This article characterizes the Enlightenment by identifying it on a formal level with an expansive view of truth and on a content-level with a non-pessimistic conception of human nature. These two traits differentiate the Enlightenment from other forms of free thought that were already present in the seventeenth and eighteenth centuries. In particular, they differentiate it from Libertinism, in which, on the level of content, it is possible to find many of the theses later advocated by the philosophers of the Enlightenment. For instance, regarding religious issues, we already find beliefs of a deist, atheist and agnostic nature developed in the libertine thought. But in the libertine vision such truths were not to be disseminated. They were to remain the secret patrimony of the aristocratic elite, since it was socially and politically dangerous for people to learn that revealed religions are false or that God does not exist. Moreover, in the libertine thought we find a pessimistic conception of human nature. With the Enlightenment both characteristics of the freethinking prevalent in the seventeenth century disappear.
Francesco Allegri (Wed,) studied this question.