Enlightenment, French siècle des Lumières (literally “century of the Enlightened”), German Aufklärung, a European intellectual movement of the 17th and 18th centuries in which ideas concerning God, reason, nature, and humanity were synthesized into a worldview that gained wide assent in the West and that instigated revolutionary developments in art, philosophy, and politics. Central to Enlightenment thought were the use and celebration of reason, the power by which humans understand the universe and improve their own condition. The goals of rational humanity were considered to be knowledge, freedom, and happiness.

The powers and uses of reason had first been explored by the philosophers of ancient Greece. The Romans adopted and preserved much of Greek culture, notably including the ideas of a rational natural order and natural law. Amid the turmoil of empire, however, a new concern arose for personal salvation, and the way was paved for the triumph of the Christian religion. Christian thinkers gradually found uses for their Greco-Roman heritage. The system of thought known as Scholasticism, culminating in the work of Thomas Aquinas, resurrected reason as a tool of understanding but subordinated it to spiritual revelation and the revealed truths of Christianity.

The successful application of reason to any question depended on its correct application—on the development of a methodology of reasoning that would serve as its own guarantee of validity. Such a methodology was most spectacularly achieved in the sciences and mathematics, where the logics of induction and deduction made possible the creation of a sweeping new cosmology. The success of Newton, in particular, in capturing in a few mathematical equations the laws that govern the motions of the planets, gave great impetusto a growing faith in the human capacity to attain knowledge. At the same time, the idea of the universe as a mechanism governed by a few simple—and discoverable—laws had a subversive effect on the concepts of a personal God and individual salvation that were central to Christianity.

Inevitably, the method of reason was applied to religion itself. The product of a search for a natural—rational—religion was Deism, which, although never an organized cult or movement, conflicted with Christianity for two centuries, especially in England and France. For the Deist, a very few religious truths sufficed, and they were truths felt to be manifest to all rational beings: the existence of one God, often conceived of as architect or mechanician, the existence of a system of rewards and punishments administered by that God, and the obligation of humans to virtue and piety. Beyond the natural religion of the Deists lay the more radical products of the application of reason to religion: skepticism, atheism, and materialism.

The Enlightenment expired as the victim of its own excesses. The more rarefied the religion of the Deists became, the less it offered those who sought solace or salvation. The celebration of abstract reason provoked contrary spirits to begin exploring the world of sensation and emotion in the cultural movement known as Romanticism. The Reign of Terror that followed the French Revolution severely tested the belief that an egalitarian society could govern itself. The high optimism that marked much of Enlightenment thought, however, survived as one of the movement’s most-enduring legacies: the belief that human history is a record of general progress.

Source of information – Encyclopædia Britannica, Inc.