John Stuart Mill, looking back from 1843 to the appearance of Vico's Scienza Nuova (1725), observed that thinkers preoccupied with the laws of social change have “universally adopted the idea of a trajectory or progress, in lieu of an orbit or cycle.” Mill was careful to stress that in his own usage “progress” meant not necessarily social improvement but only “a course not returning into itself.” Yet his astronomical metaphor is soaring, expansive, as well as austerely scientific in its associations; and he professed his personal conviction that “the general tendency is, and will continue to be… one of improvement; a tendency towards a better and happier state.” Whether our own or any readily foreseeable state vindicates Mill's liberal optimism is often questioned (particularly by those for whom social change has meant a diminution of wealth, status, and power), but it is at least certain that the idea of progress has itself exercised an enormous influence over men's lives. For two centuries it has served both as the most widely accepted model of historical development and as the justifying secular faith of the North Atlantic peoples.