Pierre Gassendi

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Pierre Gassendi was a French Catholic priest, astronomer, and philosopher whose life’s work was the rehabilitation of Epicurus — and whose place in the history of esotericism is that of its most careful early opponent. He was born on 22 January 1592 at Champtercier, a hamlet in the hills above Digne in Provence, and trained first at the college in Digne, then in philosophy at Aix-en-Provence and in theology at Avignon, where he took the doctorate in 1614. He entered holy orders in 1616 and was attached for the rest of his life to the cathedral at Digne, holding a canonry from 1614 and rising in 1634 to provost of the chapter. From that provincial base he built a correspondence that reached across Europe, and in 1645 he was named to the chair of mathematics at the Collège Royal in Paris, where he lectured on the new astronomy. He died in Paris on 24 October 1655, the great Epicurean synthesis on which he had labored for decades still unpublished.

The astronomer

The mathematics was not ornamental. On 7 November 1631 Gassendi watched the planet Mercury cross the face of the Sun — the first such transit ever recorded by a human eye — catching the tiny black disk by projecting the Sun’s image through a small telescope onto a sheet of paper in a darkened room. The event had been predicted by Johannes Kepler, and the match between the prediction and the speck of shadow on the paper is a fair emblem of the whole temper Gassendi would carry into philosophy: a claim about the heavens earns its keep by saying, in advance, exactly where to look and what will be seen there. He observed comets, mapped the Moon, measured the speed of falling bodies in defense of Galileo, and wrote the life of his patron and fellow observer Nicolas-Claude Fabri de Peiresc. He belonged, by temperament and by correspondence, to the loose republic of observers and calculators gathered around the Minim friar Marin Mersenne — the cell that also drew in René Descartes, Thomas Hobbes, and the partisans of the new astronomy. Within that circle Gassendi was the empiricist: less the builder of systems from first principles than the man who insisted the system answer to what the eye could check.

The Garden, baptized

His positive philosophy was a long act of recovery. Where the schools still taught a world of Aristotelian substantial forms and occult qualities, Gassendi proposed instead a universe of indivisible particles moving through empty space — the atomism of Epicurus and Lucretius, drawn from the doxographic record in Diogenes Laertius and from the hexameters of De Rerum Natura, and rebuilt piece by piece into something a Christian could hold. The reconstruction was deliberate and surgical. The ancient Garden had taught that the atoms were eternal, infinite in number, and self-moving, swerving by undirected chance through a cosmos with no governor and no providence; that the soul was itself corporeal and dissolved at death; that the gods, if they existed, paid the world no attention. Gassendi kept the particles and the void and discarded the rest. In his hands the atoms become finite in number, created out of nothing by God, and endowed with their motion by God — second causes set running by a first. The undirected swerve gives way to providence. And the human soul is split: its sensitive, animal part is material, a knot of fine and rapid atoms, but its rational part — the anima rationalis — is incorporeal and immortal, infused from outside the material order rather than emerging from within it. The cheerful materialism of the Garden is admitted at the door, searched, and stripped of exactly those doctrines that made it a scandal to the Church.

This was the labor of his life. He set it out first in his commentary on the tenth book of Diogenes Laertius, the Animadversiones in decimum librum Diogenis Laertii (Lyon, 1649), which carried his own Latin of Epicurus’s Principal Doctrines, and at last in the Syntagma Philosophicum, the full system in three parts — canonic, physics, ethics — that appeared only in the posthumous Opera Omnia of 1658. Its early articulation against the Aristotelians had come much earlier, in the Exercitationes Paradoxicae adversus Aristoteleos of 1624, a young man’s broadside against the reigning philosophy of the schools. The Aristotelian critique was not his alone: a century before, the Paduan Pietro Pomponazzi had argued that natural reason could not demonstrate the soul’s immortality and that the marvels credited to spirits had ordinary causes — a naturalist erosion of the schools from inside Aristotle’s own vocabulary. Gassendi worked the same seam from a different quarry, replacing the Aristotelian frame outright rather than turning it against itself.

The reach of knowledge

Beneath the physics lay a theory of what knowing can do, and it is here that Gassendi is most distinctive. He held a measured, constructive skepticism — a via media, he called it, between two failures. The dogmatist claimed to read off the inner essences of things, the hidden natures behind appearances; the Pyrrhonist, despairing of essences, suspended judgment about everything and ended in paralysis. Gassendi denied the first and refused the second. The mind, he argued, has no window onto the inside of nature: it never grasps the essence of fire or of gold, only the appearances they present and the signs they leave. But appearances and signs are not nothing. From them careful observation can build a knowledge of how things behave — provisional, corrigible, never certain to the depths, yet genuinely answerable to the world. Knowledge runs exactly as far as observation reaches and the cautious inference it licenses, and no further. He had absorbed the arguments of the ancient skeptics, recovered in his century through Sextus Empiricus and pressed into service by the libertins érudits, and turned their corrosive force into a discipline rather than a surrender. The same temper drove his most famous quarrel with Descartes: in the set of objections printed as the fifth in Descartes’s Meditations (1641), Gassendi, prompted again by Mersenne, refused the Cartesian leap from thinking to an immaterial thinking substance, pressing the empiricist’s demand that knowledge keep its feet on the evidence of the senses.

The case against Fludd

It was this temper — the insistence that a claim about nature must cash out in something observable — that set Gassendi against the Hermetic and Paracelsian current then at its height. Its most ambitious English exponent was the physician Robert Fludd, whose vast Utriusque Cosmi Historia (1617–1621) read the universe as a single graduated harmony: the macrocosm and the microcosm mirroring each other rung for rung, the same fire above and below, the body of man scaled to the body of the world, scripture and alchemy and the music of the spheres folded into one structure that Fludd held to descend from Hermes Trismegistus through the prisca theologia. The cosmos was a divine monochord, a single string stretched by God’s hand from Earth to Empyrean; the relation of form to matter at each level was figured in interpenetrating pyramids of light and darkness. Fludd had already lost one great exchange over this apparatus — to Kepler, who between 1619 and 1622 dismissed the pyramids as pictures masquerading as proofs, ratios that admitted no number a measurement could check. He had been censured by Mersenne, whose Quaestiones in Genesim (1623) marked him as a magician smuggling pagan cosmology into the Mosaic account.

Gassendi entered at Mersenne’s urging, and entered as a philosopher. In 1630 he published the Epistolica Exercitatio, in qua principia philosophiae Roberti Fluddi medici reteguntur (Paris: Sébastien Cramoisy) — the work reissued, in the posthumous collected edition, under the heading Examen Philosophiae Roberti Fluddi medici, the title by which it is often cited. Its method matched its matter. Gassendi first set out Fludd’s doctrine fairly, in Fludd’s own terms, without the abuse Mersenne had heaped on it; then he took it apart point by point. His charge was not, in the end, the charge of impiety, though he registered that too. It was that the whole edifice explained nothing. The correspondences could be asserted but never tested. A system that accounts for everything by likeness — this resembles that, the heart is the sun of the body, the seven metals answer to the seven planets — predicts nothing in particular, forbids no observation, survives every result equally, and so dissolves on contact into metaphor. The monochord and the pyramids were not measurements dressed as images; they were images that could never become measurements, because no reading of the sky or the body could ever confirm or refute them. Fludd answered the next year in his Clavis Philosophiae et Alchymiae Fluddanae (1633), insisting that proportion and picture say what calculation cannot reach. The two men were arguing past each other, because they disagreed about what counts as evidence — and that disagreement, not the doctrines, is the real content of the collision.

Scholarship and sources

The 1630 polemic is the hinge of Gassendi’s standing in the history of esotericism, and its bibliography is well established. The first issue, Petri Gassendi Epistolica Exercitatio, in qua principia philosophiae Roberti Fluddi medici reteguntur (Paris: Cramoisy, 1630), is cataloged with its full title and imprint in the union record at WorldCat; it was later folded into volume III of the Opera Omnia (Lyon, 1658) as the Examen Philosophiae Roberti Fluddi, the title by which it is most often cited. The standard modern English account of Gassendi’s whole program is Lynn Sumida Joy’s Gassendi the Atomist: Advocate of History in an Age of Science (Cambridge, 1987); the early bibliography and the chronology can be checked against the older but serviceable life at MacTutor and the 1911 article at Wikisource. The texts on the far side of the quarrel — Fludd’s printed corpus and the de Bry engravings that carry his cosmology — are all in the public domain, the Utriusque Cosmi among them. The Epicurean substrate Gassendi rebuilt rests on the same documentary base any reader can consult: the Principal Doctrines and the three letters preserved in Diogenes Laertius Book X, available in the fully public-domain translations of C. D. Yonge (1853) and R. D. Hicks (Loeb, 1925), and the De Rerum Natura of Lucretius in the prose of H. A. J. Munro (1886). The skeptical arsenal Gassendi turned to constructive ends descends from Sextus Empiricus, whose first-century-of-print recovery — the Latin renderings of Estienne (1562) and Hervet (1569) and the Greek editio princeps of 1621 — fed the same generation of French libertins érudits to which he belonged. One strand of his target’s pedigree had already been cut by philology: the claim that the Hermetic writings preserved a wisdom older than Moses, on which Fludd leaned without qualm, had been undone in 1614 when Isaac Casaubon dated the corpus to late antiquity — a result Fludd never acknowledged, and one that Gassendi’s own emphasis on testable inference quietly reinforced from another direction.

What he changed

Gassendi sits at a seam. He was neither the last of the Renaissance polymaths nor quite the first of the moderns, but a man working the joint between them: an ordained Catholic priest who said Mass and held a cathedral provostship, and at the same time the reviver of a pagan physics whose atoms would pass, through Walter Charleton’s English digest of 1654, into the hands of Robert Boyle and Isaac Newton, and whose empiricism would find its fuller voice a generation later in John Locke. His theology kept one foot in the older world even as his method walked into the new one. The deepest mark he left on the argument with the Hermetic synthesis was a shift in the question itself. For Mersenne the trouble with Fludd had been that he was a magician — impious, a smuggler of pagan cosmology into scripture, a man to be ruled out of the licit field. Gassendi moved the test. The question he put to the cosmology of correspondences was not whether it was forbidden but whether it forecast anything an observation could meet — and a doctrine that no measurement could ever touch, neither to confirm nor to break, had nothing left to answer with. To be ruled impious is to be silenced by an authority that might be mistaken; to be shown untestable is to be left, on one’s own terms, with nothing to say. That second verdict is the one Gassendi handed forward, and it is a harder one to appeal.

→ Related: Paracelsus · Aristotle · Tommaso Campanella · Hermes Trismegistus · Robert Fludd · Marin Mersenne · Rene Descartes · Galileo Galilei · Isaac Newton · Johannes Kepler · Pietro Pomponazzi · John Locke · Isaac Casaubon · Prisca Theologia · Rosicrucianism