Girolamo Cardano

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Girolamo Cardano — Latinized as Hieronymus Cardanus, anglicized as Cardan — was an Italian physician, mathematician, and astrologer whose career spans the full range of sixteenth-century learning, from the algebra of cubic equations to the casting of horoscopes and the interpretation of dreams. Born in Pavia in 1501, the illegitimate son of a Milanese jurist, he rose from a disputed start to become one of the most sought-after physicians in Europe and one of its most prolific authors, leaving some two hundred works at his death in Rome in 1576.

His enduring place in the history of science rests on the Ars Magna of 1545, which gave the first printed general solution to the cubic and quartic — the work that opened modern algebra, and that embroiled him in a bitter priority quarrel with Niccolò Tartaglia, from whom one method had come under a pledge of secrecy. He wrote on mechanics (the universal joint that still bears his name is so called after him), on the natural world, and, in the Liber de ludo aleae, on the mathematics of dice and chance — among the earliest sustained reasoning about probability, though it appeared only long after he wrote it.

These pursuits were, for Cardano, of a piece with his astrology, not opposed to it. He held the heavens to be a legible order whose influences a careful observer could read, and he cast nativities throughout his life — including, notoriously, a horoscope of Christ, which numbered among the charges that saw him briefly imprisoned by the Inquisition in 1570. He compiled and published collections of horoscopes as case studies, treated his own life as data, and in the Somniorum Synesiorum libri set out an elaborate art of reading dreams for what the cosmos disclosed through them. Across his late writings he described a personal attendant spirit — a genius or daimon, in the long classical and Neoplatonic lineage of the guiding spirit — to which he attributed his warnings, his fortune, and the strange turns of his life.

Modern scholarship tends to read Cardano not as a credulous figure who also happened to do mathematics, but as a thinker for whom astral causation, medicine, and number formed one continuous science of nature; the boundary that later separated astrology from astronomy had not yet been drawn, and his contemporaries Pietro Pomponazzi and Jean Bodin argued the reach of celestial and demonic powers in the same key. What survives most vividly is the self-portrait. In De vita propria liber, written near the end, he set down his ailments, his gambling, the execution of his son for poisoning, his quarrels and dreams and the voice he believed accompanied him, with a candor unusual for any age. The book remains the closest thing to seeing a Renaissance mind take its own measure — a man who counted the stars and the dice alike, and was sure both were trying to tell him something.

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