Julien Offray de La Mettrie

Life and Works

Julien Offray de La Mettrie (1709–1751) was a French physician‑philosopher and one of the most outspoken materialists of the Enlightenment. Born in Saint-Malo into a bourgeois merchant family, he was initially educated by Jansenist teachers in Paris, then trained in medicine at Reims and Paris before further study under the prominent physician Hermann Boerhaave in Leiden. His medical background decisively shaped his philosophical outlook, especially his conviction that mental phenomena must be understood through physiology.

La Mettrie first gained attention not as a philosopher but as a medical writer and translator. In the 1730s and early 1740s he produced works on fever, venereal disease, and medical practice. His early philosophical orientation emerged in commentaries on Boerhaave, where he stressed the mechanistic functioning of the body and questioned traditional metaphysical appeals to an immaterial soul.

His reputation shifted dramatically with the publication of anti-religious and materialist texts that provoked strong condemnation from religious and political authorities. In Histoire naturelle de l’âme (1745, “Natural History of the Soul”), he argued that the soul’s operations were inseparable from bodily organization, effectively undermining the Cartesian dualist distinction between res cogitans (thinking substance) and res extensa (extended substance). Accused of impiety and materialism, he was forced to leave France for the Dutch Republic.

While in Leiden, La Mettrie composed his most famous work, L’Homme machine (1747, “Man a Machine”), anonymously published and rapidly banned. The book elaborated a comprehensive mechanistic and materialist theory of the human being, claiming that all mental life is rooted in the organization and movement of matter. Under pressure from Dutch authorities as well, La Mettrie again went into exile.

He found refuge at the court of Frederick II (Frederick the Great) in Berlin. Frederick, who admired French culture and tolerated unorthodox ideas, appointed him court reader and physician. In Berlin, La Mettrie continued to write prolifically, turning from strictly physiological issues to broader ethical and political themes. Important works from this period include L’Art de jouir (The Art of Enjoyment), Discours sur le bonheur (Discourse on Happiness), and Anti-Sénèque (Anti-Seneca), in which he developed a controversial defense of hedonism and challenged Stoic and Christian moral ideals.

La Mettrie died in Berlin in 1751, reportedly after an illness triggered by overindulgence at a banquet given in his honor by the French ambassador—circumstances his critics treated as emblematic of the excesses of his philosophy, and which his defenders viewed as anecdotal or exaggerated. Frederick the Great arranged for his burial and later wrote a brief but respectful biographical sketch.

Philosophical Thought

La Mettrie’s philosophy centers on a radical materialism applied to the mind, ethics, and religion. Combining medical observation with mechanistic physics, he argued that human beings are entirely corporeal, self-moving machines whose thoughts and feelings arise from the complex organization of their bodies.

In L’Homme machine, he extends and radicalizes the Cartesian machine analogy. Descartes had compared animals to machines but reserved an immaterial soul for human rationality. La Mettrie rejects this asymmetry: for him, animals and humans form a continuum, differing in degree of complexity rather than in kind. He points to anatomical similarities, gradations in cognitive ability, and the effects of injury, disease, and intoxication on mental states as empirical evidence that consciousness is inseparable from bodily conditions. The brain, nervous system, and circulation are treated as the physical basis of thought, memory, and emotion.

This view directly challenges dualism and traditional theological doctrines. La Mettrie denies the need for a separate spiritual substance to account for mental life; instead, he maintains that matter itself can think when arranged in sufficiently complex ways. Proponents regard this as an early anticipation of later materialist theories of mind and, in a broad sense, of naturalistic approaches in neuroscience and cognitive science. Critics at the time saw it as a reductive position that failed to account for the apparent autonomy and normativity of reason, or for moral and religious experience.

La Mettrie’s epistemology is closely tied to empiricism. He emphasizes sensation and experience as the foundations of knowledge and expresses skepticism about purely speculative metaphysics. Human understanding is limited by our bodily senses and the structure of our organs. Nonetheless, he places great confidence in the progress of experimental science, especially physiology, to explain psychological and moral phenomena previously attributed to the soul.

In ethics, La Mettrie advances a bold form of hedonism. In texts like Discours sur le bonheur and Anti-Sénèque, he argues that the pursuit of pleasure and the avoidance of pain are natural and legitimate human goals. He attacks Stoic and Christian valorization of self-denial, suffering, and asceticism as contrary to human nature. Happiness, he claims, is found in the harmonious satisfaction of bodily and psychological needs, moderated by prudence and social considerations.

Critics contend that La Mettrie’s hedonism risks justifying egoism and undermining stable moral norms, a worry shared even by some of his Enlightenment contemporaries, who preferred more moderate or socially grounded conceptions of happiness. Supporters, by contrast, see in his writings an attempt to naturalize ethics, making moral life continuous with human physiology, psychology, and sociality rather than dependent on supernatural command.

La Mettrie’s religious views are often described as atheistic or at least strongly antitheological. He attacks doctrines of an immortal soul and divine providence as unsupported by evidence and as sources of fear and repression. However, he sometimes tempers his position with pragmatic considerations, acknowledging that religious beliefs may function socially for some people. Overall, his thought contributes to the radical wing of Enlightenment freethought, where criticisms of religion are linked to broader defenses of bodily autonomy and secular morality.

Reception and Legacy

La Mettrie’s works were widely condemned in his own time. Religious authorities denounced them as materialist, immoral, and impious, and even many philosophes within the French Enlightenment found his explicit hedonism and open rejection of spiritual substance politically dangerous. Figures such as Denis Diderot and Baron d’Holbach—who themselves advocated forms of materialism—sometimes treated La Mettrie as a useful but extreme example, distancing their own positions from his unapologetic celebration of sensual pleasure.

Nonetheless, La Mettrie’s writings circulated clandestinely and influenced the clandestine philosophical literature of the 18th century. His emphasis on the continuity between humans and animals, and on the dependence of mental life on the nervous system, resonated with later developments in physiology, psychology, and anthropology. Some historians of philosophy regard him as a precursor of scientific naturalism and of later debates about reductionism in the philosophy of mind.

In the 19th and 20th centuries, La Mettrie’s work attracted periodic renewed interest. Materialist and positivist thinkers sometimes cited him as an early ally in the effort to explain mind and morality without recourse to spirit or God. At the same time, critics in idealist and religious traditions pointed to him as an example of what they saw as the limits of mechanistic explanations of human life.

Contemporary scholarship often situates La Mettrie as a key but marginal figure in the Enlightenment: less institutionally central than Voltaire or Rousseau, yet crucial for understanding the radical edge of Enlightenment thought. Studies emphasize the integration in his work of medical practice, physiology, and philosophy, and explore how his materialism helped open questions that continue to shape discussions in philosophy of mind, bioethics, and secular ethics.

La Mettrie’s legacy thus lies not in a systematic philosophical school bearing his name, but in his role as a provocative catalyst. His insistence that humans are thinking machines, and that happiness is rooted in the embodied conditions of life, continues to inform historical debates about the Enlightenment and ongoing controversies over the scope and limits of a purely naturalistic understanding of human beings.