The nineteenth century is perhaps most notable for an intellectual pluralism and a conflict of ideas to a degree never before witnessed. The philosophy of the Enlightenment, which emerged during the seventeenth century and reached its apogee in the eighteenth century, advocated the vigorous unrestricted application of argument and the studious appeal to evidence. It did not, in the nineteenth century, throw up one clear set of rationally based conclusions as to the nature of reality, knowledge, values and the best social order, as one might suppose it would given the ideals of argument and evidence. It did not deliver a singular definitive worldview or Weltanschauung (a term that came to have its modern philosophical meaning during the nineteenth century). Negatively it did, nevertheless, forever cast suspicion on protected authority, divorced from truly penetrating questioning and argument. Positively, it delivered up an abundance of scientific and technical success, which in the nineteenth century accelerated and increased to a level never before seen. It was at the intellectual foundation, in philosophy, that it failed to ground the whole edifice of human understanding once and for all. This was because of a problem that persists in philosophy to this day: the intellectual tools that would be used to attempt to ground the whole of human understanding themselves necessarily come into question in such an attempt. This is clearly a case of trying to lift oneself up by one's own bootstraps. Various answers have since been developed to try to avoid, dismiss or at least ameliorate this problem; or else, finally, accept it as inevitable.