A Treatise of Human Nature appeared anonymously in 1739 and 1740, in three volumes, and sold nothing; no second edition came out in its author's lifetime. Its argument is still the most unsettling thing in English philosophy. Newton had accounted for the tides and the planets with a few laws and a mathematics anyone could check, and by the 1730s the next question was obvious: could the same experimental method be turned on the instrument doing the checking, the human mind? In Britain that was not an academic question, because moral philosophy was taught by clergymen, and the reasoning that held morality and religion together ran through reason itself — reason proved a first cause, read design off the natural world, and underwrote the assumption that tomorrow would behave like yesterday. Nobody had audited the credentials.
He audited them, and he did it before he was thirty. He entered the University of Edinburgh at about eleven and left at fifteen without a degree; his family expected law, and he read Cicero instead. At eighteen the studying broke him. His ardour for philosophy went out in a matter of weeks, stayed out for nine months, and turned into physical symptoms that a physician diagnosed as the occupational complaint of scholars, prescribing bitters, a pint of claret a day and long rides. In 1734 he left for La Flèche in Anjou, a market town whose Jesuit college had educated Descartes, and lived cheaply there for three years writing one book.
Watch one billiard ball strike another. You see the first move, then the second; you never see the making-happen, and no amount of logic gets you from what has always happened to what must happen next. Cause and effect, Hume concluded, is a habit of expectation laid down by repetition — custom, not proof. He turned the same instrument on the self and found a rapid succession of perceptions with no observer standing behind them; and on morality, where he noticed that writers slide from statements of fact to statements of obligation without ever showing the join. He was not demolishing for sport: habit works, he insisted, and is simply not what we thought it was.
The positions in it cost him a career: Edinburgh's clergy blocked his candidacy for a chair in 1745 on the charge of atheism. Glasgow passed him over for the chair of logic in 1751 — his friend Adam Smith, who had vacated that chair, opposed the appointment for fear of public opinion. The Church of Scotland moved to excommunicate him in 1755 and 1756 and failed. As keeper of the Advocates Library from 1752 he was censured by his own curators for ordering three indecent French titles; he never taught a class.
His fame and his income came instead from six volumes of The History of England, and to his contemporaries that is who he was: a historian with a dangerous sideline.
Kant credited him with breaking the spell of a dogmatic sleep, and rebuilt metaphysics to answer him. The Dialogues Concerning Natural Religion were too dangerous to publish alive; Smith declined the task, and Hume's nephew brought them out in 1779, three years after the death. The problem of induction he set has never been solved. Nor has the argument around him stayed comfortable: in 2020 Edinburgh stripped his name from a campus tower over a footnote on race he added to an essay in 1753.