René Descartes

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René Descartes (Latinized Cartesius, 1596–1650) was a French philosopher and mathematician whose redescription of nature as matter in motion did much to end the world-picture that Renaissance magic and hermeticism had assumed. He is remembered for the method of systematic doubt, for the single certainty he claimed to reach through it — cogito, ergo sum, I think, therefore I am — and for splitting the world into two kinds of stuff: mind, which thinks, and body, which is sheer extension and obeys mechanical law.

He was born on 31 March 1596 at La Haye en Touraine, a small town since renamed in his honor, and schooled at the Jesuit college of La Flèche, where the curriculum still ran along Aristotelian lines and where he later said he had learned chiefly how much remained doubtful. He took a law degree at Poitiers, then left the lecture-hall for what he called the great book of the world, attaching himself as a gentleman volunteer to the armies then mustering in the Low Countries and the German lands at the opening of the Thirty Years’ War. Most of his mature life was spent not in France but in the Dutch Republic, where he moved in 1628 and stayed two decades, shifting lodgings often and writing his major works in a quiet he guarded jealously. He died far from there, in Stockholm, on 11 February 1650, of a chill that turned to pneumonia, having gone north at the summons of the young Queen Christina of Sweden, who required her philosophy lessons before dawn in a cold he never adjusted to.

The mechanical world and the magical one

The division of mind from body is the part of his work that bears on esoteric history. The inherited cosmos of the magi was alive throughout: stars with influences, herbs with virtues, hidden correspondences binding the human being to the heavens, a soul of the world running through all of it. Descartes drained that animacy from physical nature. In his account, body is dead extension, a thing defined by length, breadth, and depth and nothing else, fully explicable as machinery and obeying laws of motion that hold as much for a falling stone as for the circulation of the blood; mind is walled off on the other side as the one thing that thinks and is not extended. The planets push, they do not signify. He did not refute astrology or alchemy so much as leave them no room to stand: a universe of pure geometry and impact has no place for a star’s secret virtue or a metal’s striving toward gold. Scholarship has long treated this — together with the parallel work of Francis Bacon and Galileo Galilei — as a turning point after which the magical sciences slowly lost their standing as knowledge, however long they went on being practiced.

The redescription was not a stray polemic but the cosmology that follows from his physics. Where the older natural philosophy read the world as a tissue of likenesses and sympathies — a book of signatures in which everything pointed beyond itself — Descartes asked of any body only its size, shape, position, and motion, the properties a mathematician can handle, and ruled the rest out of nature as qualities the mind projects. A thing no longer meant; it merely moved. The whole apparatus of occult qualities, of agents acting at a distance through hidden affinity, he regarded as an explanation that explained nothing, a name for ignorance dressed as knowledge. This is why his cosmos and the hermetic one cannot share a roof: one is a web of correspondences, the other a clockwork.

The clockwork was meant literally. Descartes held that the same principles of matter and motion that govern a mill or a fountain govern the heavens, the tides, magnetism, and the body of every animal; in his physics the planets are carried not by intelligences or by the tug of sympathy but by vast whirlpools, the vortices, of a subtle matter filling all space, since he allowed no void. Light is pressure transmitted through that plenum, not a quality streaming from a luminous source. The living animal is an automaton, its motions explicable as the play of fluids through pipes; even much of human physiology belongs on the body’s side of the divide, leaving the mind a far smaller domain than the older psychology had granted it. For a tradition that had located will and meaning throughout nature — in the star that inclines, the stone that heals, the metal that ripens toward perfection — this was not a rival theory of the same world but the abolition of that world’s grammar. There were no longer any sentences in things to read.

The method, the cogito, and the two substances

His procedure was to doubt everything that could be doubted and to see what survived. The senses deceive; the most certain mathematics might be the work of a deceiving demon; even the conviction of having a body could be a dream. What could not be doubted away was the doubting itself, for to doubt is to think, and to think one must exist — cogito, ergo sum. He first set the move down in French, in the Discourse on the Method of 1637, as je pense, donc je suis, deliberately writing in the vernacular to reach beyond the schools; he developed it at length in the Latin Meditations on First Philosophy of 1641, and the exact formula cogito, ergo sum enters his published Latin in the Principles of Philosophy of 1644. From that single fixed point he rebuilt: a self whose essence is thought, a God whose veracity guarantees that clear and distinct ideas are true, and a material world recovered through reason rather than the unreliable senses.

The two substances follow. Mind is res cogitans, a thinking thing, unextended and indivisible; body is res extensa, an extended thing, divisible and inert. They are really distinct, which is what licenses the mechanical treatment of all of physical nature — the heavens, the weather, the living animal, the human body itself, all of it matter in motion without purpose or sympathy. The cost was the seam between them. If mind and body share no attribute, how does a decision move an arm, or a wound arrive in the soul as pain? Descartes located the meeting point in the pineal gland and left the mechanism obscure, bequeathing the mind-body problem to everyone who came after. His last book, the Passions of the Soul of 1649, written partly out of his correspondence with Princess Elisabeth of Bohemia, who pressed him hardest on exactly this difficulty, tried to map how the body’s motions register in the mind as emotion without ever closing the gap. The school of thought that grew from these terms is treated under Cartesianism.

The hermetic youth he turned from

The irony, much noted, is how close his own beginnings ran to the world his philosophy emptied out. As a young man in the armies of Germany during the opening of the Thirty Years’ War, in the winter of 1619, he shut himself in a heated room — the German Stube, a stove-warmed chamber he called a poêle — and on the night of 10–11 November dreamed three vivid dreams, one of them shot through with a thunderclap and a scattering of sparks, that he took as a sign of his vocation and as the disclosure of the foundations of a marvelous science. This is the founding scene of his philosophy by his own later telling. He recorded it in an early private notebook he titled the Olympica, now lost, which his first biographer, Adrien Baillet, paraphrased in the Vie de Monsieur Des-Cartes of 1691; the dreams survive only at that second hand.

The same years saw the Rosicrucian manifestos — the Fama Fraternitatis of 1614, the Confessio of 1615, the Chymische Hochzeit of 1616 — circulating through the German lands and promising a universal reformation of learning, piety, and the hidden arts. Descartes, then a young seeker of method passing through the very country where the call had gone out, is reported to have tried to find the unseen Brotherhood that issued it, without success; in Germany he met the Ulm mathematician Johann Faulhaber, who had publicly professed sympathy with the brethren. On his return to Paris in 1623 the suspicion followed him that he had joined the order, and Baillet preserves the answer offered against the rumor: that Descartes could not be one of the Invisibles, since he showed himself plainly about town, visible to all — the very invisibility ascribed to the fraternity being, as the joke ran, the reason no one could find them.

How much weight the episode carries is genuinely contested. The dreams are attested only through the lost notebook Baillet paraphrased; the Rosicrucian contact is rumor worked up by his enemies and by later occult writers as much as by historians, and Frances Yates wove it into a larger thesis about a Rosicrucian moment in early-modern thought that not all scholars accept. What the episode marks is real enough — that the man who helped build the mechanical universe came up through the same ferment of hermetic and Rosicrucian hope as the figures his philosophy displaced, sought the very Brotherhood whose program he would render unthinkable, and emerged from it pointed the other way. The seeker of a single restored wisdom became the architect of a method that needed no wisdom but its own.

The afterlife of the split

His mature thought set the terms for a century of argument, and the most powerful replies came from within his own vocabulary. Baruch Spinoza, schooled on the Principles — the one book he published in his lifetime under his own name was an exposition of Descartes — pressed the dualism toward a single substance, Deus sive Natura, of which thought and extension are only two attributes, collapsing the two kinds of stuff into one and the personal Creator into nature itself. Nicolas Malebranche, the Oratorian who read Descartes’s Treatise on Man with such excitement that he had to keep setting the book down, took the seam between mind and body and cut it entirely: created things have no causal power at all, God alone acts, and what we call cause is only the occasion on which he acts — the doctrine of occasionalism, paired with the claim that we see all things in God. Blaise Pascal, Descartes’s near-contemporary and a mathematician of the first rank, went the other way and recoiled, judging the whole project useless and uncertain and reaching instead for a God known by the heart rather than demonstrated — the God of Abraham, not of the philosophers. The mechanical physics, meanwhile, passed by way of these debates toward Isaac Newton, whose mathematical natural philosophy would supersede Descartes’s vortices even as it kept his ambition of a world reduced to law.

Across the longer history of Western esotericism his name has come to stand for the loss it laments. Where the Renaissance had held a cosmos brimming with sign and sympathy — the cosmos of Giordano Bruno’s infinite living worlds, of the Corpus Hermeticum’s ensouled universe, of the magus who read the heavens and acted through them — Descartes left a nature of inert extension in which nothing answers, nothing means, and nothing can be moved by likeness. He shares this office with Marin Mersenne, his foremost correspondent, though the two cut at the magical synthesis from opposite directions: Mersenne the friar who fought it in print as impiety and fraud, Descartes the metaphysician who simply built a world with no place for it to be true. Mersenne argued the case; Descartes removed the ground beneath it.

Texts, biography, and scholarship

The chief published works form a tight sequence. The Discourse on the Method (Leiden, 1637) appeared in French as the preface to three scientific essays on optics, meteorology, and geometry, the last of which founded analytic geometry; the Meditations on First Philosophy (Paris, 1641) circulated with a famous set of objections by leading thinkers — among them Pierre Gassendi, Thomas Hobbes, and Antoine Arnauld — that Marin Mersenne gathered and forwarded; the Principles of Philosophy (1644) laid out the whole system; the Passions of the Soul (1649) closed it. All are long out of copyright and available in full across the open-access scholarly repositories. The encyclopedia’s own Library hosts the Corpus Hermeticum, the ensouled cosmos against which Descartes’s clockwork is most sharply read.

The indispensable early life is Adrien Baillet’s two-volume La Vie de Monsieur Des-Cartes (Paris, 1691), the source — for the dreams, the Olympica, and the Rosicrucian rumor — that every later biographer mines and second-guesses; the first volume can be consulted at the Bibliothèque nationale de France’s Gallica digital library. The modern standard intellectual biography is Stephen Gaukroger’s Descartes: An Intellectual Biography (Oxford, 1995), which treats the 1619 episode with care and skepticism. The standard English text is the three-volume Philosophical Writings of Descartes, translated by John Cottingham, Robert Stoothoff, Dugald Murdoch, and (for the correspondence) Anthony Kenny (Cambridge, 1984–91). For an accessible scholarly overview the Stanford Encyclopedia of Philosophy and the Internet Encyclopedia of Philosophy both carry full entries with bibliographies. The contested Rosicrucian thread is set in its larger frame by Frances Yates’s The Rosicrucian Enlightenment (London, 1972); the philological ground for the manifestos themselves is Carlos Gilly’s Cimelia Rhodostaurotica (Amsterdam, 1995), which corrects much of the older legend.

What the new philosophy took from the world it described was not a god or a star but a kind of speech. The Renaissance cosmos had been legible — every herb a word, every conjunction a sentence, the whole of it addressed to a reader who could learn to act on what he read. After Descartes the page is blank of all that. Matter still turns, the planets still wheel on their courses, but they no longer say anything; and the soul that once stood in correspondence with them is left thinking, certain of itself, and with nowhere in the physical world to belong.

→ Related: Francis Bacon · Galileo Galilei · Benedictus De Spinoza · Nicolas Malebranche · Blaise Pascal · Marin Mersenne · Cartesianism · Rosicrucianism · Renaissance Magic · Dualism · Soul · Isaac Newton · Giordano Bruno · Astrology · Alchemy · Corpus Hermeticum