The erosion of astrology

Astrology was first a scientific subject, rather than a superstition. It arose from the application by the Ancient Greeks of philosophical and scientific structure to data first collected by the Babylonians. This Greek tradition was nurtured in the Islamic world and was recovered by the West in the 12th and 13th centuries, largely from Arabic sources, along with much of Greek philosophy, maths and medicine.

Astrology was the practical application of astronomy. There was no point in knowing the mathematical equations to describe the motion of the planets unless you could do something useful with that knowledge. Events that affected whole kingdoms could be plotted. Horoscopes could be cast at the birth of a child and astrology could inform decisions. It was taken as scientific truth that changes in the world were caused by changes and configurations of the planets and stars.

From the 13th century onwards universities assimilated astrological knowledge. Astrology is taught as part of astronomy, which was one of the liberal sciences, and also as an important element of medical education. Copernicus learned his astronomy as a medical student in Padua. The belief that astrological predictions could be made more accurate if the movements of the heavenly bodies were known more accurately, prompted intellectual advances, such as the revisions of tables of planetary movement, the spread of Arabic numerals to facilitate calculation, and innovations in measuring instruments.

The most persuasive scientific criticism of astrology was that it could not be divined precisely enough. The basic premise of stellar influence on earthly change was accepted. That astrology did eventually fall out of fashion was probably largely due to the fact that, belonging at once to mathematics, physics and psychology, it proved too all-embracing to fit into one of the accepted disciplines of university teaching. The replacement of a geocentric universe with a heliocentric one was not in itself sufficient to dislodge it from its scientific respectability.

Charles Burnett is professor of the history of Arabic/Islamic influence in the Middle Ages at the Warburg Institute, University of London, and a leading authority on medieval astrology Interview by Steve Farrar.