The 10 Most Influential Enlightenment Thinkers, Ranked

The Enlightenment was less a single school than a mood: a conviction, spreading through Europe and its colonies from the late seventeenth century to the end of the eighteenth, that reason, evidence and open debate could improve human life. Its ideas built the vocabulary of the modern world, including natural rights, religious toleration, the separation of powers, free markets, and the autonomy of the individual.

Ranking its thinkers means deciding what “influential” means. Here it means lasting impact: how much later philosophy, politics and institutions depend on a thinker’s work, both in their own century and in ours. Brilliance matters less than reach. That is why some great minds of the period fall to the honorable mentions.

1. John Locke (1632–1704)

No one did more to set the Enlightenment’s agenda. In a remarkable two-year span around 1689–1690, Locke published three landmark works. An Essay Concerning Human Understanding argued that the mind begins as “white paper” and that all our ideas come from experience, founding the British empiricist tradition. The Two Treatises of Government grounded political authority in the consent of the governed and defended natural rights to “life, liberty, and estate.” A Letter Concerning Toleration argued that the state has no business compelling religious belief.

Each of these ideas became foundational. Locke’s political theory echoes through the American Declaration of Independence, and his empiricism set the terms for Berkeley, Hume and much of modern philosophy of mind. He takes first place because his influence runs through epistemology, politics and religion at once.

2. Immanuel Kant (1724–1804)

Kant wrote the movement’s motto. In his 1784 essay “An Answer to the Question: What Is Enlightenment?” he defined it as humanity’s emergence from its “self-incurred immaturity,” and gave it a slogan: Sapere aude! “Have courage to use your own understanding!”

His Critique of Pure Reason (1781) tried to settle the conflict between rationalists and empiricists by arguing that the mind actively structures experience. His moral philosophy, built on the idea that we must treat humanity never merely as a means but always also as an end, underlies much modern thinking about human dignity and rights. Kant credited Hume with interrupting his “dogmatic slumber.” He ranks second only because his influence, while immense, was concentrated in philosophy rather than in political institutions.

3. Jean-Jacques Rousseau (1712–1778)

Rousseau was the Enlightenment’s most brilliant internal critic. His Discourse on Inequality (1755) argued that civilization, property and social comparison had corrupted human nature. The Social Contract (1762) opens with one of the most famous sentences in political thought: “Man is born free, and everywhere he is in chains.” His concept of the general will, the idea that a legitimate state expresses the collective will of its citizens, became a rallying cry during the French Revolution.

Emile, published the same year, transformed thinking about education and childhood. Rousseau also helped launch Romanticism, which makes him both a culmination of the Enlightenment and the beginning of the reaction against it. Few thinkers have been claimed by so many opposing movements.

4. Voltaire (1694–1778)

François-Marie Arouet, known as Voltaire, was the Enlightenment’s great publicist. His Letters Concerning the English Nation (1733–1734) held up English toleration, Newtonian science and Lockean philosophy as models for France. Candide (1759) skewered philosophical optimism. After the Protestant merchant Jean Calas was executed in Toulouse in 1762, Voltaire campaigned for his posthumous exoneration and wrote his Treatise on Tolerance.

He was not a systematic philosopher, which is why he ranks below the first three, but no one did more to spread Enlightenment ideas to a mass audience. A note on accuracy: the famous line “I disapprove of what you say, but I will defend to the death your right to say it” is not Voltaire’s. It was written by his biographer Evelyn Beatrice Hall in 1906 as a summary of his attitude.

5. David Hume (1711–1776)

Hume was probably the most penetrating philosopher of the age. His Treatise of Human Nature (1739–1740) famously “fell dead-born from the press,” as he later put it, but its ideas, reworked in An Enquiry Concerning Human Understanding (1748), changed philosophy permanently. He argued that we have no rational justification for expecting the future to resemble the past, the problem of induction, and that our idea of causation rests on habit rather than insight.

In ethics he insisted that “reason is, and ought only to be the slave of the passions.” His Dialogues Concerning Natural Religion, published after his death, remain one of the sharpest critiques of the argument from design. Hume ranks fifth only because his deepest influence arrived later, through Kant and twentieth-century philosophy, rather than in his own century.

6. Montesquieu (1689–1755)

Charles-Louis de Secondat, Baron de Montesquieu, gave the modern world its theory of the separation of powers. The Spirit of the Laws (1748) argued that liberty is best protected when legislative, executive and judicial power are held by different bodies that check one another. It also pioneered a comparative, almost sociological study of how climate, commerce and custom shape laws.

His influence on constitutional design is hard to overstate. In Federalist No. 47, James Madison called him “the oracle who is always consulted and cited on this subject.” His earlier Persian Letters (1721) used imagined foreign visitors to satirize French society.

7. Adam Smith (1723–1790)

Smith is remembered as the founder of economics, but he saw himself as a moral philosopher. The Theory of Moral Sentiments (1759) built an ethics on sympathy and the imagined judgment of an “impartial spectator.” The Wealth of Nations (1776) analyzed the division of labor, the workings of markets and the self-defeating nature of mercantilist trade policy.

The “invisible hand” for which he is famous appears only once in The Wealth of Nations, and Smith was far more alert to the dangers of monopoly and the power of merchants than his popular image suggests. Few books have shaped public policy so directly.

8. Baruch Spinoza (1632–1677)

Spinoza died before the high Enlightenment began, but historians such as Jonathan Israel have argued he was the source of its most radical currents. Expelled from Amsterdam’s Jewish community in 1656, he published the Theological-Political Treatise (1670) anonymously. It read the Bible as a historical document and defended freedom of thought as essential to a peaceful state. His Ethics, published after his death, identified God with nature.

For a century, “Spinozist” was a dangerous accusation. That alone shows how deeply his ideas unsettled Europe.

9. Denis Diderot (1713–1784)

Diderot was the driving force behind the Encyclopédie (1751–1772), co-edited for its first years with the mathematician Jean le Rond d’Alembert. Its seventeen volumes of text and eleven of plates aimed to gather all human knowledge, from metaphysics to manufacturing, and to change “the common way of thinking.” Despite censorship and the departure of collaborators, Diderot saw it through. As an organizer of knowledge, he made the Enlightenment a collective project.

10. Mary Wollstonecraft (1759–1797)

Wollstonecraft took the Enlightenment’s own principles more seriously than most of its leading men. In A Vindication of the Rights of Woman (1792) she argued that if reason is the basis of human dignity, women must be educated to use it, and she directly challenged Rousseau’s views on female education in Emile. Long neglected, her argument became a founding text of modern feminism.

Honorable mentions

Cesare Beccaria, whose On Crimes and Punishments (1764) argued against torture and the death penalty; Thomas Paine; the Marquis de Condorcet; Pierre Bayle; and Isaac Newton, whose physics was the model of what reason could achieve, though he was a scientist rather than a social thinker.

Conclusion

The Enlightenment’s legacy is contested, and its critics, from Romantics to postcolonial historians, have pointed to its blind spots. But its leading thinkers still frame our arguments about rights, toleration, science and self-government. Locke tops this list because so much of the modern liberal order can be traced to three books he published in a single burst. To read the period at its best, start with Kant’s short essay on Enlightenment, then Locke’s Second Treatise, then Hume’s Enquiry. Together they show reason being turned on everything, including itself.