David Hartley

David Hartley: The Physician Who Wired the Soul

In 1791 William Blake engraved the frontispiece for a new edition of a forty-year-old book about the human nervous system. The book was *Observations on Man, His Frame, His Duty, and His Expectations*, and its author had been dead since 1757. That a visionary poet should be enlisted to illustrate a physician's treatise on nerve vibrations captures the strangeness of David Hartley's achievement: he wrote what looks like a manual of neurology and what reads, by its second volume, like a promise of universal salvation. Joseph Priestley, who discovered oxygen, said the book "contains a new and most extensive science," and that he was "more indebted to this one treatise, than to all the books I ever read beside; the scriptures excepted."

A Yorkshire Sizar

Hartley was the son of an Anglican clergyman, born in June 1705 near Halifax in the West Riding. He went to Bradford Grammar School and in 1722 entered Jesus College, Cambridge, as a sizar — the poorest rank of undergraduate, expected to earn keep by service. There he studied under Nicholas Saunderson, the blind Lucasian Professor of Mathematics, an arrangement that mattered more than a footnote: Hartley's lifelong fascination with how the senses substitute for and coordinate with one another, how a blind man builds a world, began at close range. He took his BA in 1726 and his MA in 1729.

Then came the decision that shaped his career by closing a door. Ordination required subscription to the Thirty-nine Articles of the Church of England. Hartley would not sign. He could not accept the doctrine of eternal punishment — "nothing is so irreconcilable [with] Reason," he later wrote — and so the clerical living that would have been the natural landing place for a Cambridge man was forfeit. He became a physician instead, and the loss of the pulpit is arguably why the *Observations* exists at all.

The Doctor in Practice

Hartley practised at Newark, where in 1730 he became the first layman to serve as Master of the Magnus Grammar School, then at Bury St Edmunds, then London from 1736, and finally Bath from 1742. He married Alice Rowley in 1730; she died in childbirth, leaving a son, David Hartley the Younger, who would grow up to sign the treaty ending the American War of Independence. In 1735 he married Elizabeth Packer, of a wealthy family holding Donnington Castle House, and had two more children.

His medical work was not incidental to his philosophy; it was of a piece with it. In 1733 he published a pamphlet urging smallpox inoculation on the town of Bury, arguing the case statistically — weighing public benefit against private risk — in the company of Hans Sloane and James Jurin at the Royal Society, to which he was himself elected. From 1736 he suffered from bladder stones, an affliction of medieval brutality in an age before anaesthesia, and turned his own agony into research. He published *Ten Cases of Persons who have Taken Mrs. Stephens's Medicines for the Stone* in 1738, persuaded Parliament to buy Joanna Stephens's secret formula for £5,000, and worked with Stephen Hales to establish its active ingredients as slaked lime and Alicant soap. Hales took the Copley Medal for the work in 1739; Hartley published the findings in Latin, as *De Lithontriptico*, at Basel and Leiden in 1740. He was known to physicians across Europe, and was a vegetarian. When he died at Bath in August 1757, the *London Evening Post* recorded that he was "much lamented by the Poor."

Vibrations

The *Observations* appeared in 1749, published by the novelist Samuel Richardson. Its first part is a physiology of mind. Hartley proposed that sensation consists of vibrations among minute particles in the medullary substance of the nerves — not Descartes's hydraulic tubes of animal spirits but Newton's aetherial medium, transmitted through solid nerve filaments. Moderate vibrations register as pleasure; violent ones, which break the continuity of the nerve, as pain. Every vibration leaves behind a fainter residue, which Hartley called a *vibratiuncle*, and these faint traces are ideas. Memory is the persistence of a dying tremor.

Onto this physical substrate he mapped a psychological law: association. Building on Locke's blank slate, he proposed that contiguity — of sensations occurring together or in sequence — was the single universal mechanism by which mind grows from raw sensation into thought, language, morality and belief. He was unusually good on a subject other philosophers ignored: skilled physical action. He distinguished motions "originally automatic," like the heartbeat, from "secondarily automatic" ones — practised skills that sink below consciousness — and from "decomplex" sequences that assemble into speech or piano playing. Anyone who has learned an instrument recognises the description; it took a century and a half for psychology to catch up with it.

The book is enormous and unruly, a vast haystack of observations taking in phantom limbs, savant abilities, blindness and deafness. Its second part is not physiology at all but a moral and spiritual architecture: six schemas of intellectual pleasure and pain — Imagination, Ambition, Self-Interest, Sympathy, Theopathy (his own coinage, for feelings arising from ideas of God) and the Moral Sense — that reshape one another as a person develops. Association carries the individual from sensuality toward what Hartley called the "annihilation of self," and carries humanity, eventually, to universal happiness. He extended the theory to animals, arguing they differ from us in degree and not in kind, which demolished the Cartesian animal-machine.

Why David Is Called a Genius

Hartley has a defensible claim to the word, but a specific one. He was not a dazzling reasoner; his prose is patient to the point of monotony and he proceeds in propositions and corollaries like a geometer. The genius is architectural. He was the first to attempt a complete causal bridge from vibrating matter to conscience — to say, in one continuous argument, that a physical event in a nerve becomes a memory, becomes a habit, becomes a moral judgment, becomes the love of God. Albrecht Koschorke has described this as cybernetics *avant la lettre*, an account of how increasing complexity generates entirely new qualities of mind. Basil Willey admired the rare blend of scientific ardour with religious certainty, and Hartley's decision to derive religion "not from the starry heavens, but from a study of human psychology."

The counter-case is real and was made early. Leslie Stephen judged in 1876 that Hartley "could not get beyond the very first step," since executing his method properly would demand a full physiology of the brain that his century could not supply — the vibration theory was, on the evidence available, closer to inspired guesswork than science. John Stuart Mill, whose own school claimed Hartley as founder, called the *Observations* merely "a sketch, though an eminently suggestive one." Coleridge, who had named his eldest son David Hartley Coleridge and sat for a portrait clutching the book, turned on it in *Biographia Literaria*, arguing that its mechanism left the mind wholly passive. Thomas Reid thought it stood on the threshold of materialism. The honest verdict: Hartley was a synthesist of extraordinary reach whose central mechanism was wrong, and whose framing of the problem was so nearly right that psychology spent the next two centuries inside it.

Legacy

Priestley's advocacy carried Hartley into the dissenting academies, where a generation of radicals studied him; when Priestley fled England for America in 1794 after a Church-and-King mob burned his house, he read the *Observations* at sea for consolation. Harriet Martineau, at nineteen, found it "perhaps the most important book in the world to me, except the bible." James Mill, John Stuart Mill, Alexander Bain and William Carpenter built association psychology on his foundation. Modern readers find in him an early neuroscientist, an early cognitive theorist of learning, and a heretic who reasoned his way from nerve fibres to the conviction that in the true system of things "the voice of nature is an universal chorus of joy and transport."