Boundaries of Science: Medieval Condemnations of Philosophy as Heresy

Ann Giletti, Marie Curie Fellow, explains her research


What do you do when a scientific idea is strongly convincing, but conflicts with a fundamental religious belief you cherish?  How can you hold two contradictory ideas?  Can both be true?  Religion and science have a long history of both shared topics and clashes.  My project looks at a controversy in the late Middle Ages to see how conflicting scientific and religious ideas were handled, and where a boundary was drawn to exclude scientific ideas from Christian society.  Not everyone agreed where that boundary should be.

The controversy was over Aristotelian natural philosophy (what we would call ‘science’), where certain theories were incompatible with Christian beliefs.  These issues, previously discussed by Muslim and Jewish philosophers in Spain and the Muslim world, came in the thirteenth century to the attention of Christian philosophers and theologians at the universities.  One example is the theory of the Eternity of the World, which Aristotle proved convincingly in Physics. The theory was at odds with the doctrine of Creation.  Another theory, the Unicity of the Intellect, was developed by Cordovan Muslim philosopher Averroes (d. 1198), based on his reading of Aristotle’s On the Soul. He argued that there was one intellect shared by all humanity, with individuals borrowing a portion of it only for their lifetime.  This theory denied the afterlife of individual souls in heaven or hell.  In the 1270s in Paris and Oxford, university teaching of many such philosophical theories was banned, and several academics were examined for errors against faith.

One might think that these controversial theories were heretical, given their denial of Christian beliefs and the university condemnations.  Yet heresy had a precise definition in the Middle Ages.  To be heretical, an idea had to have been condemned by a pope or general Church council.  Only they had authority throughout the Catholic world.  There was no such decree during this controversy.  Curiously, university scholars knew the definition of heresy, yet some called the theories ‘heretical’ in their philosophical and theological writings.  Odder still, thinkers with diverse philosophical views – variously rejecting or embracing dangerous theories – used the term.  These include prominent figures, such as Thomas Aquinas, Bonaventure, Henry of Ghent, Giles of Rome, Siger of Brabant and Boethius of Dacia.  My research is into what motivated them to call theories ‘heretical’ – in some cases when they were in fact embracing ideas they seemed to denounce.  Did some think the ideas should be heretical?  Did others use the term for protection while exploring dangerous philosophical conclusions?  Clearly strategies and diverse motivations were involved, and my work is to understand what they were and how they reveal medieval negotiation of the relationship between faith and reason.

This research is for a Marie Curie project, funded by the European Commission’s Horizon 2020 programme.  Its results will be published in articles and a book with the provisional title Boundaries of Science:  Medieval Condemnations of Philosophy as Heresy.