Enlightenment Philosophy: Locke, Voltaire, Rousseau, Kant, and Revolution

Dare to Know: A Revolution in Thought

In 1784, Immanuel Kant answered the question "What is Enlightenment?" in a single Latin phrase: Sapere aude — "Dare to know." Have the courage to use your own reason without guidance from another authority. This was a radical proposition in a Europe where kings ruled by divine right, where the Catholic Church held institutional power over education and publishing, and where challenging received authority could result in imprisonment or exile. Yet between roughly 1680 and 1789, a network of philosophers, pamphleteers, salon hosts, and encyclopedia editors systematically dismantled the intellectual foundations of the old order — not with armies, but with books, letters, and arguments. The French Revolution of 1789 was, in significant part, the political consequence of ideas that had been circulating in Parisian drawing rooms for sixty years.

John Locke: The Foundation of Natural Rights

John Locke's Two Treatises of Government (1689), published anonymously the year after England's Glorious Revolution, established the conceptual architecture that would underwrite both the American Declaration of Independence (1776) and the French Declaration of the Rights of Man and Citizen (1789). Three claims were central:

• Natural rights: Humans possess rights to life, liberty, and property that precede and constrain government — rights derived from reason and natural law, not royal grant or scripture.
• Consent of the governed: Legitimate government requires the consent of those governed; a government that violates natural rights forfeits its legitimacy and may be dissolved.
• Separation of powers: Legislative and executive functions should be separated to prevent tyranny — an idea Montesquieu extended in The Spirit of the Laws (1748) into the tripartite division that shaped the US Constitution.

Locke also wrote on religious toleration (A Letter Concerning Toleration, 1689) and epistemology (An Essay Concerning Human Understanding, 1690), arguing that the mind at birth is a blank slate (tabula rasa) and all knowledge derives from sensory experience — a position that undermined claims to innate ideas, including divine revelation.

Voltaire: The Polemicist

François-Marie Arouet (1694–1778), who published under the name Voltaire, was the Enlightenment's most effective communicator and most dangerous critic of the French Church and aristocracy. His Lettres philosophiques (1734), celebrating English religious tolerance and empirical philosophy after his exile to England, was publicly burned in France for its implied criticism of French institutions. His Candide (1759), a satirical novella skewering Leibnizian optimism through a series of catastrophes including the Lisbon earthquake of 1755, reached a mass readership that formal philosophical treatises could not.

Voltaire's target was not religion per se — he remained a deist, believing in a creator God but rejecting revealed religion — but institutional Christianity and the fanaticism he saw as its product. His phrase Écrasez l'infâme ("Crush the infamous thing") — referring to superstition and religious intolerance — closed thousands of his letters. His campaign to rehabilitate Jean Calas, a Protestant merchant falsely executed for murdering his son to prevent conversion to Catholicism, demonstrated that Enlightenment ideas could have immediate practical consequence: royal authorities posthumously pardoned Calas in 1765 following Voltaire's campaign.

Rousseau: The Radical Dissenter

Jean-Jacques Rousseau (1712–1778) was simultaneously an Enlightenment figure and its harshest internal critic. Where others celebrated reason and civilization as progressive forces, Rousseau argued in his Discourse on the Origins of Inequality (1755) that civilization itself was the source of human corruption — that the "natural man" was free and equal, and that private property was the original sin of social organization. His Social Contract (1762) attempted a reconstruction: legitimate political authority could only rest on the "general will" of the community, which superseded individual interests.

The Encyclopédie: Knowledge as Political Act

Denis Diderot and Jean le Rond d'Alembert's Encyclopédie, ou Dictionnaire raisonné des sciences, des arts et des métiers (1751–1772) was the Enlightenment's collective monument. Comprising 28 volumes, 71,818 articles, and 2,885 plates of technical illustration, it attempted to assemble all human knowledge organized by reason rather than theology. The enterprise attracted contributions from Voltaire, Rousseau, Montesquieu, Baron d'Holbach, and hundreds of specialists.

The Encyclopédie was suppressed twice by royal and ecclesiastical authorities — in 1752 and 1759 — and Diderot was imprisoned for his earlier materialist writings. The project continued clandestinely with the tacit acquiescence of sympathetic administrators. The first edition sold 4,000 copies at high price; subsequent quarto and octavo editions reached middle-class readers across France and Europe. The cross-referencing system was weaponized: the article on "Cannibalism" referred readers to "Eucharist"; the article on "King" referred to "Tyrant." The subversive implications were built into the structure itself.

Salon Culture and the Republic of Letters

Salons — private gatherings held in aristocratic and upper-bourgeois homes, typically hosted by women — were the primary institutional infrastructure of French Enlightenment intellectual life. Marie-Thérèse Rodet Geoffrin's salon on the Rue Saint-Honoré financed much of the Encyclopédie and hosted its contributors weekly. Julie de Lespinasse's salon connected philosophes with foreign visitors; Louise d'Épinay sheltered Rousseau and corresponded with the Baron Grimm, whose literary newsletter circulated Enlightenment ideas to European courts.

• Salons circumvented formal publication censorship by creating oral public spheres
• Hostesses (salonnières) determined who spoke, in what order, and on what topics — substantial intellectual authority exercised within social constraints
• The "Republic of Letters" — the transnational community of intellectuals communicating by letter — connected Enlightenment thinkers across national censorship regimes