INTRODUCTION

In medieval thought, the heavenly bodies held the highest status among all the material bodies. Whatever the specific philosophical or religious orientation of a person, he (or, much more rarely, she) believed that the stars and the planets (as well as the spheres to which they are affixed) were made of a noble “fifth matter,” distinct from the four sublunar elements with which it did not interact. The heavenly bodies were therefore excluded from the cycles of generation and corruption: They were usually taken to be eternal, and as such they were regarded as the most noble existents. It was furthermore held that they had souls and intellects with which they cognized. All authors agreed that physical influences emanated from them on the material sublunar world: These heavenly influences were usually construed as the deity’s instruments through which He exercises His Providence over the sublunar world, including humankind. The fact that this lower world was not a chaos but followed some order was thus seen as due to the wholesome influences of the celestial bodies. The latter, however, were not taken to act on their own, but rather as God’s instruments.

The medieval study of the heavenly bodies straddled at least four disciplines: astronomy, natural philosophy, metaphysics, and astrology (including medical astrology), each of which reasoned from its own premises and problématiques. Medieval thinkers stood, as it were, at the crossroads of all these disciplinary traditions, and integrated the information they provided into their views of the cosmos.