The Enlightenment

A new picture of the universe

In the 1500s and 1600s, a revolution in science overturned the ancient picture of the cosmos. Copernicus (1543) proposed that the earth goes around the sun. Kepler showed the planets move in ellipses. Galileo Galilei, using the new telescope, saw mountains on the moon and moons around Jupiter. Finally, in 1687, Isaac Isaac Newton's Principia showed that the same simple laws of motion and gravity govern apples falling on earth and planets circling the sun. The universe seemed like a vast, perfectly ordered machine, a great clock.

Most of these scientists were devout Christians. Newton wrote more on theology and biblical prophecy than on physics, though he privately rejected the Trinity. They believed they were "thinking God's thoughts after him." Yet the new science raised hard questions. If the universe runs by fixed laws, is there room for miracles? Does God do anything except set the clock going?

The Galileo affair

In 1633 the Roman Inquisition condemned Galileo for teaching that the earth moves, and it placed him under house arrest for life. Galileo had argued that Scripture teaches "how to go to heaven, not how the heavens go." The case became the most famous symbol of conflict between science and religion. Historians stress that it was complicated. Galileo's evidence was not yet conclusive, he had insulted the pope in print, and Catholic Jesuit astronomers were among Europe's best scientists. But it was a costly mistake. In 1992 Pope John Paul II acknowledged that Galileo's judges had erred.

Reason as the judge

The French philosopher René Descartes (1596–1650), himself a Catholic, decided to doubt everything that could be doubted. He found one certainty: "I think, therefore I am." From there he tried to rebuild knowledge, including proof of God, on the basis of reason alone. His method made the individual thinking mind the starting point, a major shift from relying on tradition and authority.

The English philosopher John Locke (1632–1704) argued that knowledge comes from experience, and he wrote The Reasonableness of Christianity (1695), presenting a simple faith based on Jesus as Messiah and moral teacher. His Letter Concerning Toleration (1689) argued that the state's job is to protect life, liberty and property, not to save souls. Force cannot produce genuine belief. (He did not extend toleration to Catholics, whom he considered loyal to a foreign power, or to atheists, who he thought could not be trusted to keep oaths.) His ideas deeply influenced the American founders.

Deism: a God who stays out of the way

A movement called Deism spread among educated people in England, France and America. Deists believed:

• A wise creator God made the universe and its laws, as the order of nature proves.
• God does not intervene through miracles, special revelation or answered prayer.
• True religion is a simple, universal, rational morality, available to all people everywhere, the same as "natural religion."
• The Bible's miracles, the Trinity, the divinity of Christ and the authority of priests are later corruptions.

John Toland's Christianity Not Mysterious (1696) argued that nothing in true Christianity is above reason. Thomas Jefferson later literally cut the miracles out of his Bible with a razor, leaving Jesus as a moral teacher. Many American founders, including Benjamin Franklin and Jefferson, were Deists or near-Deists, though others were orthodox Christians.

Faith and reason in the Enlightenment: a spectrum

Position	God	Bible & miracles	Examples
Atheism / materialism	No God	Myths	d'Holbach, La Mettrie (rare)
Skepticism	Unknowable	Miracles never credible	Hume
Deism	Creator who does not intervene	Rejects miracles, revelation, Trinity; keeps morality	Toland, Voltaire, Jefferson, Paine
Moral religion	Necessary for moral life	Religion within the limits of reason	Kant, Lessing
Reasonable Christianity	Christian God	Revelation accepted but kept reasonable; distrusts "enthusiasm"	Locke, Butler, Paley, Latitudinarians
Religion of the heart	Christian God, known by experience	Fully accepted; personal conversion central	Pascal, Pietists, Wesley, Edwards

The philosophes

In France, where the Catholic Church was powerful, wealthy and allied to an absolute monarchy, Enlightenment critics, the philosophes, were often fiercely anticlerical. The witty and tireless Voltaire (1694–1778) campaigned against religious intolerance with the slogan "Écrasez l'infâme," "Crush the infamous thing," meaning superstitious, persecuting religion. He championed the case of Jean Calas, a Protestant falsely executed for supposedly murdering his son to prevent his conversion to Catholicism. Voltaire was a Deist, not an atheist. He built a chapel on his estate "dedicated to God." The great Encyclopédie (1751–1772), edited by Diderot, spread Enlightenment ideas and slipped in criticism of religion. Jean-Jacques Rousseau proposed a "civil religion" and a natural, emotional faith outside the churches.

Under pressure from Catholic monarchs influenced by Enlightenment ideas, Pope Clement XIV suppressed the Jesuits in 1773. It was a sign of the church's weakness. The order was restored in 1814.

Skeptics: Hume and Kant

The Scottish philosopher David Hume (1711–1776) went further. In his essay "Of Miracles" (1748) he argued that it is always more likely that a witness is mistaken or lying than that the laws of nature have been broken, so no testimony can ever establish a miracle. His Dialogues Concerning Natural Religion (published after his death in 1779) attacked the argument from design. Hume's skepticism remains a classic challenge to faith.

The German philosopher Immanuel Kant (1724–1804), raised in a Pietist home, defined Enlightenment as humanity's emergence from self-imposed immaturity. His motto was "Dare to know!" His Critique of Pure Reason (1781) argued that human reason can know only the world of experience. It cannot prove (or disprove) God, freedom or immortality. But he said he had to deny knowledge in order to make room for faith. God, he argued, is a necessary assumption of moral life. For Kant, religion was essentially morality, a view that shaped 19th-century liberal theology.

In Germany, the dramatist Gotthold Ephraim Lessing published fragments by the scholar Reimarus questioning the Gospels' historical reliability, starting the "quest for the historical Jesus." He spoke of an "ugly, broad ditch" between historical facts and eternal truths.

Christian responses

Christians did not simply retreat. Their responses varied:

• Rational defense: Bishop Joseph Butler's Analogy of Religion (1736) argued that the difficulties in revealed religion are no greater than those in nature, so Deists have no grounds to reject one but accept the other. William William Paley's Natural Theology (1802) famously argued that just as finding a watch implies a watchmaker, the intricate design of living things implies a Designer.
• Reasonable Christianity: Many clergy, especially in the Church of England (the "Latitudinarians"), stressed morality, moderation and the reasonableness of faith, and avoided "enthusiasm" (religious emotion).
• The religion of the heart: Pietists, Methodists and revivalists answered cold rationalism with warm personal experience of God (see Wesley and the Great Awakening). Pascal had already said that the heart has its reasons.
• Enlightened Christianity: In Scotland, America and Germany, many Christians embraced Enlightenment values such as education, science, tolerance and human rights, and saw them as fruits of Christianity.

The road to religious freedom

Enlightenment arguments combined with the convictions of dissenters like Baptists and Quakers to advance religious liberty. Monarchs like Frederick the Great of Prussia, a skeptic, announced that in his realm everyone could seek salvation in their own way. Joseph II of Austria issued an Edict of Toleration in 1781. In America, Jefferson's Virginia Statute for Religious Freedom (1786), backed by Baptists and James Madison, ended the established church in Virginia. Its principles were written into the First Amendment of the US Constitution (1791). The next era would see the Enlightenment's most dramatic and violent consequence: the French Revolution.