The Enlightenment

The Enlightenment was a movement of ideas that ran through Europe and its American colonies from the late seventeenth century to the end of the eighteenth. Its thinkers did not share a single doctrine, and they disagreed fiercely with one another, but most of them held that human reason, applied freely and in public, could understand nature, criticise inherited authority and make life better. In applying it to religion, government, law, trade and education, they wrote many of the arguments that still frame modern politics: toleration, the separation of powers, human rights, free expression and government by consent.

The movement grew out of the Scientific Revolution and the systems of early modern philosophy, and its centre of gravity lay in Paris, Edinburgh, London, Amsterdam and Berlin. It was a European conversation rather than a national one, and it reached from Naples and Milan to Saint Petersburg and Philadelphia. It ended, or at least changed character, in the revolutions it helped to inspire, and in the reactions against it that fed the Romanticism and idealism of nineteenth-century philosophy. The wider cultural history of the period is told under the Age of Enlightenment.

Two English books of the 1680s gave the century its starting point. Isaac Newton's Principia of 1687 showed that a few mathematical laws could explain the fall of an apple and the orbits of the planets alike. Readers hoped the same method might uncover the laws of society. John Locke, writing around the time of England's Glorious Revolution of 1688, supplied a theory of knowledge and a theory of government to match. His Essay Concerning Human Understanding argued that the mind begins as a blank page and that all ideas come from experience. His Two Treatises of Government held that people possess natural rights to life, liberty and property, and that a government which violates them can rightfully be resisted. His Letter Concerning Toleration argued that the state has no business forcing belief.

Earlier thinkers mattered too. René Descartes had taught Europe to doubt received opinion, and Baruch Spinoza, in the tolerant Dutch Republic, had treated the Bible as a historical document and defended freedom of thought. The Huguenot exile Pierre Bayle's Historical and Critical Dictionary (1697) exposed contradictions in sacred history and argued that an atheist could be a good citizen.

These ideas travelled through what contemporaries called the Republic of Letters, an imagined commonwealth of scholars bound together not by a state but by correspondence. Letters crossed borders and confessional lines, carrying news of experiments, manuscripts and arguments. Learned journals reviewed new books, and royal academies sponsored research and set prize essay questions. Coffee houses, reading societies and Masonic lodges gave townspeople places to discuss public affairs, while printers in the Netherlands and Switzerland supplied books that censors elsewhere had banned.

The French thinkers of the mid-century, known as the philosophes, were the movement's most visible face. France under Louis XIV and his successors was a powerful absolute monarchy in which the Catholic Church controlled education and the censors could ban a book and imprison its author. The philosophes worked in that tension, publishing anonymously, abroad or with the quiet help of sympathetic officials.

Their meeting places were the salons, regular gatherings in private houses hosted by women such as Madame Geoffrin, Madame du Deffand and Julie de Lespinasse. A hostess chose the guests and steered the conversation, giving writers access to patrons and foreign visitors. The salons were among the few places where women took part in intellectual life on something close to equal terms.

Voltaire, born François-Marie Arouet in 1694, became the most famous writer in Europe. After a quarrel with a nobleman landed him in the Bastille, he spent about two and a half years in England from 1726. He returned an admirer of English religious toleration, of Locke and of Newton, and his Philosophical Letters of 1734 held up England as a rebuke to France. The book was burned by order of the Paris parlement. With his companion Émilie du Châtelet, a gifted mathematician who later translated the Principia into French, Voltaire did much to spread Newtonian physics on the Continent.

Voltaire was not an atheist. Like many Enlightenment figures he was a deist, believing in a creator who does not intervene through miracles or revelation. His target was what he called "the infamous thing": organised religious intolerance and the power of the Church. His satire Candide (1759), written after the Lisbon earthquake of 1755 killed tens of thousands, mocked the optimistic view, associated with Gottfried Wilhelm Leibniz, that this is the best of all possible worlds. In the 1760s, from his estate at Ferney near the Swiss border, he campaigned to clear the name of Jean Calas, a Protestant merchant of Toulouse who had been tortured and executed on a false charge of murdering his son to stop him converting. Calas was formally cleared in 1765.

Charles-Louis de Secondat, baron de Montesquieu, was a magistrate from Bordeaux. His Persian Letters (1721) used two fictional Persian travellers to satirise French customs, a device that let him criticise both church and crown. His major work, The Spirit of the Laws (1748), compared the laws of societies across the world and argued that they should suit a people's climate, religion, commerce and manners rather than follow one abstract model. His most influential claim was that liberty requires the powers of government to be divided, so that the people who make laws are not the people who carry them out or judge cases under them. The idea of separated, mutually checking powers passed directly into the constitution of the United States.

The great collective work of the French Enlightenment was the Encyclopédie, or Reasoned Dictionary of the Sciences, Arts and Crafts. It began in the 1740s as a plan to translate an English encyclopaedia and became something far larger under its editors, Denis Diderot and the mathematician Jean le Rond d'Alembert. Its seventeen volumes of text appeared from 1751 to 1765, with eleven volumes of engraved plates following by 1772. Well over a hundred people wrote for it.

The Encyclopédie aimed to gather all knowledge and arrange it by the faculties of the mind, memory, reason and imagination, rather than by theology. It gave crafts such as weaving and glassmaking the same dignity as philosophy. Its more dangerous opinions were often tucked into unlikely articles and signalled by cross-references, a way of slipping criticism past the censors. In 1759 the work lost its royal licence and was condemned by the pope, and d'Alembert withdrew, but Diderot carried on, and the later volumes were printed quietly under a false imprint.

Diderot himself had been jailed for some months in 1749 for his Letter on the Blind, which hinted that belief in God depends on the evidence of the senses. He moved towards a thoroughgoing materialism, the view that everything, including thought, arises from matter in motion, an outlook his friend Baron d'Holbach set out bluntly in The System of Nature (1770). In 1773 he travelled to Saint Petersburg to meet his patron Catherine the Great, who had bought his library and let him keep it.

Jean-Jacques Rousseau, born in the city-republic of Geneva in 1712, began as a friend of Diderot and a contributor to the Encyclopédie, and ended as the Enlightenment's most searching critic from within. He became famous in 1750 when he won a prize from the academy of Dijon with an essay arguing that the progress of the arts and sciences had corrupted morals rather than improved them. His Discourse on Inequality (1755) imagined humans in a state of nature as solitary, peaceable and free, and traced how property, comparison and dependence on others produced inequality and unhappiness.

The Social Contract (1762) asked how people could live under laws and yet remain free. Rousseau's answer was that each person should give themselves wholly to the community, which is governed by the general will, the will of citizens directed at the common good rather than at private interest. In obeying laws they have made together, citizens obey only themselves. The idea inspired democrats and revolutionaries, but critics have long worried that it can justify forcing dissenters to conform. Emile, his treatise on education, argued that children should learn through experience rather than rote. Both books were condemned in Paris and Geneva in 1762, and Rousseau spent years on the move, including a stay in England arranged by David Hume that ended in a public quarrel.

Scotland, joined to England in 1707, had lost its parliament but kept its own church, law and universities, and in the eighteenth century those universities, at Glasgow, Edinburgh, Aberdeen and St Andrews, became among the best in Europe. A small, closely connected circle of professors, ministers, lawyers and doctors, gathered in clubs such as Edinburgh's Select Society, produced a body of work on human nature, morals and society that historians call the Scottish Enlightenment. Francis Hutcheson at Glasgow argued that humans have a moral sense, an inborn capacity to approve of kindness and disapprove of cruelty, much as the eye perceives colour.

David Hume, an Edinburgh man, pushed the empirical method further than anyone. In A Treatise of Human Nature (1739–40) and the shorter Enquiries, he argued that we never observe causes producing their effects; we only see one event regularly followed by another, and our expectation that the pattern will continue rests on habit, not on reason. Morality, likewise, rests on human sentiment rather than on rational proof, and no statement of what ought to be done follows logically from statements about what is. Hume doubted reports of miracles and wrote a sceptical critique of the argument that the order of nature proves a designer, the Dialogues Concerning Natural Religion, which he left to be published after his death in 1776.

Hume's friend Adam Smith, professor of moral philosophy at Glasgow, began with ethics. The Theory of Moral Sentiments (1759) explained morality through sympathy, our capacity to imagine ourselves in another's position, and through an imagined impartial spectator whose judgement we internalise. The Wealth of Nations (1776) then examined how nations grow rich. Smith showed how the division of labour multiplies productivity, criticised the mercantile system of tariffs and monopolies, and argued that people pursuing their own gain in competitive markets often promote the general good without intending it, the famous "invisible hand", a phrase he used only sparingly. He was equally sharp about merchants who conspired against the public. Thomas Reid's philosophy of common sense and Adam Ferguson's history of civil society completed a circle that helped found the social sciences.

In the German lands, divided among hundreds of states within the Holy Roman Empire, the Aufklärung was more academic and less hostile to religion than in France. Its early leader, Christian Wolff, built a vast rationalist system on Leibniz's ideas. Expelled from Halle in 1723 after pietist theologians accused him of fatalism, he was brought back in 1740 by Frederick the Great, who corresponded with Voltaire and hosted him at Potsdam. Frederick's Kingdom of Prussia became the model of enlightened absolutism, rule by a monarch who claimed to govern rationally for his subjects' good while keeping all power in his own hands. The Jewish philosopher Moses Mendelssohn in Berlin argued for religious toleration and for Jewish civic equality, and his friend the dramatist Gotthold Ephraim Lessing made a plea for tolerance among Jews, Christians and Muslims in the play Nathan the Wise (1779).

In 1783 a Berlin clergyman asked, in a footnote in the Berlinische Monatsschrift, what enlightenment actually was. Among the replies, Mendelssohn's and Immanuel Kant's became the best known. Kant, a professor at Königsberg, now Kaliningrad, answered in 1784 that enlightenment is humanity's emergence from an immaturity it has brought on itself, the inability to use one's own understanding without another's direction. Its motto, he wrote, should be the Latin "dare to know". The obstacle is less ignorance than laziness and cowardice, the comfort of letting priests, doctors and officials think for us. Kant held that the public use of reason, a scholar addressing the reading world, must always be free, even where an officer or clergyman must obey in his post. He called his own time an age of enlightenment, but not yet an enlightened age.

Kant's critical philosophy, launched with the Critique of Pure Reason (1781), tried to settle the quarrel between rationalists and Hume's scepticism by showing that the mind itself supplies the forms, such as space, time and cause, through which we experience anything at all. His moral philosophy held that right action follows a rule one could will as a law for everyone, and that people must always be treated as ends in themselves, never merely as means. In Perpetual Peace (1795) he sketched a federation of republics governed by international law. Kant both crowned the Enlightenment and transformed it, and his work became the starting point for German idealism.

The movement had many other centres. In Milan, Cesare Beccaria's On Crimes and Punishments (1764) argued that punishment should be proportionate, public and aimed at preventing crime rather than at vengeance, and that torture and the death penalty were both cruel and useless. It influenced penal reform from Tuscany to Russia. In Naples, Giambattista Vico had earlier proposed in his New Science (1725) that humans can truly understand history because they made it, a theory of cultural development that later critics of the Enlightenment admired. Monarchs from Catherine to Joseph II of the Habsburg Monarchy borrowed such ideas to modernise their states without sharing power.

The last decades of the century turned philosophical argument into political combat. Thomas Paine, an English excise officer who emigrated to America in 1774, published Common Sense in January 1776, a plain-spoken pamphlet arguing that hereditary monarchy was absurd and that the colonies should declare independence.

When revolution came to France, the Irish-born statesman Edmund Burke responded with Reflections on the Revolution in France (1790). Burke had defended the American colonists, but he saw the French attempt to rebuild society on abstract rights as reckless. Institutions that had grown over centuries, he argued, contained a practical wisdom no single generation could reconstruct from first principles, and destroying them would lead to violence and tyranny. The book is often taken as a founding text of modern conservatism, and the Terror of 1793–94 seemed to many readers to bear out its warnings.

Replies came at once. Paine's Rights of Man (1791–92) defended the Revolution and proposed a republic, public education and pensions for the old, and he was charged with seditious libel and fled to France. Mary Wollstonecraft, a London writer and teacher, answered Burke within weeks in A Vindication of the Rights of Men (1790), then went further in A Vindication of the Rights of Woman (1792). She argued that women appeared frivolous and weak not by nature but because they were educated only to please men, and that if reason is what gives humans dignity, women must be educated to use it and allowed to live as rational, independent citizens. Turning the Enlightenment's own principles against its blind spots, she criticised Rousseau's Emile for training girls for dependence.

The American Revolution drew heavily on Enlightenment political thought. The Declaration of Independence of 1776, drafted largely by Thomas Jefferson, echoed Locke in claiming that all men are created equal, with rights to life, liberty and the pursuit of happiness, and that governments derive their powers from the consent of the governed. Benjamin Franklin, printer, scientist and diplomat, was the American most celebrated in the Republic of Letters. The Constitution of 1787 built Montesquieu's separation of powers into a federal republic, and the authors of the Federalist papers argued that a large republic with many competing interests would protect liberty better than a small one.

The French Revolution went further and faster. The Declaration of the Rights of Man and of the Citizen of August 1789 proclaimed that men are born and remain free and equal in rights, that law is the expression of the general will, a phrase taken from Rousseau,. Olympe de Gouges answered the Declaration with a Declaration of the Rights of Woman in 1791 and was guillotined in 1793. The mathematician Condorcet, the last of the philosophes, wrote his Sketch of the progress of the human mind while in hiding and died in prison in 1794. Maximilien Robespierre, an admirer of Rousseau, became the leading voice of the Terror, justifying it in the name of republican virtue. Whether the Revolution fulfilled the Enlightenment or betrayed it was the question the following century inherited.

The Enlightenment's language of universal rights was written in a world built partly on the Atlantic slave trade and on European colonial empires, and its thinkers were deeply inconsistent about both. Locke invested in the Royal African Company, which traded in enslaved Africans, and is generally thought to have helped draft a constitution for Carolina that gave masters absolute power over their slaves. Hume, in a notorious footnote, suggested that Black people were naturally inferior, and Kant developed a theory of human races ranked by capacity, although he became more critical of colonial conquest in his later writings. Jefferson wrote that all men are created equal while holding hundreds of people in slavery.

Yet the Enlightenment also produced the most influential attacks on slavery and empire. Montesquieu ridiculed the arguments for slavery with savage irony. The History of the Two Indies, published under the name of the abbé Raynal with substantial passages by Diderot, denounced European colonial cruelty and imagined an uprising of the enslaved. In 1794 the French Convention abolished slavery in the colonies, a decision forced by the uprising of enslaved people in Saint-Domingue that became the Haitian Revolution. Its leader, Toussaint Louverture, took the Revolution's declarations at their word. Napoleon restored slavery in the remaining French colonies in 1802, and Haiti won its independence in 1804. Women, the poor and colonised peoples were similarly included in the universal language and excluded in practice, and a great deal of later history has consisted of groups claiming the rights the Enlightenment declared.

Opposition was present from the start, but it gathered force from the 1770s. The term Counter-Enlightenment was popularised by the historian Isaiah Berlin in an essay of 1973, and he traced it chiefly to Germany. Johann Georg Hamann, another native of Königsberg and a friend of Kant, held that the philosophes' abstract reason ignored faith, feeling and the way thought lives in particular languages. His pupil Johann Gottfried Herder argued that each people has its own culture, language and way of seeing the world, which cannot be ranked on a single scale of progress or judged by French standards. His ideas later fed cultural nationalism. Friedrich Heinrich Jacobi argued in the 1780s that consistent rationalism ends in Spinoza's pantheism and then in nihilism.

After 1789 opposition became political. Burke was joined by the Savoyard writer Joseph de Maistre, who blamed the Revolution on the arrogance of reason and defended throne, altar and the executioner as the foundations of order. The Romantic poets and philosophers, among them Johann Wolfgang von Goethe in his youth, prized imagination, nature and individual genius over calculation, though Romanticism also inherited much from Rousseau. Some historians doubt these critics formed a single movement at all.

The Enlightenment did not end on a single date. Its ideals of toleration, rights and scientific progress continued in liberalism and in the utilitarian reformers led by Jeremy Bentham, while its critics' emphasis on history, culture and community shaped conservatism, nationalism and Romanticism. Kant's critical philosophy, reworked by Fichte, Schelling and Georg Wilhelm Friedrich Hegel, launched the German idealism with which nineteenth-century philosophy began. In the twentieth century, thinkers of the Frankfurt School and later Michel Foucault asked whether Enlightenment reason had itself become a tool of domination, a debate followed in continental philosophy. The argument over what the Enlightenment achieved, and whom it left out, is still going on.