The Enlightenment’s important 17th-century precursors included the Englishmen Francis Bacon and Thomas Hobbes, the Frenchman René Descartes and the key natural philosophers of the Scientific Revolution, including Galileo Galilei, Johannes Kepler and Gottfried Wilhelm Leibniz. Its roots are usually traced to 1680s England, where in the span of three years Isaac Newton published his “Principia Mathematica” (1686) and John Locke his “Essay Concerning Human Understanding” (1689)—two works that provided the scientific, mathematical and philosophical toolkit for the Enlightenment’s major advances.

Locke argued that human nature was mutable and that knowledge was gained through accumulated experience rather than by accessing some sort of outside truth. Newton’s calculus and optical theories provided the powerful Enlightenment metaphors for precisely measured change and illumination.

There was no single, unified Enlightenment. Instead, it is possible to speak of the French Enlightenment, the Scottish Enlightenment and the English, German, Swiss or American Enlightenment. Individual Enlightenment thinkers often had very different approaches. Locke differed from David Hume, Jean-Jacques Rousseau from Voltaire, Thomas Jefferson from Frederick the Great. Their differences and disagreements, though, emerged out of the common Enlightenment themes of rational questioning and belief in progress through dialogue.

Centered on the dialogues and publications of the French “philosophes” (Voltaire, Rousseau, Montesquieu, Buffon and Denis Diderot), the High Enlightenment might best be summed up by one historian’s summary of Voltaire’s “Philosophical Dictionary”: “a chaos of clear ideas.” Foremost among these was the notion that everything in the universe could be rationally demystified and cataloged. The signature publication of the period was Diderot’s “Encyclopédie” (1751-77), which brought together leading authors to produce an ambitious compilation of human knowledge.

It was an age of enlightened despots like Frederick the Great, who unified, rationalized and modernized Prussia in between brutal multi-year wars with Austria, and of enlightened would-be revolutionaries like Thomas Paine and Thomas Jefferson, whose “Declaration of Independence” (1776) framed the American Revolution in terms taken from of Locke’s essays.

It was also a time of religious (and anti-religious) innovation, as Christians sought to reposition their faith along rational lines and deists and materialists argued that the universe seemed to determine its own course without God’s intervention. Locke, along with French philosopher Pierre Bayle, began to champion the idea of the separation of Church and State. Secret societies—like the Freemasons, the Bavarian Illuminati and the Rosicrucians—flourished, offering European men (and a few women) new modes of fellowship, esoteric ritual and mutual assistance. Coffeehouses, newspapers and literary salons emerged as new venues for ideas to circulate.

The French Revolution of 1789 was the culmination of the High Enlightenment vision of throwing out the old authorities to remake society along rational lines, but it devolved into bloody terror that showed the limits of its own ideas and led, a decade later, to the rise of Napoleon. Still, its goal of egalitarianism attracted the admiration of the early feminist Mary Wollstonecraft (mother of “Frankenstein” author Mary Shelley) and inspired both the Haitian war of independence and the radical racial inclusivism of Paraguay’s first post-independence government.

Enlightened rationality gave way to the wildness of Romanticism, but 19th-century Liberalism and Classicism—not to mention 20th-century Modernism—all owe a heavy debt to the thinkers of the Enlightenment.