Gerolamo Cardano is one of the most surprising figures of the Italian Renaissance. In the history of mathematics he is remembered for publishing the solution of cubic equations; in mechanics his name survives in the "cardan joint"; in medicine he was one of the most sought-after practitioners in Europe. Yet he was also a convinced astrologer, an interpreter of dreams and omens, a man who believed he was accompanied by a familiar spirit. His figure shows how porous the boundaries between science and the occult arts were in the sixteenth century.
A difficult youth
Cardano was born in Pavia in 1501, the illegitimate son of Fazio Cardano, a Milanese jurist and mathematician and a friend of Leonardo da Vinci. His childhood was marked by illness and a difficult relationship with his family. He studied medicine at Pavia and Padua, where he graduated, but for years the College of Physicians of Milan refused to admit him because of his illegitimate birth.
For a long time he lived in poverty, practising medicine in a small town near Padua and gambling at dice and chess to support himself. This experience gave rise to the Liber de ludo aleae, one of the first mathematical studies of probability in games, published only in the seventeenth century.
The mathematician of the Ars magna
Having finally won recognition in Milan, Cardano became a famous physician and professor. In 1545 he published the Ars magna, one of the founding texts of modern algebra, in which he set out methods for solving equations of the third and fourth degree.
The publication sparked one of the most famous controversies in the history of mathematics. The method for cubic equations had been revealed to him by Niccolò Tartaglia, who claimed to have communicated it under an oath of secrecy. Cardano replied that he had discovered that the solution had already been found by Scipione del Ferro, and in the book he credited both; the method for the fourth degree belonged instead to his pupil Ludovico Ferrari.
The encyclopaedias of nature
Cardano wrote two great works of natural philosophy that were widely circulated:
- De subtilitate (1550), an encyclopaedia of natural and artificial things, from metals to animals, from machines to demons;
- De rerum varietate (1557), a continuation gathering further wonders, secrets and observations.
In these books accurate technical descriptions, such as that of the suspension system that bears his name, coexist with beliefs typical of the time about sympathies between things, prodigies and spirits.
The astrologer
Astrology held a central place in Cardano's thought. He wrote an extensive commentary on Ptolemy's Tetrabiblos, the foundational text of ancient astrology, and collections of horoscopes of famous people, with which he meant to prove the validity of the art by comparing natal charts with real lives.
Two horoscopes made him particularly well known:
| Horoscope | What happened |
|---|---|
| Edward VI of England | In 1552 Cardano, visiting England, predicted a long life for him; the young king died the following year, aged fifteen |
| Jesus Christ | In his commentary on Ptolemy he cast Christ's natal chart, provoking the charge of subjecting the Saviour's life to the influence of the stars |
The case of Edward VI is instructive: Cardano himself, in later editions, tried to explain the error, showing how hard it was for astrology to pass the test of facts.
Dreams, omens and the familiar spirit
In the Somniorum Synesiorum (1562) Cardano dealt with the interpretation of dreams, also gathering personal experiences. He was interested in metoposcopy, divination from the lines of the forehead, and in his autobiography he told of omens and of a protective spirit that supposedly accompanied him, as, according to him, had also been the case with his father.
Tragedies and trial
His last decades were marked by misfortune. In 1560 his eldest son, Giovanni Battista, was executed for poisoning his wife, and the scandal engulfed the father too. In 1570, while teaching at Bologna, Cardano was arrested by the Inquisition. He was released after some months, but was forbidden to teach and publish.
He moved to Rome, where he received a pension from the pope and spent his last years writing the De vita propria, an autobiography of exceptional frankness, published in 1643. He died in Rome in 1576. A legend, reported by later authors and unproven, holds that he let himself die to confirm the date of his own death foretold by astrology.
In short
- Gerolamo Cardano (1501-1576) was a physician, mathematician, natural philosopher and astrologer.
- In the Ars magna (1545) he published the solution of equations of the third and fourth degree.
- He commented on Ptolemy and compiled famous horoscopes, including the mistaken one of Edward VI.
- Arrested by the Inquisition in 1570, he wrote his autobiography De vita propria in Rome.
