Religion and the Enlightenment: Faith, Reason, and the Modern World

Few topics in intellectual history are more frequently misunderstood than the relationship between the Enlightenment and religion. The cliché of the Enlightenment as a uniformly anti-religious movement does not survive contact with the actual writings of the period. Most of the leading figures of the Enlightenment were not atheists; many were devout in their own ways; and even the most skeptical of them engaged seriously with the substance of religious belief. What they did challenge, with varying degrees of force, was the political and intellectual authority of organized churches, the credibility of miracle stories and prophetic claims, and the use of religious arguments to settle questions that could be answered by reason and observation.

The result was a complex, multi-layered conversation about faith, reason, and the proper place of religion in public life. The conversation has not ended. The contemporary debates about secularism, religious freedom, and the role of faith in public life are, in their structure, recognizably descendants of the debates begun in the seventeenth and eighteenth centuries. If you want to understand the present, you have to read this argument; most of the categories through which we now argue about religion and public life were shaped in this period.

The Religious Background

The Enlightenment inherited a deeply divided Christendom. The Protestant Reformation of the sixteenth century had shattered the religious unity of Western Europe, and the subsequent wars of religion — culminating in the Thirty Years’ War of 1618 to 1648, which killed perhaps a third of the population of central Europe and produced a famine so severe that parents are recorded as having eaten their children — had demonstrated the catastrophic consequences of using political power to enforce religious uniformity.

By the seventeenth century, European intellectual life was shaped by several religious traditions, each with its own internal disputes:

Catholicism in its Counter-Reformation form, doctrinally unified and politically powerful in southern Europe and the Catholic parts of the Holy Roman Empire, with strong missionary movements in Asia and the Americas. The Index of Forbidden Books, established in 1559, was, by 1750, a substantial catalogue; the most important Enlightenment authors were eventually on it.

Lutheranism dominant in much of Germany and Scandinavia, with a strong tradition of biblical scholarship and theological controversy. The German university theology faculties were, by the eighteenth century, the most sophisticated in Europe, and they had begun to read the Bible in historical and critical ways that the Catholic Counter-Reformation would not have permitted.

Calvinism influential in the Netherlands, Scotland, parts of Germany, Switzerland, and the Puritan communities in England and New England, with a strong tradition of moral discipline and ecclesiastical independence. The Scottish Presbyterian Kirk, in particular, was a key institution of the Scottish Enlightenment, and most of the major Scottish philosophers were at least nominally within it.

Anglicanism the established church of England, encompassing a wide range of theological positions from high church sacramentalism to evangelical piety. The Anglican settlement of 1689 was, in effect, a Latitudinarian settlement, and the Latitudinarian tradition is one of the most important and least studied elements of the British Enlightenment.

Dissenting and radical Protestant traditions including the Anabaptists, the Quakers, the Baptists, the Moravians, and various millenarian and spiritualist groups, often persecuted by the established churches. These traditions were, in the eighteenth century, the principal carriers of religious dissent, and their relationship to the Enlightenment is more complicated than the standard story suggests: the Dissenters were often, in fact, the most politically active carriers of Enlightenment ideas.

Judaism a long-established but increasingly marginalized religious community, subject to legal disabilities in most European countries. Moses Mendelssohn, the central figure of the German Jewish Enlightenment, did as much as anyone to give Jewish emancipation a serious philosophical foundation. Mendelssohn’s Jerusalem (1783) is, in this respect, the most important Jewish political text of the eighteenth century.

Islam and other non-Christian traditions were familiar to Europeans mainly through scholarship, travel, and trade, and they became increasingly important as European contact with the Ottoman Empire, Persia, India, and China expanded. The fact that the Enlightenment was, in significant part, a project of European Christian self-reform, and that the encounter with non-Christian traditions was a minor and largely instrumental element of it, is a fact worth keeping in mind.

This religious diversity was the context within which the Enlightenment developed. The experience of religious conflict, and the search for principles of coexistence, was one of the central preoccupations of the period. Worth pausing on: the standard story of the Enlightenment as a victory of “reason” over “religion” badly misrepresents the period. Reason and religion were not, in the eighteenth century, the opposing camps that they have since become. The serious Enlightenment thinkers were working out the terms of a new relationship between the two, and the result is what we now call modernity.

The Method of Reason Applied to Religion

The most characteristic move of Enlightenment thought on religion was the application of the methods of reason to religious questions. This did not necessarily mean the rejection of religion; it meant the demand that religious beliefs, like all other beliefs, should be tested by evidence and argument.

The Limits of Reason in Religious Matters

Some Enlightenment thinkers were cautious about the use of reason in religious matters. They held that certain religious truths, although rationally indemonstrable, were nevertheless acceptable to a reasonable person on grounds of faith, sentiment, or tradition. This position was characteristic of moderate Anglicans, Lutherans, and many of the German Aufklärer. The most sophisticated version of the position is, perhaps, Locke’s Reasonableness of Christianity (1695), which argued that the core of Christian doctrine is rational but that the detailed theological elaborations of orthodoxy are not; Locke concluded that Christianity is, in its essentials, a reasonable religion, and that the elaborate dogmatic systems of the churches are accretions that the early Christians would not have recognized.

Others were more aggressive. They held that any religious belief that could not be supported by reason should be rejected, and that traditional Christianity, with its miracles, prophecies, and dogmas, was a form of superstition that should be exposed and overcome. This more aggressive position was characteristic of French materialists, English deists, and the radical wing of the German Aufklärung. D’Holbach’s Système de la nature (1770) and La Mettrie’s L’Homme machine (1747) are the strongest versions of the position; they were also the books that were most carefully suppressed.

Miracles and Natural Order

The question of miracles was a central issue. The new natural philosophy, with its emphasis on the regularity of the natural order, called into question the credibility of miracle stories. The sun should not stand still in the sky, the dead should not rise from their graves, the laws of nature should not be suspended at the request of priests or prophets.

Hume’s Enquiry Concerning Human Understanding (1748) contained a famous argument against the credibility of miracles. Hume argued that the evidence for the regularity of nature was so overwhelming that no amount of testimony in favor of a particular miracle could outweigh it. The argument has been debated ever since, and it remains one of the most influential statements of the skeptical position. The argument is also, in a way that is sometimes not noticed, a striking exercise in Bayesian reasoning: Hume is, in effect, asking how much testimony for an extraordinary event would be required to outweigh the probability of the event given the background regularity. The argument has not been refuted; it has also not been universally accepted, even by people who think it correct. (Plantinga’s modal version, in God, Freedom, and Evil, is the most discussed twentieth-century reply; it works only on a particular conception of probability.)

Prophecy and Biblical Criticism

The new methods of historical criticism were also applied to the Bible. Spinoza’s Theological-Political Treatise (1670) applied the methods of rational criticism to the text of the Hebrew Bible, treating it as a historical document written by identifiable authors in particular circumstances. The Tractatus was published anonymously; Spinoza was widely suspected of being the author; the book was put on the Index in 1678, and remains the foundation of modern biblical criticism, even if it has been supplanted, in many of its details, by the historical work of Wellhausen, Graf, and the German school. Richard Simon (1638–1712), a French Oratorian priest, developed the methods of biblical criticism further, and was immediately suppressed by his own order. Johann Salomo Semler (1725–1791), a Lutheran professor at Halle, distinguished between the “religion” of the Bible and its “Scripture” — the latter being a human, historical document with a complex textual history. By the late eighteenth century, the field was an established part of European scholarship.

This development had important religious as well as intellectual consequences. If the Bible was a historical document, it could be subjected to historical criticism, and the textual foundations of Christian belief became more complicated than they had been in traditional theology. The complication was, in the long run, the source of both modern historical theology and modern atheism. The traditional Christian did not have to give up belief in the Bible; he did have to give up the belief that the Bible could be read apart from history. The conventional Christian reader, in the twenty-first century, lives in the world that the Enlightenment historians of the Bible made possible, whether he knows it or not.

The Varieties of Enlightenment Religious Thought

The religious thought of the Enlightenment was not a single thing. It included a wide range of positions, from devout Christianity to radical atheism. The following are the most important. Notice how the standard narrative — “Enlightenment = secular, religious = anti-Enlightenment” — does not survive a close look at the actual writers.

Deism

Deism was the most characteristic religious position of the Enlightenment, and the basic elements of the deist position are surveyed in Deism vs. Atheism. The deist accepted the existence of God and the existence of a moral order, but rejected the special status of any particular religious revelation, the authority of any particular church, and the credibility of miracles. God, for the deist, was a kind of cosmic designer who had created the universe, set its laws in motion, and then withdrawn to let it run.

The deist position was held by Voltaire, Franklin, Jefferson, and many others. It had the advantage of being compatible with the new natural philosophy (it could accept the argument from design) while rejecting the more miraculous elements of traditional Christianity. It also had the advantage of providing a basis for religious toleration: if no particular church had a privileged access to truth, then all churches (and all religions) deserved equal respect. Deism is, in many respects, a more successful Enlightenment position than has been recognized. The deist writers sold very well; the more radical materialist works were suppressed. The actual reading public of the eighteenth century was, in religious matters, more conservative than the philosophes, and the deist writings gave it a respectable form of religious minimalism that could be combined with traditional piety.

Natural Religion

Closely related to deism was the doctrine of natural religion, the idea that there were certain religious truths accessible to human reason independently of any particular revelation. These truths — the existence of God, the immortality of the soul, the obligation to virtue — could be discovered by the proper use of reason, and they formed a kind of rational core that was common to all religions.

The doctrine of natural religion was important in the late seventeenth and eighteenth centuries. It was championed by writers such as Samuel Clarke, William Wollaston, and the Earl of Shaftesbury, and it provided a framework for thinking about religion that did not require commitment to any particular confession. The Boyle Lectures, founded in 1692 and delivered annually at St Martin-in-the-Fields for more than a century, were the most important institutional vehicle of natural religion in England; they constitute, in their collected form, the most sustained defense of natural theology in the English language. The natural-religion tradition was, in fact, the dominant religious philosophy of the eighteenth-century British establishment, and it is more important than the deist camp in particular.

Rational Christianity

Some Enlightenment thinkers tried to construct a rational Christianity, stripped of miracles, prophecy, and dogmatic complexity. The most famous example was the English theologian John Locke, whose Reasonableness of Christianity (1695) argued that the core of Christian belief was simple and rational, and that the elaborate theological systems of the churches had been a corruption of the original message. Locke’s argument is more radical than it sounds: if the core of Christianity is simple, then the elaborate dogmatic theology of the orthodox churches is a human addition, and the authority of the priestly class that maintains it is illegitimate.

In Germany, similar projects were undertaken by the Neologians, a group of Protestant theologians who attempted to reinterpret Christian doctrine in the light of Enlightenment rationalism. The most famous was probably Johann Salomo Semler, who distinguished between the “religion” of the Bible and its “Scripture” — the latter being a human, historical document with a complex textual history.

Mysticism and the Heart

Not all Enlightenment responses to religion were rationalist. The German theologian and philosopher Friedrich Schleiermacher (1768–1834), often regarded as the founder of modern liberal Protestantism, argued in his On Religion: Speeches to Its Cultured Despisers (1799) that the essence of religion was not belief in propositions but a feeling of absolute dependence on the infinite. Schleiermacher’s work was important precisely because it tried to defend the legitimacy of religious experience against both rationalist criticism and supernaturalist dogmatism. Schleiermacher’s speech was itself a remarkable piece of rhetoric, addressed to an audience of cultured Berlin skeptics who, he was convinced, were not nearly as far from religion as they thought they were.

Similar themes can be found in the works of the English poet and clergyman William Law (1686–1761), the French mystic Madame Guyon (1648–1717), and many others. The Enlightenment was not only a rationalist movement; it was also a movement that produced serious attempts to defend the legitimacy of religious experience in a critical age. The standard history of the period still understates the persistence of the mystical tradition, perhaps because the mystics were, almost by definition, not as easy to fit into a narrative of progress.

Materialism and Atheism

A small but influential minority of Enlightenment thinkers embraced materialism and atheism. The French philosophers Julien Offray de La Mettrie (1709–1751), Baron d’Holbach (1723–1789), and Claude Helvétius (1715–1771) developed systematic materialist accounts of human nature that left no room for the soul, God, or the afterlife. D’Holbach’s System of Nature (1770) was the most comprehensive statement of this position. The book was published anonymously, as was required; it was publicly burned by the Paris hangman; it sold widely; it was one of the most widely read philosophical works of the 1770s. The actual readership of D’Holbach is, by the standards of the period, astonishing; the salon at which most of the materialists met, in D’Holbach’s own house, was the principal gathering place for the Parisian radical intellectuals of the 1770s.

Materialism was a scandal to most eighteenth-century readers, and it provoked fierce criticism from religious and political authorities. But it was a real and persistent current in Enlightenment thought, and it had an important influence on the development of modern secularism and naturalism. The interesting historical question is not whether the materialists were right but why they were so few. The number of committed materialists in late-eighteenth-century Paris can probably be counted on the fingers of two hands. Their intellectual influence was disproportionate; their social influence was negligible.

The Political Dimension: Toleration and the State

The political consequences of Enlightenment religious thought were at least as important as the philosophical ones. The religious settlement of the Enlightenment was the foundation of the modern secular state.

The Case for Toleration

The case for religious toleration had been developed in the late seventeenth century by writers such as John Locke, Pierre Bayle, and the anonymous author of the Letter Concerning Toleration (often attributed to Locke). The basic argument was that the state had no business using force in matters of religious belief, and that religious differences should be settled by persuasion rather than coercion.

The arguments for toleration combined several elements. There was a prudential argument: the attempt to enforce religious uniformity had produced the wars of religion, and the only way to prevent their recurrence was to allow different groups to worship in their own ways. There was a moral argument: religious belief was a matter of conscience, and forcing people to act against their conscience was a violation of their natural rights. There was a religious argument, advanced especially by Protestant writers: the true church was a community of the faithful, and coercion was incompatible with the nature of Christian community.

The case for toleration was also developed from skeptical premises. Bayle’s Philosophical Commentary on These Words of the Gospel (1686) argued that even if it could be shown that one religion was true, the use of force to impose it was still illegitimate, because sincere belief could not be compelled. The skeptical case for toleration became increasingly important in the eighteenth century, and it is, in fact, more powerful than the prudential case; the prudential case concedes that some religions are false and toleration is the lesser evil, while the skeptical case concedes nothing and treats toleration as a positive good.

The Limits of Toleration

The Enlightenment case for toleration had significant limits. Locke excluded Catholics and atheists from the scope of toleration, on the grounds that Catholics owed allegiance to a foreign power and atheists could not be trusted to keep their promises. The French philosophes were more generous, but they were also sometimes inconsistent, and their commitment to toleration was not always extended to religions they found particularly offensive, such as Islam or Judaism. Voltaire’s remarks on Judaism, in particular, are embarrassing to a modern reader; they are also typical of the period.

The full extension of the principle of toleration to all religious groups was a long process that continued well into the nineteenth and twentieth centuries. The Test and Corporation Acts were repealed in Britain in 1828; Catholic emancipation was achieved in 1829; Jewish emancipation in 1858. The contemporary principle of religious freedom, as enshrined in international human rights documents, is a much broader and more demanding ideal than the eighteenth-century versions of it, and the fact that the ideal is still not realized in many parts of the world is a measure of how much work remains.

The Separation of Church and State

The political implication of the case for toleration was the separation of church and state. In countries with an established church, the establishment itself was challenged; in countries without an established church, the legal disabilities imposed on non-conformists were gradually removed.

The American Constitution, with its First Amendment prohibition on the establishment of religion, became the most successful model of the separation of church and state. In France, the Revolution of 1789 abolished the privileged position of the Catholic Church, confiscated church property, and attempted to replace Christianity with a new civic religion of reason. The National Assembly’s “Constitution civile du clergé” (1790) and the subsequent de-Christianization campaign of 1793–94 were the most ambitious attempts at the political reorganization of religion in the modern period. These measures were partly reversed after the Revolution, but the principle of laïcité remained a central feature of French political life, and the long argument about what laïcité means — strict separation, or the more elastic neutrality of the contemporary French state — is itself a continuation of the Enlightenment argument.

The Critique of Organized Religion

One of the most characteristic features of Enlightenment religious thought was the critique of organized religion, especially the Catholic Church and the more institutionalized forms of Protestantism.

The Church as Political Power

The Catholic Church was a major political power in eighteenth-century Europe. It owned vast estates, ran its own courts, censored publications, and maintained a network of religious orders that operated independently of secular authority. The philosophes saw the Church as one of the main obstacles to the rational reform of society, and they devoted enormous energy to attacking it.

Voltaire’s Philosophical Dictionary (1764), the Encyclopédie’s many critical articles, and countless pamphlets and satirical works subjected the Church to a sustained and often savage critique. The Church was portrayed as a force of superstition, intolerance, and political reaction, and its privileges were attacked as inconsistent with the rights of citizens. The critique was, in many of its particulars, exaggerated. The Church in 1760 was not what it had been in 1500; the Jesuits had been expelled from Portugal, France, and Spain in the 1750s and 1760s; the Index was losing its bite; the Counter-Reformation was, intellectually, a spent force. The critique was, however, more right than wrong. The Church of the ancien régime was, in the last third of the eighteenth century, a political power that was structurally unable to reform itself, and the revolutionary assault on it was the predictable consequence of its long resistance to reform.

The Critique of Clericalism

Beyond the specific attack on the Catholic Church, the Enlightenment critique of organized religion also extended to the broader phenomenon of clerical power. The idea that priests, ministers, and rabbis should have special authority over matters of belief and conscience was challenged by the claim that every individual had the right and the responsibility to judge matters for themselves.

This anti-clericalism was not uniformly hostile to religion. Many Enlightenment thinkers were willing to admit that religious institutions could play a positive social role, providing education, charity, and moral guidance. But they were uniformly opposed to the idea that religious authorities should have the power to dictate to the state or to override the judgments of individual reason. The position is, in fact, the foundation of modern secularism; it is also, in its structure, recognizably Protestant — the priesthood of all believers, taken to its political conclusion.

The Critique of Religious Intolerance

The most powerful critique of organized religion was the charge of intolerance. Throughout the eighteenth century, examples of religious persecution — the expulsion of Protestants from France after the revocation of the Edict of Nantes in 1685, the persecution of Jews in various parts of Europe, the trial of the Protestant Jean Calas in Toulouse — were widely publicized and used as evidence of the dangers of clerical power.

Voltaire’s campaign on behalf of Calas, and his broader campaign against religious intolerance, helped to make the principle of toleration a central cause of the European Enlightenment. The political campaigns for Jewish emancipation, for the rights of religious dissenters, and for the abolition of religious tests for public office were all closely connected to the broader Enlightenment project of religious freedom. The campaigns were, in fact, remarkably successful; the legal disabilities under which religious minorities had labored were, in most of Western Europe, abolished by the middle of the nineteenth century. That this success has been so thoroughly forgotten in our present debates about religious freedom is one of the more striking features of contemporary political memory.

The Long-Term Consequences

The long-term consequences of Enlightenment religious thought are difficult to summarize. The Enlightenment was the source of modern secularism, and the decline of religious belief in modern Europe is in part a consequence of the kind of thinking that the Enlightenment promoted. But the Enlightenment also made possible the modern defense of religious freedom, the separation of church and state, and the development of a more reflective, critical, and intellectually serious kind of religious thought.

The Rise of Modern Liberal Religion

The Enlightenment critique of traditional religion made possible the rise of modern liberal religion, with its emphasis on individual interpretation, the historical study of sacred texts, and the accommodation of religious belief to the findings of modern science. The great Protestant theologians of the nineteenth century — Schleiermacher, Hegel, the Ritschlian school, the Niebuhrs, Tillich, and Bultmann — were all, in their different ways, working out the implications of the Enlightenment critique of traditional theology.

Liberal Judaism, liberal Catholicism, and the various modern expressions of religious thought are also descendants of the Enlightenment, even when they include important elements of resistance to it. The Second Vatican Council (1962–1965) is, in many respects, an event in the long history of the Catholic Church’s belated engagement with the Enlightenment; the document Nostra aetate (1965), with its repudiation of the charge of collective Jewish responsibility for the death of Christ, would have been impossible without the prior Enlightenment critique of traditional Christian antisemitism.

The Persistence of Traditional Religion

The persistence of traditional religion in the modern world is also a feature of the legacy of the Enlightenment. The Enlightenment project of discrediting religious belief was, in retrospect, a failure. The great majority of human beings continue to profess some form of religious belief, and in many parts of the world, traditional religion has experienced a powerful revival. The “secularization thesis” — the idea that modern industrial society would necessarily produce a decline in religious belief — has not survived contact with the historical evidence. The United States is the most religious large industrial society; the most secular parts of Europe are the most thoroughly post-Christian, but the post-Christianity is itself a long, slow process that began in the eighteenth century and has not yet reached its conclusion.

The contemporary situation is thus a complex one. The principles of religious freedom and the separation of church and state, both products of the Enlightenment, are widely accepted. But the substantive critique of religious belief, which was also a feature of the Enlightenment, has not produced the secular utopia that some of its advocates expected. The expectation of a secular utopia was, in fact, an Enlightenment expectation; the failure of the expectation is one of the more chastening features of the long history of the period.

The Dialogue Between Religion and Modernity

The contemporary dialogue between religion and modernity is a continuation of the dialogue that the Enlightenment began. Religious thinkers have had to come to terms with the findings of modern science, the methods of historical criticism, the principle of religious freedom, and the moral demands of pluralism. Secular thinkers have had to come to terms with the continuing vitality of religious belief, the importance of religious communities, and the difficulty of providing a comprehensive secular account of the human condition.

The Enlightenment did not resolve these questions. It opened them up, and it provided the vocabulary and the conceptual framework within which the contemporary debate continues to be conducted. The fact that the debate continues is, perhaps, the most useful sign of the inheritance.

Conclusion

The relationship between the Enlightenment and religion was complex, contested, and ultimately transformative. The Enlightenment was not a uniformly anti-religious movement, but it did mount a serious critique of many features of traditional religion: the authority of churches, the credibility of miracles, the validity of biblical prophecy, and the political power of clerical institutions. It also produced a powerful defense of religious freedom and the separation of church and state, principles that have become central to modern political life.

The religious thought of the Enlightenment remains a vital resource for thinking about the relationship between faith and reason, the role of religion in public life, and the conditions of coexistence in a pluralistic society. To engage with it is to engage with one of the most consequential and contested questions of the modern world. The fact that the question is still contested is, perhaps, the most useful sign that the Enlightenment is still alive.