Charles Bonnet

Life and Scientific Work

Charles Bonnet (1720–1793) was born in Geneva into a prosperous and educated family of the French‑speaking Protestant bourgeoisie. Trained initially in law at his family’s insistence, he devoted his energy from an early age to natural history, especially entomology and plant physiology. His first major work, Traité d’insectologie (1745), based in part on meticulous observations of aphids, established him as a respected figure among European naturalists.

In his early research, Bonnet contributed empirical support to preformationism, the view that organisms develop from miniature, pre‑formed entities (often called “germ” or “embryo”) rather than from undifferentiated matter. His observations of parthenogenesis in aphids (reproduction without fertilisation) seemed to him to confirm the existence of pre‑existing germs already containing the structure of future organisms. These findings were influential in the 18th‑century debates over generation, even as later biology would move toward epigenetic models of development.

A turning point in Bonnet’s life came when progressive vision loss forced him to restrict direct observation. From the 1750s onwards he gradually turned from hands‑on natural history to more speculative reflection on the philosophical implications of physiology and psychology. Although nearly blind in his later years, he continued to write and dictate substantial works.

Bonnet’s major philosophical and scientific syntheses include Essai de psychologie (1755) and Essai analytique sur les facultés de l’âme (1760), in which he integrated experimental psychology, natural history, and metaphysical speculation. In La palingénésie philosophique (1769), he developed an elaborate theory of the “great chain of being”, imagining the universe as filled with hierarchically ordered beings undergoing cycles of improvement and rebirth, in line with a broadly theistic and optimistic view of nature.

Bonnet spent most of his life in and around Geneva, an independent republic at the time, and interacted with intellectuals across Europe, including members of the French Enlightenment. While he shared many of their interests, he remained religiously conservative, aiming to reconcile natural history with Protestant theology rather than to undermine traditional belief.

Philosophical Views and Theories of Mind

Bonnet’s philosophical work centres on the relationship between mind and body and the mechanisms of perception and cognition. Influenced by empiricism (especially Locke and the French sensationists), he nonetheless maintained a dualist framework in which the soul is distinct from the body but constantly correlated with it.

A key doctrine in Bonnet’s psychology is his theory of “traces” or “impressions” in the nervous system. According to Bonnet, every perception leaves a minute physical modification in the brain. Memory and imagination are explained as the reactivation of these traces, either spontaneously or by association. This allowed him to present a continuous account from sensation to complex thought while still insisting that a non‑material soul “accompanies” and experiences these bodily processes.

This model underlies his explanation of what later came to be known as Charles Bonnet syndrome. Bonnet observed his elderly grandfather, who had severe visual impairment but intact cognition, experiencing vivid visual hallucinations of figures, patterns, and scenes. Bonnet interpreted these as the mind’s re‑excitation of visual traces in the absence of adequate sensory input. In modern neurology and psychiatry, “Charles Bonnet syndrome” refers to complex visual hallucinations in people with significant vision loss but no major psychiatric or cognitive disorder, echoing Bonnet’s original description.

Bonnet’s broader metaphysical picture extends this psychophysical parallelism to all of nature. He defended a preformationist biology, arguing that all future organisms were already present in miniature in the original creation as nested germs. Development and the apparent rise of complexity in nature were, on this view, a process of unfolding what was already given, rather than of genuinely new forms emerging. This fit into his version of the great chain of being, where every creature occupies a determinate rung in a continuous hierarchy that ascends from the simplest organisms to humans and, beyond them, to higher spiritual beings.

In La palingénésie philosophique he elaborated a speculative doctrine of palingénesis—a cyclical renewal of beings in which souls progressively ascend this hierarchy through successive embodiments. Here Bonnet sought to combine empirical natural history with a hopeful eschatology: apparent suffering and imperfection in this life would be compensated by gradual moral and intellectual improvement across cosmic history.

Critics, both in his own time and later, argued that Bonnet’s heavy reliance on preformationism and a rigid cosmic hierarchy constrained his ability to account for evolutionary change, adaptation, and genuine novelty in nature. Others, however, highlighted his focus on graded continuity between mental and biological phenomena as an early, if speculative, anticipation of later naturalistic approaches to the mind.

Legacy and Reception

Bonnet’s contemporary reputation rested on his natural history, but his long‑term legacy is more pronounced in psychology and philosophy of mind. His careful description of visual hallucinations in the visually impaired secured his name in clinical terminology. Modern accounts of Charles Bonnet syndrome differ in detail from his own theory, yet they preserve his central insight that hallucinations can occur in mentally healthy individuals due to sensory deprivation and brain dynamics, rather than madness or moral failing.

In philosophy, Bonnet is often cited as a representative of 18th‑century psychophysiology, standing at the intersection of empiricist psychology and dualist metaphysics. Historians of philosophy note the affinities between his notion of neural “traces” and later ideas about engram-like memory storage and associative networks, even though the scientific framework has changed radically.

His biological and metaphysical speculations, particularly preformationism and his elaborate version of the great chain of being, declined in influence with the rise of 19th‑century cell theory, embryology, and evolutionary biology. From the perspective of modern science, these doctrines are generally regarded as obsolete. Nonetheless, scholars of the Enlightenment continue to study Bonnet as a figure who illustrates how early modern thinkers attempted to unify empirical research, theology, and speculative metaphysics.

Proponents of renewed interest in Bonnet argue that his work exemplifies a historically important effort to ground mental phenomena in physiological processes while preserving a spiritual dimension, revealing tensions that continue to inform contemporary debates in philosophy of mind and cognitive science. Critics maintain that the speculative and theological components of his system limit its direct relevance to present‑day theory. Yet there is broad agreement that Charles Bonnet provides an instructive case study in the transition from classical natural history to more modern conceptions of biology and psychology.

Bonnet died at his estate in Genthod, near Geneva, in 1793. His writings remain a significant resource for historians examining early modern attempts to integrate observations of the living body and the experiencing mind into a single, if highly ambitious, philosophical system.