Alan M. Levine, American University
Darren M. Staloff, City College of New York and City University of New York

The theory of natural law was a vital part of the Enlightenment as evidenced by the writings of Grotius, Locke, and Pufendorf in the seventeenth century and Vattel and Burlamaqui in the eighteenth. Revealed by reason, natural law was for these thinkers a universal pre-political standard for human action, morally constraining on individuals and regimes alike.

Several other Enlightenment thinkers, however, reconceived and eventually eliminated natural law as a prescriptive guide for human action due to a variety of moral, political, and epistemological doubts. Some thinkers were suspicious of the traditional accounts of natural law (upon which European religious, moral, and political thought had largely depended up to that time) because of their perceived susceptibility to abuse. Natural law’s claims to certainty were undermined by the perceived corruption within the Catholic Church and the dogmatic, sectarian, and murderous religious strife of the sixteenth and seventeenth centuries. More broadly, the discovery of the New World shook the foundations of Christian cosmology, the recovery of ancient texts (due to increased trade with the Muslim world and the fall of Constantinople) revealed healthy and happy people despite—or because of—the absence of Christianity, and the rise of science led many thinkers to view the traditional natural-law perspective as parochial and insufficient. Natural law theory’s appeal to cosmological patterns of universality was similarly taken to be incompatible with the humanism that had come to inform much of Western thought since the Renaissance. Natural law’s universality was seen to be not only anthropologically simplistic but also a dangerous bulwark of the intolerance that underlay the preceding era of religious and political persecution. Moreover, as the older conception of reason as a faculty of the soul capable of objectively knowing the world gave way to the Lockean view of reason as a purely calculative operation of the mind, doubt arose as to whether any such universal, rationally knowable moral principles could exist. The “inductive” logic associated with the scientific revolution suggested that moral knowledge was more likely to come from an analysis of the empirical facts of moral belief that would accurately describe or explain behavior than from an a priori system of prescriptive ethical or political teachings.

Given these doubts, Enlightenment critics sought to replace traditional natural law theory with more worldly sources of moral and political knowledge. These critics can be classified under three categories: the “naturalizers,” the moral reductionists, and the most radical theorists who proposed entirely new moral theories that were every bit as prescriptive as traditional natural law theory.

Naturalizing Natural Law

Naturalizers such as Voltaire, Diderot, and their precursors (such as Montaigne) continued to use the vocabulary of natural law, but redefined what natural law is and how it can be known in terms of a new conception of the natural. Unlike natural law theory’s ancient pagan and Christian adherents, they argued that natural law cannot be rationally deduced from claims of a natural human end (telos) or from biblical accounts of God or Eden (which they deemed to be unprovable or unknowable). Instead, they tried to deduce laws of nature from hypothetical accounts of humankind in its original state, accounts that were purportedly grounded in anthropological observation. According to this view, natural law was not a moral command of reason, but rather a set of maxims drawn from the empirical facts of the natural human condition.

The contractarians Hobbes, Locke, and Rousseau talked in terms of a “state of nature,” while Montaigne and Voltaire argued from their observations of Native Americans as Diderot did with his Tahitians. Despite their varied approaches, all of the naturalizers adhered to a similar “primitivism,” taking the natural, “pure” standard of human behavior to be its pre-civilized state. The nature that they found tended to lead them away from the existing realities of Europe and toward liberal political institutions. These thinkers judged Europe’s (and indeed all) religious, political, social, and economic institutions in light of their theoretical accounts of truly natural man. In the late Enlightenment they particularly attacked religious institutions, especially the Catholic Church, for their corruption and deviance from nature (and, as a rhetorical point, from the words of Christ). They critiqued monarchy, aristocracy, and other forms of hereditary inequality, lamenting the artificial, unfair class system and social norms based on pomp and pretension. They aimed to restore psychological wholeness, inner tranquility, and happiness to the conflicted, unhappy, and unhealthy people suffering under institutions justified by traditional interpretations of natural law. In addition, attracted by the cheerful embrace of pleasure in “noble savagery,” they called for the acceptance of simple, innocent pleasures as well as refined hedonism.

Moral Reductionism

The second main way in which Enlightenment thinkers challenged natural law was by rejecting its prescriptive function entirely and offering instead a reductive account of morality grounded in the extra-rational facts of human psychology. Unlike natural law, such reductivism could not issue normative commands from on high. It could, however, clarify moral and political principles and purposes and show how their application might be maximized. These thinkers were thus able to engage in social criticism, albeit not as much as the naturalizers, by showing how existing social or political practices violated those principles and purposes. This strategy had two distinct strains.

One strain of reductionism, sometimes called modern Epicureanism, based its moral code on self-love or amour-propre. Drawing on the worldly musings of Saint Evremonde and La Rochefoucauld, thinkers like Voltaire and Mandeville insisted that moral judgment was grounded in the universal desire for happiness and pleasure, and that the public good was the socially useful, just as the private good was whatever resulted in individual happiness. Unlike natural law theory, such a moral science was relativistic: it argued that the measures and forms of government, law, and morality most likely to result in happiness varied by custom, convention, and mores. Thus its implications could be quite radical. Insofar as religious institutions and practices occluded happiness and led to suffering  (as in the Calas affair)[1] a figure like Voltaire felt fully justified in trying to écraser l’infâme (“crush the vile thing”). Similarly for Mandeville, an awareness of the importance of wealth, power, and commercial prosperity for the happiness of a nation led him to insist that private vices were in fact public benefits if prudently regulated.

The second strain of reductionism, prevalent particularly within the Scottish Enlightenment, claimed the imprimatur of science, specifically a modern “science of human nature,” and traced the origins of normative judgment to affective psychology rather than to rational self-interest. Shaftesbury was the first to treat ethical knowledge as more like the cultivation of an innate moral sense than rational demonstration. This notion was then picked up and amplified by Hutcheson, Hume, and Smith, all of whom described morality as issuing from the “cool” passions of benevolence and an instinctive sympathy for our fellow creatures. Like the Epicureans, they thought that political wisdom and moral truth served to maximize human happiness and public utility, but they insisted that rational thought played little if any part in actual moral judgment. Instead, these would-be moral scientists argued that morality issued more from the heart than the head. Even the norms associated with traditional natural law were, in this account, the result of human sociability and fellow feeling as applied to particular contexts, and hence were only salutary fictions. Nor were they always salutary, as Edmund Burke observed in the context of the French Revolution. Also like the Epicureans, the devotees of moral sense avoided the presumed dogmatism of the natural law tradition by embracing a certain degree of relativism in cultural, moral, and political arrangements.

Prescriptive Replacements of Natural Law

Toward the end of the Enlightenment, there emerged a more radical alternative to natural law. Like reductionism, it denied natural law any validity at all and replaced it with a fresh source of moral and political authority. Unlike the reductionists, however, the proponents of this strategy sought to maintain the prescriptive power traditionally associated with natural law.

There were three notable attempts of this kind. Jean-Jacques Rousseau offered the best known, most radical, and most influential one, which embraced the “general will” as the infallible and universal source of any legitimate authority. Like natural law, the general will was rationally knowable and binding, but it was also rooted in what, for Rousseau at least, were thought to be the empirically given realities of each political association. This doctrine was therefore significantly variable from polity to polity yet thought to be both certain and scientifically respectable, descriptive and prescriptive. Not surprisingly it proved a potent weapon in the rhetorical arsenal of the French Revolution. Like Rousseau, the Physiocrats Mirabeau and Quesnay sought an ultimate source of normative judgment that was both descriptive and prescriptive. In their case, however, that source was pre-civilized nature, which privileged agriculture as the solely productive sector in political economy. Physiocracy was not a revolutionary creed like the “general will” (most of its followers ascribed to the doctrine of “legal despotism”), but it did lead to a demonstrably liberal, laissez-faire model of economic policy in order to maximize agricultural productivity. Still others combined the core insights of Physiocratic political economy with the empirical facts of human sensibility. Known as sensationists or “Ideologues,” these thinkers were largely disciples of Condillac, such as Helvetius, Condorcet, Cabanis, Tracy and others. Their metaphysical analysis—so unique among Enlightenment critics of natural law—and their materialist reading of human sensibility entailed that mankind necessarily sought to avoid pain and fulfill its desires and wills. Given the universality of this fact, they claimed to demonstrate that a broadly republican and liberal political order was the sole way to achieve these goals. Like natural law, each of these “replacements” could be used to legitimate and/or criticize government policy and moral judgment. Each also claimed the same certainty and universality of natural law, but all three sought to ground the source of normative truth in “fact,” a strategy that would culminate in Comtean positivism.


The Enlightenment’s rejection of natural law had profound implications for both political theory and practice in the eighteenth century. Non-prescriptive reductionism marked the most radical intellectual departure from the preceding tradition of moral and political thought. Because it took every individual and culture to be inherently morally upright, it left to the philosopher only the limited “scientific” task of inductively demonstrating how moral norms arose. Naturalizers, by contrast, were less philosophically radical. They jettisoned natural law theory’s traditional moorings, but they retained its language and the movement of its thought, making prescriptive claims, but in a piecemeal, non-comprehensive manner. The least philosophically radical strategy was that of offering prescriptive replacements for natural law. The prescriptions were new, but they functioned largely in the same fashion as what they replaced, offering mandatory and certain guides to moral and political action: one set of a priori principles was simply replaced with another.

From the perspective of political practice, however, the respective implications of each of these philosophies were almost entirely the reverse. Prescriptive replacements for natural law offered a revolutionary political agenda whose universality and certainty underwrote and legitimated the radical and often violent measures required to put them into effect. French revolutionary thought drew heavily on Rousseau, Physiocracy, and the ideas of early Ideologues, such as Condorcet and Sieyes. Naturalizers like Voltaire and Diderot were comparatively mild in their political prescriptions, offering grounds for criticism and reform but not wholesale reconstruction. The anthropological primitivism of the “noble savage” highlighted certain failures of the European moral and political order, but none of its adherents seriously believed that contemporary societies could or should return to that more primitive state. By contrast, in a purely political sense, the reductionists were the least radical. Since they viewed moral and political norms as given natural phenomena, their moral theories offered little ground for political reconstruction. In fact, this strategy aimed to lower the stakes of and polemics surrounding political action and debate by showing that there were few moral problems to solve. It sought to convince the literate public that the contemporary world was already imbued with all the moral and political norms it needed, and thus required little intervention. If anything, its purpose was to make contemporary Europeans satisfied with the modern social and political order emerging in their midst.


[1] A Protestant living in Catholic France, Jean Calas was accused of murdering his son for religious motives (several years earlier, another of Calas’ sons had converted to Catholicism, and it was rumored that this son was planning to as well). Calas claimed his innocence to his death by torture on the wheel in 1762. His death garnered the interest of Voltaire, who eventually had his conviction overturned on the grounds that Calas had been unjustly convicted out of anti-Protestant prejudice.