The object of this article is to examine, with the work of Jeremy Bentham as the principal example, one strand in the complex pattern of European social theory during the second half of the eighteenth century. This was of course the period not only of the American and French revolutions, but of the culmination of the movements of thought constituting what we know as the Enlightenment. Like all great historical episodes, the Enlightenment was both the fulfilment of long-established processes and the inauguration of new processes of which the fulfilment lay in the future. Thus the seminal ideas of seventeenth-century rationalism (in moral and social theory the idea, above all, of natural law) realized and perhaps exhausted their potentialities in the eighteenth-century Enlightenment. The ideas with which this article is concerned, however—conveniently grouped and labelled as the ideas of utilitarianism—only began to achieve systematic development in these later decades of the eighteenth century. Within that period—during the first half and more of Bentham's long life—attempts to apply those ideas to the solution of social problems met largely with failure and frustration. Yet unrealized potentialities remained, the realization of which was reserved for a time when the world of the philosophes no longer existed. The movements for social and political reform which have played so large a part in modern history since the French Revolution may be judged in widely differing ways; but whatever the verdict, these movements surely cannot be understood without due consideration of that part of their origins which lies in eighteenth-century utilitarianism.