What it was

The Enlightenment was the dominant intellectual movement in Western Europe and North America during the 18th century. Its defining commitments — most famously articulated by Immanuel Kant in his 1784 essay Beantwortung der Frage: Was ist Aufklärung? (“Answering the Question: What Is Enlightenment?”) — were the application of independent reasoning to all questions of philosophy, science, politics, and religion; the moral autonomy of the individual; the public and institutional acceptability of scientific naturalism; the principle of religious tolerance; and the conviction that human social and political arrangements were properly the subject of rational design rather than inherited tradition.

Kant’s famous summary of the movement’s self-conception was Sapere aude — “Dare to know.” The movement was simultaneously the inheritor of the Scientific Revolution of the 17th century and the philosophical foundation of the French Revolution and the broader political transformation of Europe and the Americas between 1776 and 1848.

Origins

The conventional date for the start of the Enlightenment is 1685, the year of the Revocation of the Edict of Nantes (the French royal policy that had granted limited religious tolerance to Protestants since 1598). Louis XIV’s revocation produced both the immediate emigration of approximately 200,000 Huguenots from France to England, the Netherlands, Prussia, and the American colonies, and a corresponding philosophical reaction in the receiving countries against state-sponsored religious uniformity. The Dutch Republic became, for the following half-century, the publishing centre for the most radical Enlightenment political writing, including Pierre Bayle’s Dictionnaire historique et critique (1697) and the early works of John Locke (in Dutch exile from 1683 to 1689).

The intellectual prerequisites of the Enlightenment had been built over the previous century. Galileo’s astronomy, Newton’s mathematical physics (the Principia of 1687), Locke’s empiricist epistemology (An Essay Concerning Human Understanding, 1689), and his political theory (Two Treatises of Government, 1689) had together produced a comprehensive philosophical alternative to the inherited medieval-Aristotelian intellectual synthesis. The 18th century would extend and politicize that alternative.

The major figures

The Enlightenment was a Europe-wide and transatlantic movement with distinct national traditions:

The French Enlightenment was the most centralized and the most politically consequential. Its central institution was the salon culture of Paris, in which philosophers, scientists, and political reformers met in the homes of aristocratic women (most famously Madame Geoffrin and Madame du Deffand) to discuss the issues of the day. The major French figures were Voltaire (a polymath who attacked clerical authority and religious intolerance), Montesquieu (whose De l’esprit des lois (1748) developed the constitutional theory of the separation of powers), Rousseau (whose Du contrat social (1762) developed the theory of popular sovereignty), and Diderot and d’Alembert (whose Encyclopédie (1751–1772), in 35 folio volumes, produced the largest single Enlightenment reference work).

The Scottish Enlightenment centred on Edinburgh and Glasgow and produced the most original Enlightenment work in economics, sociology, history, and philosophy. The major figures were David Hume (empiricist philosophy, religious skepticism, history), Adam Smith (moral philosophy and political economy; The Wealth of Nations (1776) is the foundational work of modern economic theory), Adam Ferguson (early sociology of civil society), and James Hutton (the founder of modern geology).

The German Enlightenment (Aufklärung) was somewhat more cautiously secular and more academically institutionalized than the French. The major figures were Immanuel Kant (whose Critique of Pure Reason (1781) is the foundational work of modern philosophy), Gotthold Ephraim Lessing (drama, theology, religious tolerance), and Moses Mendelssohn (Jewish Enlightenment philosophy; the foundation of subsequent Reform Judaism).

The American Enlightenment was the most directly political. Its major figures were Benjamin Franklin, Thomas Jefferson, John Adams, and James Madison. Their direct application of European Enlightenment political theory — particularly Locke’s Two Treatises and Montesquieu’s Spirit of the Laws — produced the American Declaration of Independence (1776) and the Constitution of the United States (1787, with the Bill of Rights added in 1791).

Core ideas

The Enlightenment’s intellectual commitments were not uniform across its figures, but several core ideas were widely shared:

  • Reason as the primary source of authority, displacing inherited tradition, religious revelation, or royal command. The slogan Sapere aude (“dare to know”) captured this commitment.
  • The natural rights of the individual, derived from human nature rather than from royal grant or established religion. Life, liberty, property, conscience, and (variously) the pursuit of happiness were the standard formulations.
  • The social-contract theory of legitimate government. Government’s legitimacy derived from the consent of the governed; arbitrary rulership was illegitimate; the state’s primary purpose was the protection of natural rights.
  • The separation of church and state. Religion was a matter of individual conscience; the state had no legitimate role in coercing religious belief or practice.
  • The constitutional separation of powers within government (legislative, executive, judicial), as articulated by Montesquieu and adopted in the American Constitution.
  • Religious tolerance, including substantial tolerance of religious dissent within Christianity and (more variably) of Judaism and Islam.
  • The application of scientific method to human affairs. The new sciences of economics, sociology, history, and psychology developed during the Enlightenment as systematic attempts to study human behaviour with the same methodological discipline as physics.
  • The conviction that human progress was possible, that material and moral conditions had improved across history and could be expected to continue improving through rational human effort.

The Encyclopédie

The single largest institutional product of the Enlightenment was the Encyclopédie ou dictionnaire raisonné des sciences, des arts et des métiers — the Encyclopédie — edited by Denis Diderot and Jean le Rond d’Alembert and published in 35 folio volumes between 1751 and 1772. It contained approximately 71,800 articles by over 140 contributors. Its explicit purpose was to compile and disseminate the intellectual results of the Scientific Revolution and the Enlightenment in a single accessible reference work.

The Encyclopédie was repeatedly subjected to political and clerical suppression. Volumes were banned by the French royal censor in 1759. Publication was suspended; the editors continued working in private. The final volumes were distributed clandestinely. The complete set was nonetheless purchased by approximately 4,000 subscribers, mostly outside France, and shaped European intellectual life for the rest of the century. Catherine the Great of Russia bought Diderot’s personal library and arranged for him to retain custody of it for life.

Political consequences

The Enlightenment’s political consequences were transformative. The American Revolution (1775–1783) and the Declaration of Independence (1776) were directly informed by Locke’s political theory and Montesquieu’s constitutional theory; Jefferson’s drafting of the Declaration is essentially a Lockean argument. The Constitutional Convention of 1787 produced the first sustained attempt to construct a polity on explicitly Enlightenment principles — separation of powers, representative democracy, individual rights, religious neutrality, and a written constitution as fundamental law.

The French Revolution (1789–1799) was a much more radical and politically violent attempt at the same project. The Declaration of the Rights of Man and of the Citizen (1789) was the French equivalent of the American Declaration of Independence; the abolition of feudal privileges (4 August 1789), the secularization of the Church, and the constitutional monarchy of 1791 were direct applications of Enlightenment political theory. The Revolution’s subsequent radicalization into the Terror of 1793–1794 produced a sustained late-Enlightenment crisis about whether the Enlightenment’s own commitments — popular sovereignty, secular politics, abstract reason — necessarily produced political violence.

After

The Enlightenment’s intellectual hegemony in Europe broke down between 1789 and 1815 — first through the Revolution’s collapse into the Terror, then through the Napoleonic Wars, then through the conservative reaction of the Congress of Vienna (1814–1815). The Romantic movement that followed in the early 19th century was, in significant part, a reaction against Enlightenment rationalism, scientific naturalism, and political universalism.

The Enlightenment’s institutional legacies, however, persisted and expanded. The American constitutional model, the French civil-rights tradition, the German university system, the British liberal political tradition, modern science, and the secular state all descended directly from the 18th-century movement. So did, more controversially, the cluster of practical commitments — universal human rights, religious tolerance, constitutional democracy, scientific naturalism, the equality of the sexes (whose Enlightenment defenders included Mary Wollstonecraft and Olympe de Gouges) — that have constituted the political-philosophical mainstream of liberal-democratic states from approximately 1800 to the present.

The Industrial Revolution, which began in Britain in the late 18th century, was substantially the technological expression of the Enlightenment’s scientific commitments. The 19th-century European political tradition that produced the Revolutions of 1830 and 1848, the abolition of slavery in the British Empire (1833) and the United States (1865), the expansion of the franchise, and the emergence of the welfare state were continuous extensions of the Enlightenment’s basic political programme.