Play: D'Alembert's Dream

Overview
D'Alembert's Dream (1769) is a set of dramatic philosophical dialogues in which Denis Diderot tests a boldly materialist view of life, mind, and nature. Posed as conversations among real Enlightenment figures, it uses wit and stage-like exchanges to probe whether matter can feel, organize, and think without recourse to a separate soul. Written in 1769 and published posthumously in 1830, it fuses natural history, experimental physiology, and speculative metaphysics into a meditation on what an organism is and how consciousness arises.

Structure and characters
The work unfolds in three linked dialogues. In the opening exchange, Diderot spars with his friend, the mathematician Jean le Rond d'Alembert, teasing out the scandalous thesis that sensibility is an inherent property of matter, not a gift from an immaterial soul. The title piece follows: d'Alembert, feverish and dozing at the salon of his companion Mlle de Lespinasse, mutters in dreamlike fragments while the physician Théophile de Bordeu interprets his words and spins them into a theory of living organization. A concluding conversation develops the medical and moral implications of this theory, turning to reproduction, heredity, and the social ordering of bodies and desires.

Central arguments
Diderot advances a monist, dynamic account of nature. Living beings are not machines driven by an external spirit but ensembles of active, responsive particles whose organization produces sensation and thought. He borrows from contemporary physiology the imagery of vibrating fibers and communicating organs, treating the body as a swarm or hive whose members coordinate without a commander. From this perspective the self is an emergent consensus, a fluctuating center of experience maintained by the organism’s ongoing exchanges with its environment.

The dream device lets Diderot entertain ideas that exceed cautious daytime reason. As d'Alembert murmurs about bees, polyps, and strings, Bordeu extrapolates: matter has degrees of sensibility; when arranged in complex networks it becomes capable of memory and imagination; when disarranged by illness or death, those capacities dissolve back into the general flux. Generation does not copy a fixed blueprint but proceeds by epigenesis, gradual organization out of living materials, allowing for variation, monstrosity, and the open-ended evolution of forms. If the organism is a polity of tissues, morals and institutions should respect its plasticity rather than impose mechanical or theological abstractions.

This materialism dissolves the soul–body dualism. There is no immortal, separable seat of mind; what people call the soul is the concert of bodily processes. Sensation pervades the continuum from the simplest living units to complex animals, differing in degree more than kind. Sleep and dreams, far from being gateways to another realm, exhibit the same bodily logic as waking life: a reassembly of impressions as the system vibrates along old tracks.

Imagery and tone
The writing shifts between salon banter, clinical case talk, and visionary speculation. Diderot delights in analogies: the organism as a spider web of nerves, a choir of voices, a republic of collaborating parts. Mlle de Lespinasse’s presence keeps the scene social and skeptical; Bordeu’s medical pragmatism grounds the flight of ideas in observation; d'Alembert’s delirium licenses bold hypotheses while also exposing their limits.

Legacy
The dialogues anticipate later biology and philosophy: epigenesis against preformationism, emergentism against Cartesian mechanism, distributed cognition against a unitary ego. They also register Enlightenment tensions, between science and religion, freedom and determinism, social custom and bodily truth. By dramatizing thought as conversation and dream, D'Alembert's Dream turns speculative physiology into theater, making the nature of life and mind a living scene rather than a doctrinal lecture.