Pietro d'Abano

Pietro d'Abano's standing in his own century rests on the Conciliator Differentiarum Philosophorum et Praecipue Medicorum, a book whose method is announced in its title. He set out the points on which the authorities disagree, Aristotle against Galen, the Greeks against their Arabic commentators, and worked through each difference until he could show it resolved or explain why it could not be. The work runs to more than two hundred such questions and was still being printed in the sixteenth century.

He had the equipment for it. He is reported to have travelled to Constantinople to read Greek medical and astronomical texts in the original, at a time when the Latin West met most of them only through translations of Arabic translations, and he produced Latin versions of his own. He taught at Paris in the 1290s and then returned to Padua, whose medical faculty was becoming the strongest in Europe.

His astrology sits inside that project rather than beside it. The Lucidator dubitabilium astronomiae treats astronomy and astrology as one discipline resting on a natural basis, and in medicine he took celestial timing as a physical factor acting on the body in the way that climate or diet do. That was a mainstream scholastic position in his generation rather than an esoteric one, and it is worth saying plainly, because his later reputation as a magician reads his work backwards through a book he did not write.

Twice the Inquisition took an interest in him. The first case appears to have lapsed. The second was under way when he died in 1316, and the tradition holds that his body was moved from its grave by friends before any posthumous sentence could be carried out on it. What the charges actually were is reported differently by different later writers and the surviving record is too thin to settle it. What is clear is that a natural philosopher arguing for celestial causation, in Padua, in that decade, was exposed.

The Heptameron, or Elementa Magica Petri de Abano, is the work that carried his name into modern occultism. It is short and practical: the hours of the day and night with their ruling angels, the circles to be drawn, the conjurations for each day of the week. It was printed in 1559, appended to the spurious Fourth Book of Agrippa's Occult Philosophy, and it is more than two centuries younger than the man on its title page.

The atlas keeps the ascription and marks it rejected rather than deleting it, because the false attribution is itself the historically important fact. It is how d'Abano entered the Solomonic tradition, why later grimoire writers cite him as an authority, and a clean example of what a famous name could do for a text that needed one. Who actually wrote the Heptameron is not known, and that gap is recorded as an open question rather than filled with a guess.