Francesca di Poppa. New Dictionary of the History of Ideas. Editor: Maryanne Cline Horowitz. Volume 4. Detroit: Charles Scribner’s Sons, 2005.
Materialism is the generic name of a variety of doctrines that deny the existence of non-material substances. Materialism may be either a metaphysical or a methodological concept. In its most coherent and radical form, it is a type of monism, the metaphysical position stating that there is only one principle—matter and its properties—in terms of which all reality is to be explained.
In the eighteenth century, materialism developed into a philosophy and gained a following that continues into the present day. Some eighteenth-century materialist philosophers were downright atheists. A few philosophers, such as the Stoics or Thomas Hobbes, while not atheists, held that God is corporeal. Others preferred some form of deism, the idea that a transcendent, noninterventionist God rules the world through constitutive laws of nature. For them, materialism was a methodology to follow when inquiring about the natural world, rather than a complete metaphysical commitment.
Materialism should not simply be identified with the Enlightenment, the eighteenth-century cultural movement that endorsed an understanding of the natural world, including humankind, based exclusively on reason, with no possibility of appeal to the supernatural. The Enlightenment included a secular interpretation of ethics and politics. While materialistic trends were an important part of the Enlightenment, its scope and philosophical commitments were far broader and more varied, involving an agenda that was political as well as philosophical including, in the case of several important thinkers, a straightforward belief in a God who acts in the world.
Eighteenth-century materialism in a sense is an extension of the seventeenth-century mechanical philosophy that was the hallmark of the scientific revolution. The mechanical philosophy offered a worldview in which matter and the natural laws of motions were supposed to explain all phenomena. In the seventeenth century, only Thomas Hobbes (1588-1679), in Leviathan (1651) and other works, and (in a much more problematic way) Baruch Spinoza (1632-1677) went so far as to argue that the mechanical philosophy could explain all the aspects of mental life. Later in the century, such monistic views, as well as trends that were inherent in the philosophy of René Descartes (1596-1650), such as the reduction of nonhuman forms of life to automata, developed the form of materialism that was characteristic of the eighteenth century.
Despite the coherence of Hobbes’s materialism, the authors who were most fundamental to the passage from seventeenth-century mechanical philosophy to eighteenth-century materialism were Isaac Newton (1642-1727) and John Locke (1632-1704). Isaac Newton was a multifaceted, iconoclastic figure. He can hardly be called a materialist in any metaphysical sense. However, the impressive results he achieved in physics gave an impulse to methodological materialism in science and well beyond. John Locke’s Essay concerning Human Understanding (1690; 4th edition published in 1700) developed a sensationalist psychology, based on the idea that sense perception and mental mechanisms of reason, usually in the form of calculation and association, explain all mental life without the need to postulate any nonmaterial substance. Locke famously debated whether material things (such as rocks) could think. He concluded that God could have created thinking matter and was opposed by Bishop Edward Stillingfleet (1635-1699). Locke’s position was later then taken up by Anthony Collins (1676-1729) against Samuel Clarke (1675-1729). A follower of Newton, Clarke is well known because of his controversy with Gottfried Wilhelm von Leibniz (1646-1716).
Another relevant source of ideas came from the French-based seventeenth-century movement of the libertines, or freethinkers (not meant as a compliment), who opposed religious oppression, and who, often in anonymous publications, defended the free use of reason against the suffocating Catholic Counter-Reformation. Libertines challenged religious authority in morals and politics, using ideas inspired mainly by the materialism of the ancient atomistic, Epicurean, and skeptical traditions. To this movement belong authors as different as Pierre Gassendi (1592-1655) and Cyrano de Bergerac (1619-1655). The anonymous Theophrastus redivivus, published around 1660, espoused the most radical theses of libertinism, such as atheism, materialism, and a form of ethical Epicurean hedonism.
The Eighteenth Century
The eighteenth century was an age of prodigious scientific learning. While the seventeenth century’s philosophical milieu was influenced mainly by physics (mechanics and cosmology), the eighteenth century became especially fascinated with chemistry, or the constitution of matter, and by the phenomenon of life and its forms of organization. In this sense, materialist philosophers and scientists were strongly motivated to explain the complexities and diversities of life without reference to divine intervention.
The diversity of life had been unprecedentedly systematized by Carolus Linnaeus (1707-1778), whose Systema naturae (System of nature) was published in 1735; however, biological diversity was well known long before the eighteenth century, and the discoveries explorers made around the world drew the attention of many scientists. The ideas of evolution and adaptation had begun to gain momentum, championed in different forms by Buffon and by Diderot. Between the end of the eighteenth century and the beginning of the nineteenth, evolution of species was a concept that, though rejected by most, was part of the scientific debate with the works of Jean-Baptiste Lamarck (1744-1829) and Erasmus Darwin (1731-1802). They both struggled with an account of life and diversity based on adaptation to a changing environment and competition for resources.
Another major scientific figure was Antoine-Laurent Lavoisier (1743-1794). Known as the scientist who began the chemical revolution by changing the concept of chemical element and discovering oxygen, which term he coined, Lavoisier developed a new physicochemical nomenclature that stressed the quantitative aspects of combining chemical elements. While Lavoisier was not particularly philosophical, his revisions of the structure of chemical knowledge, and thus of matter theory, brought about a change in the understanding of matter and the mechanisms by which it worked. In this sense, Lavoisier was like many other scientists in the eighteenth century: while maybe not metaphysical materialists themselves, they helped develop a scientific methodological materialism that could support a metaphysical alternative to religion and traditional dualism. Lavoisier, who was a tax collector for the royal government, was guillotined in 1794 during the French Revolution.
François Marie Arouet, better known as Voltaire (1694-1778), endorsed Locke’s sensationalism and argued against Spinoza and Nicolas Malebranche (1638-1715) in his Dictionnaire philosophique (1764; Philosophical dictionary) and Lettres anglaises ou philosophiques (1734; English or philosophical letters). He also became very popular as an apologist for Newton, with his Éléments de la philosophie de Newton (1738; Elements of Newton’s philosphy). Voltaire opposed institutionalized religion and intolerance based on superstition, and, although not an atheist, he supported the rationalistic deism. His famous Candide (1759) is a witty and ironic, though simplistic, lampoon of Leibniz’s metaphysics of the best of all possible worlds.
His mistress and patron of the great French salon, Madame Émilie du Châtelet, who, with his aid, translated Newton’s Principia mathematica into French, was also a prominent supporter of Newtonianism and did much to publicize these new scientific views. They were both forced to flee Paris in 1747. Once in Berlin, Voltaire entered a dispute with his old friend and protégé Pierre-Louis Moreau de Maupertuis (1698-1759), the president of the Berlin Academy and author ofVenus physique (1745; The physical Venus) and Système de la nature (1751; System of nature).
Paul-Henri-Dietrich d’Holbach’s (1723-1789) most famous book, Système de la nature, ou des loix du monde physique et du monde moral (1770; The system of nature, or the laws of the physical and moral world), was published under the name of J. B. Mirabaud. Following the tenets of Epicurean atomism, the book derided religion and espoused an atheistic, deterministic materialism: all causation was reduced to patterns of motion, man became a machine devoid of free will, and religion was excoriated as not just untrue, but dangerous. Système social (1773; Social system) placed morality and politics in a utilitarian framework: duty was reduced to prudent self-interest. D’Holbach used his inherited fortune to support Diderot’s Encyclopédie project, writing many articles for these volumes himself and translating from German.
George Louis Leclerc, comte de Buffon (1707-1788) was appointed to the French Academy of Science in 1734; in 1739 he became superintendent of the Royal Botanical Garden (Jardin du Roi; present-day Jardin des Plantes). Buffon was given the task of completing a catalog of the royal collections in natural history, which he transformed into a project to produce an account of the whole of nature. This became his great work, Histoire naturelle, générale et particulière (1749-1804; General and particular natural history), which was the first modern attempt to systematically present all existing knowledge in the fields of natural history, geology, and anthropology in a single publication. Buffon criticized the Swedish naturalist Linnaeus for the artificiality of his taxonomy of plants and animals. Buffon opposed metaphysics in science, denied divine intervention in nature, and was Newtonian in believing that knowledge should be derived from observations of natural phenomena. He held that what separated humans from animals was reason alone, through their use of language. He was the first to reconstruct a geological history, including a discussion of nature and a theory of the age of the earth, in a series of stages in Histoire et théorie de la terre (1749; History and theory of the Earth), and in Époques de la nature (1778; Epochs of nature), he proposed the theory that the planets had been created in a collision between the sun and a comet. His theory of the age of the Earth incensed religious opponents. Buffon divided matter into vital and nonvital, balancing an overall Newtonian physical framework with vitalistic tendencies (though rejecting nonmaterial substances). So, he opposed the idea that life was a form of organization of matter. On the other hand, life being a property of matter (of “organic molecules”), it does not require any explanatory principle external to matter. Buffon believed in spontaneous generation as resulting from aggregation of organic molecules present in the environment; his theory was criticized by Lazzaro Spallanzani (1729-1799), whose experiments confirmed Francesco Redi’s (1626-1697) rejection of spontaneous generation.
The outcry following publication of Julien Offroy de La Mettrie’s (1709-1751) materialistic views in Histoire naturelle de l’âme (1745; Natural history of the soul) forced his departure from Paris. In Holland, in 1747, he published L’homme machine (The man-machine), which was publicly burned, even in that notoriously liberal environment. La Mettrie then fled to Berlin to ask for the protection of Frederick II of Prussia (r. 1740-1786). La Mettrie, in opposition to Descartes, held that matter was not only extended, but also endowed with an inherent principle of motion and that it could have sensations. Humans were infinitely more complex than lower machines, yet they were still machines. La Mettrie suggested that atheism and an ethics of hedonism were the only proper paths toward human happiness.
Claude Adrien Helvétius (1715-1771) in his De l’esprit (1758; On the spirit) explains all of human reason as being based on sensation (like Locke and Condillac). Like La Mettrie, Helvétius placed humans on a continuum with animals. Helvétius also adumbrated a somewhat Epicurean ethical system based on self-interest, pleasure, and pain. His book provoked an outraged reaction both in the court and in the schools; both the Sorbonne and the Parlement of Paris condemned it. Despite Helvétius’s public recantation, it was burned publicly (along with the works of other philosophes like Voltaire). Helvétius, like La Mettrie, was welcomed at the Prussian court in Berlin.
Étienne Bonnot de Condillac (1715-1780) maintained an empirical sensationalism based on the principle that observations made by sense perception are the foundation for all human knowledge. The ideas of his L’essai sur l’origine des connaissances humaines (1746; Essay on the origins of human knowledge) are close to Locke’s, though on certain points, as in rejecting what he took to be Locke’s innate ideas of reflection, Condillac modified Locke’s position. In his most significant work, the Traité des sensations (1754; Treatise on sensations), Condillac denied, for example, that the human mind makes inferences about the shapes, sizes, positions, and distances of objects. Examining each sense separately and the knowledge thereby obtained, he concluded that all human knowledge is sensation transformed by language. Modeled on algebra, language was the underlying principle used to form all higher cognition. In this work he famously analogized man to a statue who gains complex reasoning from its underlying sensations. The importance of language to thought and rational progress is one of the major themes of the Enlightenment. Despite Condillac’s materialistic psychology, he believed his views about the nature of religion, especially the reality of the soul, to be consistent with his sensationalism. Condillac’s own brand of sensationalism had many followers in Italy. In particular, the jurists Giandomenico Romagnosi (1761-1835), Cesare Beccaria (1738-1794), and Melchiorre Gioia (1767-1829) used his epistemology as a basis for a rationalistic study of jurisprudence and political and social theory.
In 1745 the publisher André Le Breton (1708-1779) approached Denis Diderot (1713-1784) with a proposal to produce a French translation of Ephraim Chambers’s Cyclopaedia, (first edition, 1728). Together with the mathematician and philosopher Jean Le Rond d’Alembert, Diderot transformed the project into the great Encyclopédie. By adhering to strictly rationalistic and materialistic principles, Diderot and d’Alembert saw themselves as forging a weapon against the hold of religion on science and human knowledge. In 1749, Diderot published the Lettre sur les aveugles à la usage de ceux qui voient (An essay on the blind for those who can see), remarkable for introducing the first sketch of Diderot’s “evolutionary theory” of survival by adaptation. The existence of diversity and monstrosities in nature is explained by a theory of evolution from chaos; the apparent order and adaptation is explained with a probabilistic argument, since nature has time for innumerable trials that lead to growth, increased complexity, and specialization. Only the organisms that became adapted to their environment could survive. Diderot held that our sensory organs, not ideas about essences, should determine our metaphysics. This open endorsement of radical materialism was condemned and, in 1749, led to Diderot’s being incarcerated for three months.
Another ugly moment for Diderot came when Helvétius’s De l’esprit, was condemned to be burned by the Parlement of Paris in 1758, and the Encyclopédie itself was formally suppressed. Diderot published the remaining volumes semiclandestinely. Among his philosophical works, special mention may be made of L’entretien entre d’Alembert et Diderot (written 1769, published 1830; Conversation between d’Alembert and Diderot), Le rêve de d’Alembert (written 1769, published 1830; D’Alembert’s dream), and the Éléments de physiologie (1774-1780; Elements of physiology). In these works Diderot developed his materialist philosophy and concluded that simple, reductive mechanical explanations are not sufficient to explain sentient life, without assuming that all matter is potentially sentient and that life and sentiency are specialized functions that arise from a higher level of complexity. In Jacques le fataliste (1771; Jacques, the fatalist) Diderot gave a common sense solution of the problem of free will: while there are no rational arguments to support free will, he argued that extreme determinism is ultimately self-defeating.
Jean Le Rond d’Alembert (1717-1783) attended a prestigious Jansenist school where he developed a lifelong distaste for religion. After studying law for two years and medicine for one, he finally discovered his passion for mathematics, which he mainly taught himself. In 1739 he read his first paper to the French Academy of Sciences, of which he became a member in 1741. In 1743 he published his Traité de dynamique (A treatise on dynamics), containing the famous “d’Alembert’s principle,” stating that Newton’s third law of motion (for every action there is an equal and opposite reaction) is true for both freely moving and fixed bodies. Other mathematical works followed; in particular the development of partial differential equations. In 1745, d’Alembert joined Diderot in the Encyclopédie project as editor of the mathematical and scientific sections. In fact, his contribution went much further, including the Discours préliminaire (Preliminary discourse) that introduced the first volume in 1751. The introduction endorsed a view of science as a unified and rational enterprise.
Besides the authors mentioned above, it is useful to recall that there was a clandestine literature that offered materialistic responses to Descartes and that most likely contributed to the philosophical educations of the authors listed. Of particular interest, a collection of manuscripts at the Douai library (ms. 702), on which appears the date 1723, and contains, among others, a Dissertation sur le sentiment des bêtes, l’instinct et la raison, contre les Cartésiens(Essay on the feelings of animals, instincts and reasons, against Cartesians); L’essai philosophique sur l’âme des bêtes(Amsterdam, 1732; Philosophical essay on the soul of animals); and Principes physiques de la raison et des passions des hommes (1709; Physical principles of reason and passions of men) by a Dr. Maubec. Most of this literature, while it circulated widely in its day, is still available only in manuscript.
A late-eighteenth-century figure, Pierre-Jean-Georges Cabanis (1757-1808), was a French philosopher, physician, and physiologist who published Rapports du physique et du moral de l’homme (1802; Relations of the physical and moral of man). Cabanis, opposing Condillac’s sensationalism, explained all of reality, including the mind-body relations in man, in terms of a mechanistic materialism built on the organic needs of an organism and its automatic responses (the irritable properties of tissues). For Cabanis, life was merely an organization of physical forces; “secretions” in the brain, analogous to the liver’s secretion of bile, produced thoughts. The concept of soul was superfluous, since consciousness was merely an effect of mechanistic processes, and sensibility, the source of intelligence, was a property of the nervous system. Cabanis is best known, however, as a medical reformer who brought new ways of health care and medical education to France.
John Toland (1670-1722) was born Catholic, though he converted to Protestantism and later endorsed Socinianism, which, like Unitarianism, denied the doctrine of the Trinity. He wrote several texts in which he supported a naturalized and historical interpretation of the holy texts and of miracles. In Christianity not Mysterious (1696) he claimed that reason is sufficient to explain all religious “mysteries.” In Letters to Serena (1704) and Pantheisticon (1720), he endorsed a form of pantheism in which God-soul is identical with the material universe. He defended Giordano Bruno (1548-1600), whose pantheistic and materialistic philosophy obviously influenced him. Pantheism was the doctrine that God was everywhere and was all things.
Anthony Collins (1676-1729) was a provocative author who argued, in his Discourse of Free-thinking (1713, published anonymously), that free and rational inquiry is the best defense for religion against atheism. In Inquiry concerning Human Liberty and Necessity (1715) and Liberty and Necessity (1729), he denied free will and defended determinism on the grounds of the necessity of a cause-and-effect relationship between events. He wrote A Letter to Mr. Dodwell (1707), to which Samuel Clarke, Newton’s disciple, responded. This led to a two-year correspondence (1706-1708) in which Toland defended the idea that all life and consciousness arises from emergent properties of systems of material particles.
David Hartley (1705-1757) saw himself as carrying out Newton’s scientific project for the human being and offered a physiological explanation for the association of ideas in materialistic terms in his Observations on Man: His Frame, His Duty, and His Expectations (1749). Hartley used Newton’s theory of vibrating corpuscular matter and forces of attraction and repulsion as a metaphysical basis for Locke’s associationist psychology. He explained mental life in terms of associations and inhibitions, which themselves were to be explained by attraction and repulsion in the nervous system and the brain. Hartley, however, was a deeply religious thinker who believed that “theopathy,” the love of God, was a natural emotion, and whose depiction of salvation bordered on mysticism.
Joseph Priestley (1733-1804) was a freethinker who formally rejected Calvinism to enter the Unitarian denomination. Priestley is known mainly for his work in physics and chemistry. He consistently pursued science as a rational enterprise based on facts and experimentation, rather than on dogmatic principles. His view of nature was informed by his belief in a benevolent God who operates through laws of nature that become accessible through careful observation. While this belief in God somehow influenced Priestley’s heuristics, his work in chemistry and physics and his political and economic theories were informed by a methodological materialism in which only matter and natural laws were relevant. Between 1772 and 1790, he published six volumes of Experiments and Observations on Different Kinds of Air and several papers in the Philosophical Transactions of the Royal Society, of which he was a member. He is well known for his contributions to the chemistry of gases, and for his development of a theory of phlogisticated air (which was opposed to Lavoisier’s, who repeated Priestley’s experiments, and rejected the phlogiston theory in favor of his new oxygen theory).
While it is difficult to find philosophically important individual (materialist) thinkers in other European countries, the materialistic current of the Enlightenment and its belief in the virtues of science swept through Europe, influencing, more or less directly, the political life in every country, with the endorsement of various forms of scientific progress and “enlightened” government. The application of science and the scientific method, mostly based on methodological materialist doctrines, became the hallmark of progress (itself an early-eighteenth-century notion). These beliefs brought important changes in urban development, public health, and industry thoughout Europe.
The influence of European political and social thought, especially concerning tolerance and education, was also felt by American writers and had a fundamental role in the American Revolution and the writing of the U.S. Constitution. However, no movement endorsing materialism, methodological or metaphysical, can be traced.