The nineteenth century produced many thinkers who believed in the idea of inevitable social progress and perfectibility, and their ideas have been the dominant influence on most social thought since then. Social theorists imagined few, if any, limits on reformers’ aspirations and pretensions or their ability to recast human institutions to fulfill their desires. Whatever their disagreements, both conservative and radical social concepts were consummately ambitious and shared grandiose, universalistic objectives. As each school articulated its notions of the foundations of the historical and social experiences, they created ideologies that ignored many dimensions of history. Both in substance and method, the dominant assumptions and pretensions of social ideas were, to varying degrees, both comprehensive and optimistic. They always emphasized their understanding rather than their ignorance, and their unifying premise was that increasing insight, even certainty for many schools of thought, lay within human grasp.