The Enlightenment developed those features of the modern world that most libertarians prize—liberal politics and free markets, scientific progress, and technological innovation.

The Enlightenment took the intellectual revolutions of the early modern 17th century and transformed European and American society in the 18th century. At the beginning of the 17th century, Europe was largely feudal and prescientific. By the end of the 18th century, however, liberal democratic revolutions had swept away feudalism; the foundations of physics, chemistry, and biology had been laid; and the Industrial Revolution was at full steam.

The Enlightenment was the product of thousands of brilliant and hardworking individuals, yet two Englishmen are most often identified as inaugurating it: John Locke (1632–1704), for his work on reason, empiricism, and liberal politics; and Isaac Newton (1643–1727), for his work on physics and mathematics. The transition to the post‐​Enlightenment era is often dated from the successful resolution of the American Revolution in the 1780s—or, alternatively, from the collapse of the French Revolution and the rise to power of Napoleon Bonaparte in the 1790s. Between Locke and Newton at the end of the 17th century and the American and French Revolutions at the end of the 18th century, there occurred 100 years of unprecedented intellectual activity, social ferment, and political and economic transformation.

Fundamental to the achievements of Locke and Newton was confident application of reason to the physical world, religion, human nature, and society. By the 1600s, modern thinkers began to insist that perception and reason are the sole means by which men could know the world—in contrast to the premodern, medieval reliance on tradition, faith, and revelation. These thinkers started their investigations systematically from an analysis of nature, rather than the supernatural, the characteristic starting point of premodern thought. Enlightenment intellectuals stressed man’s autonomy and his capacity for forming his own character—in contrast to the premodern emphasis on dependence and original sin. Most important, modern thinkers began to emphasize the individual, arguing that the individual’s mind is sovereign and that the individual is an end in himself—in contrast to the premodernist, feudal subordination of the individual to higher political, social, or religious authorities. The achievements of Locke and Newton represent the maturation of this new intellectual world.

Political and economic liberalism depend on confidence that individuals can run their own lives. Political power and economic freedom are thought to reside in individuals only to the extent that they are thought to be capable of using them wisely. This confidence in individuals rests on a confidence in human reason—the means by which individuals can come to know their world, plan their lives, and socially interact.

If reason is a faculty of the individual, then individualism becomes crucial to our understanding of ethics. Locke’s A Letter Concerning Toleration (1689) and Two Treatises of Government (1690) are landmark texts in the modern history of individualism. Both link the human capacity for reason to ethical individualism and its social consequences: the prohibition of force against another’s independent judgment or action, individual rights, political equality, limiting the power of government, and religious toleration.

Science and technology more obviously depend on confidence in the power of reason. The scientific method is a refined application of reason to understanding nature. Trusting science cognitively is an act of confidence in reason, as is trusting one’s life to its technological products. If one emphasizes that reason is the faculty of understanding nature, then the epistemology that emerges from it, when systematically applied, yields science. Enlightenment thinkers laid the foundations of all the major branches of science. In mathematics, Newton and Gottfried Leibniz independently developed the calculus, Newton developing his version in 1666 and Leibniz publishing his in 1675.The monumental publication of modern physics, Newton’s Principia Mathematica, appeared in 1687. A century of investigation led to the production of Carolus Linnaeus’s Systema Naturae in 1735 and Species Plantarium in 1753, jointly presenting a comprehensive biological taxonomy. The publication of Antoine Lavoisier’s Traité Élémentaire de Chimie (Treatise on Chemical Elements) in 1789, proved to be the foundational text in the science of chemistry. The rise of rational science also brought broader social improvements, such as the lessening of superstition and, by the 1780s, the end of persecutions of witchcraft.

Individualism and science are consequences of an epistemology predicated on reason. Both applied systematically have enormous consequences. Individualism when applied to politics yielded a species of liberal democracy, whereby the principle of individual freedom was wedded to the principle of decentralizing political power. As the importance of individualism rose in the modern world, feudalism declined. Revolutions in England in the 1640s and in 1688 began this trend, and the modern political principles there enunciated spread to America and France in the 18th century, leading to liberal revolutions in 1776 and 1789. Political reformers instituted bills of rights, constitutional checks on abuses of government power, and the elimination of torture in judicial proceedings.

As the feudal regimes weakened and were overthrown, liberal individualist ideas were extended to all human beings. Racism and sexism are obvious affronts to individualism and went on the defensive as the 18th century progressed. During the Enlightenment, antislavery societies were formed in America in 1784, in England in 1787, and a year later in France; in 1791 and 1792, Olympe de Gouges’s Declaration of the Rights of Women and Mary Wollstonecraft’s A Vindication of the Rights of Women, landmarks in the movement for women’s liberty and equality, were published.

Free markets and capitalism are a reflection of individualism in the marketplace. Capitalist economics is based on the principle that individuals should be left free to make their own decisions about production, consumption, and trade. As individualism rose in the 18th century, feudal and mercantilist institutions declined. With freer markets came a theoretical grasp of the productive impact of the division of labor and specialization and of the retarding impact of protectionism and other restrictive regulations. Capturing and extending those insights, Adam Smith’s Wealth of Nations, published in 1776, is the landmark text in modern economics. With the establishment of freer markets came the elimination of guilds and many governmental monopolies, and the development of modern corporations, banking, and financial markets.

Science, when applied systematically to material production, yields engineering and technology. By the mid‐​18th century, the free exchange of ideas and wealth resulted in scientists and engineers uncovering knowledge and creating technologies on an unprecedented scale. The Industrial Revolution, underway for some decades, was substantially advanced by James Watt’s steam engine after 1769. Items that were once luxuries—such as pottery, cotton fabric, paper for books and newspapers, and glass for windows in houses—soon became mass‐​produced.

When science is applied to the human body, the result is advances in medicine. New studies of human anatomy and physiology swept away supernaturalistic and other premodern accounts of human disease. By the second half of the 18th century, medicine was placed on a scientific footing. Edward Jenner’s discovery of a smallpox vaccine in 1796, for example, provided protection against a major killer and established the science of immunization. Over the course of the century, physicians made advances in their understanding of nutrition, hygiene, and diagnostic techniques. These discoveries, combined with newly developed medical technologies, contributed to modern medicine. At the same time, advances in public hygiene led to a substantial decline in mortality rates, and average longevity increased.

The Enlightenment also was responsible for the establishment of the idea of progress. Ignorance, poverty, war, and slavery, it was discovered, were not inevitable. Indeed, Enlightenment thinkers came to be profoundly convinced that every human problem could be solved and that the human condition could be raised to new and as‐​yet unimagined heights. “The time will come,” wrote the Marquis de Condorcet, a mathematician and social reformer who also translated Smith’s Wealth of Nations into French, “when the sun will shine only on free men who have no master but their own reasons.” Through science the world was open to being understood, to disease being eliminated, and to the unlimited improvement of agriculture and technologies. Every individual possessed the power of reason, and, hence, education could become universal and illiteracy and superstition eliminated. Because men possess reason, we are able to structure our social arrangements and design political and economic institutions that will protect our rights, settle our disputes peaceably, and enable us to form fruitful trading partnership with others. We can, they thought, become knowledgeable, free, healthy, peaceful, and wealthy without limit. In other words, the Enlightenment bequeathed to us the optimistic belief that progress and the pursuit of happiness are the natural birthrights of humankind.

Yet not all commentators regarded the Enlightenment as unrelievably progressive. Conservatives leveled three broad criticisms—that the Enlightenment’s rationalism undermined religious faith, that the Enlightenment’s individualism undermined communal ties, and that by overemphasizing the powers of reason and individual freedom the Enlightenment led to revolutions that instituted changes of such rapidity that they undermined social stability. Socialists also offered three criticisms—that the Enlightenment’s idolatry of science and technology led to an artificial world of dehumanizing machines and gadgets; that the Enlightenment’s competitive individualism and capitalism destroyed community and led to severe inequalities; and that the combination of science, technology, and capitalism inevitably led to technocratic oppression by the haves against the have‐​nots.

Contemporary debates over the significance of the Enlightenment thus have a threefold character—between those who see it as a threat to an essentially religious‐​traditionalist vision, those who see it as a threat to an essentially Left‐​egalitarian vision, and those who see it as the foundation of the magnificent achievements of the modern scientific and liberal‐​democratic world.

Further Readings

Cassirer, Ernst. The Philosophy of the Enlightenment. Princeton, NJ: Princeton University Press, 1968.

Gay, Peter. The Enlightenment. New York: Knopf, 1966. Horkheimer, Max, and Theodor W. Adorno. Dialectic of Enlightenment. New York: Continuum, 1994 [1944].

Kramnick, Isaac, ed. The Portable Enlightenment Reader. New York: Penguin, 1995.

Kurtz, Paul, and Timothy J. Madigan, eds. Challenges to the Enlightenment. Amherst, NY: Prometheus Books, 1994.

Rusher, William A., ed. The Ambiguous Legacy of the Enlightenment. Lanham, MD: University Press of America, 1995.

William, David, ed. The Enlightenment. Cambridge: Cambridge University Press, 1999.

Originally published