Mill to Tory intuitionists like William Whewell, that scientific systems of knowledge would lead to ascertaining the true grounds of morality, unleashing dramatic human progress (Snyder 2006). The blending of scientism and ethics was thus not only the terrain of secular or non-theological moralists. Grounding ethics in science was urgent for all those individuals convinced, either optimistically or pessimistically, that Christianity faced terminal decline in Britain. To situate Secularist moral ideas accurately, we must address some of the more important issues that faced leading nineteenth-century moralists, and expose the connections between faith, knowledge, and obligation that formed the dominant contours of Victorian ethical discussions. Stefan Collini (1991) has productively characterized Victorian ethical thought between 1850 and the 1890s as a culture of altruism. Altruism, a term coined by Auguste Comte and introduced into English by G. H. Lewes in 1852, was constructed as a scientific triumph over Christian moral pessimism (Hilton 1992). Against what he saw as the Christian emphasis on humanity's in...