The Enlightenment, Naturalism, and the Secularization of Values

Alan Charles Kors

The most influential contribution of the Enlightenment to modern thought, after its transformation of religious toleration from a negative to a positive value, was the secularization of ethical debate. Historically, however, it would be one-dimensional—indeed wrong—to understand this phenomenon as the product of a virgin birth of ideas in the Enlightenment. Both deistic and atheistic Enlightenment authors were part of the same world of thought. Similarly, both eighteenth-century Christian and Enlightenment thinkers were heirs to the same conceptual revolution of seventeenth-century natural philosophy (which included what we now term science), and both moved on the same deeper tidal currents of early-modern intellectual change.

The seventeenth century produced a flowering of deep theological thought, and, indeed, it was the high-water mark of European demonological belief and persecution. It also created the “new philosophy” that was so dramatic an agent of historical change. The new philosophy involved a rejection of the presumptive authority of the past and an experimental and often mathematized model of natural knowledge. This new philosophy, as it indeed was called, emerged within a deeply religious culture. Its unintended consequences, however, would create an increasingly secularized culture in terms of scientific and ethical belief. At the heart of this were the fruits of the systematic study of nature.

How, then, did the religious intellectual community contribute to the formation of the Enlightenment mentality? Above all, the revolution in seventeenth-century natural philosophy radically transformed the culture’s sense of nature and its relationship to divine providence. As we shall see, that transformation made it increasingly possible for thinkers to dispense with theological justification in ethical debate and to refer to nature alone.

The seventeenth-century natural philosophers who had broken from the scholasticism and the authorities then dominant in the universities of Europe believed that their inquiries revealed ordered laws of nature, with God as lawgiver. The laws of nature were seen more and more as embodiments of the will of God, agents of his wisdom and purpose. The laws of nature, in such a view, were admired for accomplishing the intentions of God without need of further intervention. For the seventeenth-century experimental and quantitative philosophers, their work was not constructing a view of nature but discovering laws of nature that had been there for the duration of the universe.

Johannes Kepler, in announcing his third law of planetary motion, proclaimed the belief that he was the first human being to gaze upon God’s handiwork with understanding. He had found what God had done. Indeed, how could thinkers not believe that they had found the order, providence, and craft of God in the discoveries we still call “the scientific revolution”: Kepler on planetary motion; Galileo on mechanics and motion; Harvey on the circulation of the blood; Gilbert on magnetism; Torricelli on air pressure and the vacuum; Boyle on pneumatics; Huygens on the pendulum and centrifugal force; and, above all, Isaac Newton on motion, optics, and universal gravitation? When Alexander Pope penned the epitaph for Newton, he spoke for an age: “Nature and Nature’s laws lay hid in night / God said ‘Let Newton be!’ and all was light.”

Before the new philosophy of the seventeenth century, European thinkers had looked on the world of nature as sharply divided by the boundary between the heavens and the earth. In the physical heavens and the celestial bodies, there was regularity and order, though this was not expressed in terms of law: astronomy was the one dignified area of natural inquiry for a learned mind. Beneath the moon, however, chaos reigned: disorder, instability, and disharmony. God’s providence extended to the whole of the creation, but beneath the moon, it was above all in terms of His particular acts of will that He governed. The ongoing motions of the heavenly bodies alone seemed to bear the imprint of a more general providence. All of this changed in the aftermath of the seventeenth century.

There was, as a matter of historical fact, a religious awe in the new science, but it was one that located God’s providence far less in the history of miracles and prophecies and far more in the natural mechanisms around us. Indeed, without an initial religious wonder at the order of nature, European civilization would scarcely have been able to patronize, value, and extend the domain of natural explanation. Such a change in understanding, however, beyond any conscious desire of most natural philosophers to alter their culture in theological terms, made possible a reconceptualization and revaluation of nature with profound implications for religion, for thinking about human nature, and for ethical theory.

For the new philosophy, it was the mechanisms and laws of the natural order—including those of human nature—that embodied divine will, such that following the empirically discernible laws of nature meant following the laws of God. If the two were equated in any way, however, one safely and reasonably could think of human nature solely in terms of the commonly accessible natural order alone without theological fear or condemnation. As the great (and pious) scientist Robert Boyle put it in his Experiments Physico-Mechanicall (1660), “God gave motion to matter, and in the beginning . . . the various motions of the parts of it, as to contrive them into the world he designed they should compose.”

This change was most dramatic in moral philosophy. It always had been a commonplace of Western thought to say that human beings, like all animals, sought pleasure and fled pain. There were profound distinctions, however, among genres of pleasure: beatitudo (eternal bliss); delectatio (delight); voluptas (sensual pleasure); and felicitas (worldly happiness). Aquinas and almost all traditional Christian moral theology argued that the pursuit of felicitas was a simulacrum—a pale, corrupted shadow, and a false resemblance—of our original desire for the highest good and highest happiness, beatitude. It was what remained after the Fall. Given the distance between the goal of earthly happiness and the goal of union with God, being governed by the pursuit of natural, secular pleasure and the flight from natural, secular pain was far removed from Aquinas’s discerned end of the human quest for beatitude and in that sense was even the mark of our sin and our distance from God. Our effort to secure earthly pleasure and to avoid earthly pain provided subject matter for countless sermons: it was the sign of our depravity and bestial state. To the extent that it ruled our lives, it was the indication that we had not raised ourselves or been raised by God to a higher level of being. In pursuit of union with God, the Christian was expected to see earthly pleasures as trivial and, at times, dangerous distractions and to accept many of the burdens and pains of life as occasions of a closer relationship to God.

In light of the new philosophy of the seventeenth century, however, such an evaluation was quite thoroughly rethought. If it were, indeed, a law of nature that all living creatures, including human beings, sought earthly pleasure and fled earthly pain, then it followed that the pursuit of such pleasure was nothing less than the divinely ordained end of human life. What could be, in Jefferson’s later phrasing, more “self-evident”? The commonplace observation that we sought pleasure and fled pain now became an understanding of the very mechanism whereby the will of God was fulfilled. The pursuit of happiness was what God himself had chosen for us and, given that source, had surely joined to the good. If increase of natural pleasure and reduction of natural pain was God’s criterion for us, then the simplest route to a proper ethical understanding was to find in nature the real causes of human well-being and suffering.

John Locke’s influence upon the eighteenth century and the Enlightenment was virtually immeasurable. In the 1691 edition of his Essay Concerning Human Understanding (1690), he explicitly asserted (Book I, Chapter 3, Section 6) that God had harmonized the physical and moral worlds. Certain that moral knowledge (like all knowledge) was learned by experience, Locke concluded that the true and knowable causes of enduring human happiness, and, thus, of virtue, were identical to virtue. We could err, especially if we let our passions govern our lives without mediation by acquired knowledge, but over time our accumulated experience would lead us to the very knowledge we desired. Locke wrote, “Virtue [is] generally approved, not because innate, but because profitable.” There was an “inseparable connection” of “virtue and public happiness,” and virtue in behavior was “necessary to the preservation of society, and visibly beneficial to all with whom the virtuous man has to do.” Thus, a man naturally would choose to “recommend and magnify those rules to others, from whose observance . . . he is sure to reap advantage to himself.” Whether from conviction or self-concern, he naturally would term “sacred” those values “which, if once trampled on and profaned, he himself cannot be safe nor secure.” Cherishing the values essential to well-being did not depend upon believing in their religious origin, “since we find that self-interest, and the conveniences of this life, make many men own an outward profession and approbation of them, whose actions sufficiently prove that they very little consider the Lawgiver that prescribed these rules.”

Thus, while it might have mattered philosophically to Locke and many of his disciples that the pursuit of happiness arose from the will of God, in practice that recognition was in no way necessary for finding virtue. That pursuit could be accomplished in terms of our natural desire to preserve society and provide benefits to ourselves and to all humankind.

Denis Diderot
Denis Diderot

Locke’s model of the empirical discernment of nature’s mechanisms, however, was not the only influential version of locating the “nature” given to things by God. For some, “natural” meant the statistical norm. It was “natural” for mothers to love their offspring and “unnatural” for them to abandon them; “natural” to be between five and six feet tall, but “unnatural” to be three or seven feet tall. For others who were still influenced by a long tradition of Western thought, the “nature” of a being was that which distinguished it from all other beings—its essence. Triangles might share many qualities with other polygons, but triangles, by their nature, were polygons with three sides, the sum of whose interior angles was 180 degrees. That was the essence of a triangle as opposed to all other entities. Human beings possessed reason and moral knowledge, which made them uniquely human whatever other traits they shared with other beings.

The naturalization of values deeply affected even the most pious Christian ethical thinkers. The profoundly influential moral philosopher Joseph Butler, bishop of first Bristol and then Durham and confessor to the Queen of England, was a naturalizing essentialist. In 1724, his Fifteen Sermons on Human Nature were published to almost universal acclaim in the Protestant English establishment and condemned only by a handful of evangelical preachers then considered marginal to polite society. There he argued that God clearly had given us a distinct human nature—reason and moral sense—and a desire for happiness, which always motivated us.

Thus, Butler argued that before and wholly independent of Christian revelation, natural knowledge and the ordinary tendencies of our human nature led us to virtue if instead of being irrational and impulsive we mediated our pursuit of happiness by our true human nature. If we pursued happiness merely by appetite, as was the case with beasts, we would obtain neither happiness nor virtue. To enter this historically significant way of thinking, imagine a human being with extreme thirst coming to a pond surrounded by animal skeletons. Where an animal would drink by appetite, a human, endowed with reason, should infer the toxicity of the water and not yield to thirst. Similarly, a hungry animal would take food by force from the young or from any weaker being, which we would not condemn morally. A human being, however, endowed with a sense of shame, should restrain appetite in a similar circumstance, as in the case of sexual appetite and rape. If he did not, we would consider him bestial, and we would condemn, punish, and scorn him for the failure to be human.

For Locke and Butler, then, it was empirically true that those who acted without reason or moral awareness did not achieve happiness. The impulsive person came to grief. The thief, cheat, scoundrel, or otherwise immoral person was unloved, distrusted, and alone. Those who asserted that the immoral were happiest had never made a true survey of human life.

In the work of Locke and Butler, the informed pursuit of secular happiness led us to moral excellence. They argued, against both Calvin and Hobbes, that self-love was good and not in conflict with benevolence. Would one truly want someone who did something benevolent to feel sad instead of glad about it? In Butler’s words (and he was reviled for such views by evangelicals such as John Wesley): “The thing to be lamented is not that men have so great regard to their own good or interest in the present world, for they have not enough.” There was no inconsistency between moral duty and self-love or self-interest, “what is really our present interest—meaning by interest happiness and satisfaction.” Indeed, “self-love then, though confined to the interests of the present world, does in general perfectly coincide with virtue, and leads us to one and the same course of life.” The only Christian dimension, in Butler’s fifteen sermons, was that the achievement of happiness through virtue was reinforced by the particular command of Christ and, for those who did not recognize their true interest, by the fear of hell. As with Locke, the link to God may have been of paramount importance to Butler, but once our moral values were deemed discernable from the secular pursuit of happiness, the easiest route to them would be the study of human nature and the dynamics of the human condition.

The anti-Christian deists of the eighteenth century thus did not invent the equation of worldly happiness and virtue, but they dramatically naturalized the religious component of the pursuit of happiness categorically. Matthew Tindal, England’s most influential and most widely read deist, in his Christianity as Old as the Creation (1730), made the universal laws of nature, including the human pursuit of natural pleasure and avoidance of natural pain, the sole moral nexus between mankind and God. God required nothing and thus had created us for our well-being alone. Now we had a criterion for judging even supposedly religious commands, because “it unavoidably follows: nothing can be a part of the divine law, but what tends to promote the common interest and mutual happiness of his rational creatures.”

This being the case, Tindal wrote dramatically, we could dismiss an ethic of denial and suffering: “God can require nothing of us, but what makes for our happiness . . . [and] can’t envy us any happiness our nature is capable of, [and] can forbid us those things only which tend to our hurt.” The “desire of happiness” was rightfully “the principle from which all human actions flow.” Ironically, in Tindal’s work, so influential both in Britain and France, the neglect of secular happiness now was blasphemous.


Tindal’s title was a prudent one (implying the eternity of Christian truth), but it offered him only legal, not intellectual, protection because virtually all of his readers understood that he was asserting that Christianity had added nothing that was not or could not be known from the study of nature. His work became known as “the Bible of deism,” and it elicited a torrent of refutations, quoting and explaining his scandalous views, which attracted yet a larger audience for his book and a larger acquaintance with his arguments.

By far, however, this naturalization and secularization of values found its most prominent expression in the French Enlightenment, whose widely read authors and texts changed the nature of Western thought. French became the lingua franca of educated Europe in the eighteenth century, and the major figures of the Enlightenment were celebrated in reading circles and in courts from Britain to the Germanic states to Russia. By the middle of the eighteenth century, there emerged in Paris and the provincial cities a community of thinkers and writers who shared common attitudes toward the new philosophy, arbitrary authority, and the church. They saw themselves as part of a “Republic of Letters” that, in their minds, stood between a sad past of superstition, despotism, ignorance, and suffering and a possible future of Enlightenment in which—free of the presumptive authority of the past, educated by experience methodically gathered and tested, and applying knowledge toward the end of reducing human suffering and increasing human well-being—the human species would rewrite its relationship to the natural and social world. It is a remarkable moment of the history of human consciousness—this generation that thought of itself as leading Europe from a phantasmagoric past into a world closer to the heart’s desire for happiness.

Diverse in social and educational origin but bright, sociable, and recognizing each other by common values, interests, and opponents, the philosophes, the philosophers of the French Enlightenment, coalesced around certain institutions—cafés, salons, academies—and around certain ideas. By mid-century, they developed a sense of community with purpose, coming to recognize the importance of their rejection of inherited authority per se and their commitment to empirical evidence, rational analysis, and nature as the sole source of knowledge and values and, from that, a commitment to the principle of utility—that the happiness of the species was the highest value and that all things might be judged by their contribution to happiness or suffering.

Their commitment to these values, and their competition with the clergy for the role of educator of their society, led the philosophes into fundamental conflict with the Roman Catholic Church in France, a struggle that was one of the defining characteristics of the French Enlightenment. Combating the Church over issues of tolerance and censorship, and offering quite different histories and analyses of their societies, the philosophes came to identify the Church (and the Church the philosophes) as their antithesis, their deepest foe. Their rejection of traditional authority and supernatural claims and their espousal of secular need as the highest value led the community of philosophes to see the Church as the epitome of arbitrary traditional authority, antisecularism, and anti-utilitarianism, and because of its powers of censorship, persecution, intolerance, and monopoly of most education, as the greatest barrier to the future they desired to bring into being. Anticlericalism was the most common denominator of the Enlightenment. Primarily deistic, it believed that God spoke to mankind through nature and nature alone and that the priests had usurped and falsified God’s voice in sectarian religions.

The great propagator of the Enlightenment worldview, though prudently toned down for legal publication, was the vast project of the Encyclopédie, published, essentially under the editorship of Denis Diderot, in twenty-eight volumes between 1751 and 1772. It was a runaway best-seller—remarkably so—and was frequently sold in pirated editions throughout Europe.

The Encyclopédie engaged over 160 writers and possibly another hundred informal consultants, drawing into its orbit and its frame of reference the expertise and scholarship of lay (and occasionally even clerical) France. Its tone was set by a Discours préliminaire (Preliminary Discourse), published in 1751 by the celebrated mathematician (and briefly coeditor) Jean Le Rond d’Alembert. He argued that the seventeenth century had effected a rebirth of knowledge and a qualitative change in the acquisition of knowledge. Knowledge, he urged, in the spirit of his seventeenth-century hero Francis Bacon, was a human power to understand nature and to alter what could be altered closer to the human heart’s desire for happiness. At the heart of that recent renaissance, for d’Alembert, was the rigorous empirical and experimental method of the best of seventeenth-century natural philosophy.

The Encyclopédie provided a focus and means of diffusion for the perspectives, scholarship, science, and analyses of the new philosophy. In article after article, it expressed or implied its vision of questioning the origins and foundations of all authorities, beliefs, and institutions; of intellectual progress; and of the dynamism of science, technology, and secular inquiry.

Frequently attacked and occasionally suppressed, it drew its authors, experts, and readers into the experience and human drama of censorship, and it found agents of collusion and support in the highest structures of the old regime: the courts, the aristocracy, and the ministries of the monarchy. Its very existence as well as its contents were corrosive to the sacred idols and established intellectual authorities of its culture, and it played a major role in establishing the consciousness of this movement that more and more came to call itself “the party of humanity” or “the party of reason.” That party’s criteria of truth were not claims of special authority or revelation, but the reason and experience of natural lights explained for all to see, replicate, analyze, and judge. Knowledge was communicable and conformable, requiring no occult mysteries and privileged interpreters. Its goal was not despotic power but rather utility: the happiness, self-preservation, and flourishing of the human race. That was their self-image and, increasingly, it was their image in a culture in which they were winning the war for public opinion.

The Enlightenment was not without its severe internal debates, but the culture recognized its heart in its claim that so much of existing authority—intellectual, religious, political, social, and ethical—was arbitrary and arose from power and tradition alone. The Enlightenment did not assail authority per se, but arbitrary authority, and in countless works it called upon authority in all domains to justify itself. Justification, of course, demanded criteria. What were the criteria of the Enlightenment?

First, and above all, claims had to be made and supported solely in terms of natural experience. The Enlightenment was explicitly Lockean in the most fundamental sense of Locke’s epistemology (his theory of knowledge). All real knowledge ultimately arose from experience of the natural world, which meant that claims of knowledge were not based on social or ecclesiastical position or on occult interactions but were communicable and verifiable in the medium of natural phenomena. This ruled out supernaturalism for French Enlightenment thinkers. If our knowledge arose solely from natural experience, then it was bounded by and limited to that natural experience and what could be inferred from it. As early as 1733, in his Philosophical Letters from England, Voltaire had explained Locke to his French audience by noting that for more than a millennium, philosophers had argued about the substance of the soul, about what underlay our experience. Like Locke, Voltaire averred that the task of the natural philosopher was not to know the unknowable essence of the mind—a quest that had led to more than a thousand years of disagreement without any possible consensus—but to study its behavior, which indeed could be known by experience. As to the metaphysical issue of the nature of the soul, Voltaire proclaimed that he was proud to be as ignorant as Locke.

The greatest figures of human history, Voltaire concluded, were not murderous warriors and tyrannical kings, but those thinkers who had given human beings an accurate and useful sense of both the powers and the limits of their capacities—Newton, not Caesar; Bacon, not Alexander; Locke, not Tamerlane. The authorities maintained that philosophers were a grave threat to social order, but Voltaire insisted that philosophers thought and argued in peace while “it is rather the theologians, who, having first had the ambition of becoming heads of a sect, soon came to have that of becoming heads of a faction” and sowed discord among mankind.

In the view of Enlightenment thinkers, if moral knowledge were rightly limited to natural knowledge, which clearly disclosed an ineluctable human desire for happiness, then it followed that utility, most broadly defined as an increase in well-being and a decrease in suffering, was the criterion to be applied to the issues of how we should live together. Such a criterion, however, to say the least, was not unproblematic, and the debates its application entailed are with us still. Should we think of happiness in terms of individuals or in terms of the larger society? To what extent was happiness physical or psychological? Was there a happiness to virtue or benevolence itself?

Enlightenment thinkers indeed differed in definitions of happiness and lacked precision in specifying the application of the criterion. In general, however, they held to certain common notions whose influence remains forcefully with us. First, they believed that without solving the problem of social cooperation, however achieved, the species was doomed to unhappiness. Second, they believed that despotism—subjecting the lives of individuals to the arbitrary will of wielders of power—always led to misery. Third, they believed that freedom of thought was a sine qua non of human progress, both as a manner of being human and in terms of the increased mastery it brought over of the causes of our well-being or suffering. Fourth, they believed that toleration was an indispensable—perhaps the most indispensable—route to human well-being. All of these themes, for them, were interrelated.

These notions were set early in the French Enlightenment and strengthened as the century progressed. Enlightenment thinkers were acutely aware of the astonishing diversity of human societies and values, but they understood full well that this diversity occurred within a world of natural consequences. Early on, in his Lettres persanes (Persian Letters, 1721), Montesquieu told his parable of the Troglodytes. At first, the tribe sought to pursue happiness by vicious means, with no thought by any individual about the well-being of others, but their vice brought them only anarchy, misery, and death. The virtuous Troglodytes who survived them, on the other hand, sought happiness without government by means of virtue, mutual concern, cooperation, and honesty; and they achieved a blissful life (until, at the height of prosperity, they sadly traded the burden of self-government for monarchy). One generation after the French coercively had rid the realm of most Protestants, one of Montesquieu’s Persian characters wrote of the good fortune of the Persians in refusing to cede to the clergy’s desire to banish Christians from Islamic lands, given the benefits they brought to that society. When a Frenchman discovered that the main protagonist was from Persia, he asked, betraying his parochialism, “But how could anyone be a Persian?” The main Persian protagonist was sensitive to despotism everywhere in Europe but not in his own life, where his power over his cloistered wives was absolute. Absence reduced the fear by which he ruled there, however, and, as his favorite wife wrote in a final letter as she betrayed him, the voice of nature had replaced his rule. Did you truly believe, she asked, that I was made to serve you?

There was a cosmopolitanism to much of Enlightenment thought that fought against the European will to see all things in reference to their own place in the world. Montesquieu, throughout the Lettres persanes, emphasized the vanity of each nation judging things only through its own eyes. Voltaire, in his Histoire universelle (1753), did not begin with the Ancient Near East or the Greeks, but with China. He presented the Chinese empire as the first great civilization, attributing to them, before the Christian era, minted currency, fine fabric, the invention of paper, printing, porcelain, clocks, gunpowder, distance navigation, and astronomical instruments, which he noted they developed a thousand years before Julius Caesar lived. (He attributed the Chinese decline vis-à-vis Europe to excessive devotion to tradition and to the complexity of their written language.) Diderot, in his Supplément au Voyage de Bougainville (Supplement to Bougainville’s Voyage, 1772), created a fictionalized Tahitian sage who, as the islanders bid farewell to the first French to land there, bemoaned the fate that awaited Tahiti. The Europeans would return, he warned, to impose their religion, to make the Tahitians feel guilty and criminal about their natural sexual practices, and to tyrannize them. With the advent of the Enlightenment, the West began to engage the rest of the world in other than missionary terms.

In Voltaire’s Philosophical Letters, it was England that provided the contrast to arbitrary French society and authorities. He campaigned for the English innovation of inoculation (who had taken it, he explained, from the Turks) against smallpox, suppressed in France both by a Faculty of Medicine that viewed the practice as a violation of the Hippocratic Oath and by a Faculty of Theology that saw the practice as man playing God. He praised productive citizens and independent farmers who enriched their country while titled aristocrats lorded their status over everyone and crushed the peasantry under taxation from which the nobility was exempt. He praised the gifts gotten from a science unrestricted by theological censorship. Above all, Voltaire stressed the bounty and peace of a nation where citizens of all religions and backgrounds could work “for the benefit of mankind.” In an England that encouraged trade and commerce, he noted, Christian, Jew, heretic, and Muslim trusted each other’s word “and reserved the name of infidel for those who went bankrupt.” If there were one religion in England, he warned a France proud of its uniformity, there would be tyranny; if there were two, “they would cut each others’ throats.” But there were thirty, so they “lived happily and in peace.”

Indeed, the great issue and battle cry of the Enlightenment that united virtually all of its diverse tendencies and that won over public opinion was toleration. After two centuries of religious hatreds, persecutions, and wars that left Europe in exhaustion and in recoil from its own cruelties, the Enlightenment found its audience receptive to the claim that the intolerant always caused harm and that toleration always was a blessing. Voltaire—who was the first to hold a pen that indeed was mightier than any sword—spent more than four decades, with increasing fame and success, trumpeting the cause of toleration writ large and decrying the evils of intolerance. Human beings should be free of the oppression of civil and religious power. In the civil sphere, it was slavery that embodied the worst of a failure to understand the evil of not treating individuals as one’s fellow creatures. In Candide (1759), the hero and Cacambo meet a miserable, ill-clothed slave whose grinding work left him with only one arm and one leg. Voltaire, through him, spoke to his readers: “This is the price paid for the sugar you eat in Europe.” In his Traité de tolerance (Treatise on Toleration, 1763), he portrayed the horror of judicial murder due to religious intolerance and argued that it would be insufficient simply to claim that all Christians should cease their disputes and love each other. “I, however, am going further: I say that we should regard all men as our brothers. What? The Turk my brother? The Chinaman my brother? The Jew? The Siamese? Yes, without doubt.” When the innocent are victims of “error, passion, or fanaticism,” and when those who administer the law “can slay with impunity by a legal decree,” then the public can see “that no man’s life is safe.” When Salman Rushdie, under sentence of death for supposedly mocking Islam, emerged from hiding at his first press conference and was asked what he had done during that year, he said that he had been reading a great deal of Montesquieu and Voltaire.

The formula in Enlightenment thought, which remains of such great relevance to current debates around the world, was that if the pursuit of happiness and the reduction of pain were indeed the essential human motivations, then the only justification of the state, a creation of culture, was an implicit social contract to limit power to that end. There are moments in intellectual history when a book’s remarkable success arises from a culture’s recognition of what it has come to believe and to reject. In 1764, Cesare Beccaria published Dei delitti e delle pene (On Crimes and Punishments). It was quickly translated into French and English (and other major European languages) and became an international best-seller. For Beccaria, a deep admirer of Montesquieu, Voltaire, and other French Enlightenment authors, the only model of both government and society consistent with our knowledge of human nature was that they were formed by individuals sacrificing the least possible portion of their natural liberty in exchange for the beneficial security of a state that repressed crime and let them live in safety. From this followed a clear understanding of the legitimate ends and limits of government: the greatest happiness of the greatest number consistent with a minimal loss of individual liberty (a liberty itself essential to the pursuit of happiness).

All law and power, then, must justify itself by demonstrating that it secured the greatest happiness at the least cost of individual liberty. If laws did not secure that, they were unjust. With such a model, Beccaria sought to strip criminal codes of much of what dominated them in the eighteenth century, and in so doing he began a project of reform that, for many, is ongoing today. From such a wholly secular and natural understanding of society, there could be no victimless crimes, no religious crimes, and no penalties beyond the minimum punishment necessary to deter real crimes. Anything else was tyranny and cruelty. With vivid rhetoric, he sought the categorical elimination of theology and religion from the law (in the definition of crime and its severity, and in the determination of any punishment). All punishment, to be just, must be minimal and purposeful, which for Beccaria and so many of his Enlightenment readers eliminated torture in both interrogation and penalties, and the death penalty, since swift, fair, and certain justice was a far more effective deterrent than death. Because all citizens entered society to secure, not lose, their freedom to pursue happiness, the protection of the accused had categorical primacy. Because all citizens had sacrificed the same portion of natural liberty, there must be the strictest equality before the law. That agenda, of course, remains a work in progress. By naturalizing and secularizing moral and political values, the Enlightenment opened the door to distinctly modern debate.

Such debate accelerated at what were the boundaries of the Enlightenment, the categorical naturalism of the late French Enlightenment materialists and atheists, who included Julien Offray de La Mettrie, the Baron d’Holbach, Jacques-André Naigeon, and, most famously, Denis Diderot. Although in practice orthodox eighteenth-century thinkers disfavored spiritualist or supernatural explanations of natural phenomena, they remained wedded, in fundamental philosophy, to the view that matter, passive and inert, had acquired motion from an immaterial being (God) and that the source of its spontaneous motion (as in plant growth, animal behavior, or the voluntary movements of human beings) could only be immaterial (vegetable, animal, and human souls). In the case of vegetables and animals, spiritualist explanations of specific physical behavior increasingly came to be seen as an admission of ignorance. In the case of human nature and behavior, however, almost all thinkers refused to extend any model of plant and animal behavior to human beings and, above all, to their essential behaviors of consciousness, knowledge, and choice. We had a soul. In the work of the French materialists, spiritualist explanations of any human behavior were deemed a dead end, simply an admission of ignorance. When we truly knew causes, we had natural, material explanations. When we did not know causes, we attributed them to God or spirits. As d’Holbach put it in works from 1770 onward, theology was nothing but “the ignorance of natural causes reduced to a system.”

In that sense, for the materialist atheists, spiritualism was a confession of helplessness and an abandonment of inquiry. Materialism alone removed the barriers to knowledge and mastery. It was an invitation to human exploration of the human phenomenon and a tearing down of boundaries to science. Indeed, they ultimately justified their materialism not on philosophical grounds but as a strategy of human knowledge, adaptation, interaction with nature, and survival.

We were not two beings, they argued, with the soul or mind distinct from the body. Rather, what we termed the soul was simply a behavior of the body. They noted the effect of illness, opiates, sexuality, the circulation of the blood, temperature, and age upon our cognitive and volitional capacities—something inexplicable, they argued, if soul and body were distinct but wholly comprehensible as a matter of physiology, including the physiology of the brain and nervous system. They insisted that human beings were not categorically distinct, and that the transition from other animals to man was gradual and founded upon observable physical differences of constitution, such as what was knowable from the evidence of comparative embryology and anatomy. The more complex the brain and central nervous system were, the more complex the cognitive and volitional capacity of any species. Animals, as any farmer or pet owner knew, they argued, engaged in ethical behaviors. What we named “soul” was the effect, not the cause, of the body’s behaviors, and nature had made us organisms who were capable of thought and capable of studying ourselves as a part of nature. In short, before such disciplines were even possible, they invited the creation of the sciences of physiological psychology, neuroscience, and comparative ethology. They invited the creation of a science of the human species without any limits set by theology or religion, indeed, without any limits set by anything but the desire for enhanced well-being and a reduction of suffering.


This desire for a wholly naturalistic science was most pronounced in the speculative (and posthumously published) works of Diderot. All matter—all nature—was potentially alive, moving between the “sensitive” and “insensitive” (what we would term the organic and the inorganic) by wholly natural and material agencies and catalysts, given time. Minerals became brain cells, and brain cells returned to being minerals. Physical forms and behaviors depended upon physical organization and catalysts. Life and death were two modes, two different organizations, of the same matter. For the French materialists, the hypothesis of God in science explained nothing, confused much, and was unnecessary.

In Le rêve de d’Alembert (D’Alembert’s Dream)—written in 1769, discussed among his friends, but unpublished until 1830—Diderot engaged in proto-evolutionary speculations, arguing that all species had emerged from prior forms in the course of periods of time almost immeasurably greater than that granted by Scripture, and, indeed, that all species would be ephemeral. The survival of a species, he and his friend Naigeon would write, depended upon its ability to “coexist” with an ever-changing nature. As d’Holbach urged in the Système de la nature (The System of Nature, 1770), mankind wished to see itself as the king of nature, but let one atom displace itself somewhere in the universe and it could set off a chain of determined events that would eliminate mankind from the universe entirely. Thus, our survival, for the atheistic materialists, depended upon successful adaptation to a changing natural environment, and that was the only and ultimate natural source of normative values. There was an ethic, then, to scientific truth itself: If we deluded ourselves, we betrayed not only our happiness but our lives. In his Additions aux pensées philosophiques (Additions to the Philosophical Thoughts, 1770), Diderot wrote about us as trying to find our way in a dark forest with only the small lantern of reason to guide us. Along comes a stranger, he wrote, who tells us that it is so dark that we should blow out the lantern. That man, Diderot concluded, is a theologian.

For d’Holbach, human life was a production of nature and wholly subject to its laws. Ignorant of those laws and desperate to preserve himself from pain and fear, man had invented illusory realities apart from nature, illusions on which he convinced himself that his well-being or suffering depended. This strategy, so to speak, had been profoundly dysfunctional for humankind. First, it had led us away from efforts to understand nature on its own real terms, which alone could put experience and knowledge in the service of the heart’s desire for ease from pain. We were forfeiting the very possibility of that happiness or diminution of suffering that we were seeking through religion and supernaturalism. Second, the turn away from nature, in addition to leaving us ignorant of real causes, had led us to create gods, superstitions, and myths as would-be routes to well-being, which, history taught us, had only increased our misery. Fearful and helpless, we turned to authorities that we believed could control the forces above nature, when it was our mastery of nature itself upon which our well-being depended. The only means of redressing the human condition was to see and study nature as the sole cause and site of all that concerned or affected us.

The foundation of morality, then, in this wholly naturalistic worldview, was the human desire for survival, pleasure, and social existence. The words virtue and vice, our moral language, only had meaning with reference to efforts to elicit behavior that served that desire and to suppress behavior that betrayed it. In Le rêve de d’Alembert, Diderot derived from this what he presented as the only two moral criteria: the useful and the pleasurable. If an act served both, as in procreation, with its pleasure and its benefit to society, all the better; but if something were useful without causing pain, or pleasurable without causing social harm, it was wholly moral. This elicited Diderot’s explicit philosophical defense of masturbation and homosexuality. All things were natural, and they were to be judged by the pain or pleasure they caused and by the harm or benefit to society and the species. Nature was in constant flux, and it could not be understood in terms of fixed essences. Homosexuality might be far less common than heterosexuality, but it was wholly as natural as that which was more frequent a phenomenon. It brought pleasure, and it caused no harm. That, for Diderot, settled the ethical argument.

In Le rêve de d’Alembert, Diderot suggested that the implications of atheism and naturalistic materialism for human beings were self-acceptance within the limits of possible change and self-improvement within the limits offered by knowledge of causes. Enlightenment atheism was unable to offer the explanations of spontaneous, that is, undesigned order that Charles Darwin could offer to unbelief. Rather, it turned its attention, above all else, to what it saw as the moral arguments and imperatives of understanding nature without recourse to a supreme being.


The particulars of the Enlightenment should not be understood in terms of the particulars of twenty-first century agendas. Rather, it bequeathed values, ways of thinking, and criteria whose potential would only be actualized by later phenomena and are being actualized still. Did Jefferson, for example, believe in the equality of races and of the sexes? No. He was deeply a man of his particular time and place. He urged, however, as “self-evident” that the then generic “man” was endowed with unalienable rights to “life, liberty, and the pursuit of happiness,” and that governments existed precisely to secure those preexistent rights. That is what Locke believed, and it is what most deists believed. The historical resonance of that belief, which Enlightenment thinkers proclaimed to be universal—whatever its authors thought to be its application in their lifetimes—has inspired virtually every movement for human legal equality and dignity. Did French Enlightenment authors—living in an age when more than four out of five of their countrymen were needed to work the land and most could not read a published book—believe in equal opportunity? No. They identified despotism as an ultimate horror, however, and embraced the view that society was a voluntary association of equal individuals. They rejected the presumptive authority of the past and invited posterity to work for a fairer, less cruel, and more humane future. They set loose in the world the secular values according to which all individuals should enhance their lives and reduce their suffering.

The seeds of a new way of viewing nature and our place in it and of proceeding toward human mastery of the natural causes of well-being or pain were now in the world. They announced a set of goals that changed the possibilities and, at times, the course of history: not only life, liberty, and the pursuit of happiness, but legal equality, a free science, a secular society within which religion is a matter of private and voluntary life, religious toleration, and a belief that government is the servant not the master of its citizens. The Enlightenment also bequeathed to us the freedom to disagree. In its wake, the debates of the modern age began in all of their intensity. For many of us, the Enlightenment also unloosed the great potential of natural humanity in the natural world.

Alan Charles Kors

Alan Charles Kors is one of the world’s leading scholars on the history of the Enlightenment. He served as editor in chief of the four-volume Encyclopedia of the Enlightenment (Oxford University Press, 2002) and was selected by the Teaching Company to teach an elegant course on The Birth of the Modern Mind.

The most influential contribution of the Enlightenment to modern thought, after its transformation of religious toleration from a negative to a positive value, was the secularization of ethical debate. Historically, however, it would be one-dimensional—indeed wrong—to understand this phenomenon as the product of a virgin birth of ideas in the Enlightenment. Both deistic and atheistic …

This article is available to subscribers only.
Subscribe now or log in to read this article.