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Boundaries of Science: Medieval Condemnations of Philosophy as Heresy

Background: Controversy and History

Condemnation and Censorship. In 1277, the Bishop of Paris, Etienne Tempier, condemned 219 philosophical principles, prohibiting anyone at the University of Paris from teaching these ideas on pain of excommunication. Just over a week later, the Archbishop of Canterbury, Robert Kilwardby, issued a separate list of principles, banning their teaching at the University of Oxford. These events mark a climax in the 13th-century controversy over Aristotelian natural philosophy and the scientific revolution it triggered. 

Aristotle’s books on natural philosophy, such as Physics and On the Soul, had been translated into Latin in the 12th century, and were gradually absorbed into Latin scholastic thinking in the early 13th century. At the start of the century, the University of Paris banned the books altogether. The books, however, contained a coherent and valuable science which the Latin scholastics were eager to study. Over the course of the century, censorship of books gave way to assignment of their reading, and condemnations instead focused on specific ideas found in them.

Eternity of the World. What was the issue? Aristotle’s natural philosophy covered a range of topics which today we would classify as ‘science’. His Physics, for example, offered explanations of how time, matter and motion can be understood. This science presented a coherent and convincing system of how the world worked. It came to be adopted as the science of the late Middle Ages, yet it contained ideas which were unacceptable to a Christian society. One of the most controversial ideas to come out of Aristotle’s books was his theory of the Eternity of the World. He gave persuasive arguments for the world’s eternity in Physics, based on principles of time, matter and motion which he developed earlier in the book. To a Christian audience, this theory contradicted Creation as revealed in Genesis.

Unicity of the Intellect. The other major issue was over the theory of the Unicity of the Intellect. This theory was developed by the great Muslim philosopher Averroes (d. 1198) of Cordova, Spain. He wrote commentaries on Aristotle’s books which were read throughout the Arab world, and were translated into Latin in the early 13th century. His analysis helped explain complicated ideas in Aristotle, and went further. In On the Soul, Aristotle had offered an explanation of how the human intellect works, accounting for how we learn new ideas. However, the description was brief, leaving many questions unanswered. Philosophers after him, such as al-Farabi, Avicenna and Averroes, would build on his explanation, aiming to be consistent with what he had taught but filling out the description. The version Latin scholastics reacted to in the late 13th century was that of Averroes. Averroes posited a single intellect shared by all human beings, and for the duration of a lifetime only. To Christian (as well as Muslim) readers, the theory denied the afterlife of individual souls, their judgment by God as good or bad, and their destination in heaven or hell.

Heresy. Both the Eternity of the World and the Unicity of the Intellect were censured in the Paris Condemnations of 1277. One might think that these two theories, which contradicted such fundamental Christian beliefs as Creation and Salvation, were heretical. They were certainly against Christian faith, and the Condemnations banned them on pain of excommunication. Yet strictly speaking, these theories were not heretical. An idea became officially heretical when it was declared so by a pope or general Church council. They alone had authority throughout the Catholic world. A bishop’s authority covered only his diocese; so the Condemnations in Paris applied only to that city. Furthermore, excommunication, the punishment threatened in 1277, did not necessarily involve heresy. People could be excommunicated without having committed heresy. So, technically speaking, the ideas were not heretical.

Nevertheless, a number of scholastics of the late 13th and early 14th centuries called the controversial theories ‘heretical’ in their philosophical and theological works. The scholastics were generally quite precise in their word use, and restricted their vocabulary to accurate terms, in strictly constructed sentences. Their writing style was not far different from that of scientific reports today. They were well aware of what constituted heresy – many of them were theologians. For this reason, their term use is significant.

Interestingly, the philosophers and theologians employing the term ‘heresy’ were not always writers resistant to the new thinking or fierce defenders of Christian doctrine against philosophy. In fact, we find scholastics representing a range of positions applying the label to the controversial theories. While some were relatively ‘conservative’ writers, such as Bonaventure and Henry of Ghent, others who used the term were more open to the possibilities of philosophy, such as Thomas Aquinas and Giles of Rome. More surprisingly, we find examples of this term use by what some historians have called ‘Radical Aristotelians’ (who supported theories contradicting Christianity), such as Siger of Brabant and Boethius of Dacia. In some cases, the writers promoted the very theory they labelled ‘heretical’. Giles of Rome and Siger of Brabant did this when they abandoned theories they had previously supported, acquiescing to censure or pressure. Aquinas and Boethius of Dacia used the word ‘heresy’, frequently and pointedly, while putting forward highly controversial positions. Evidently strategies were involved in this term use.

Taken together, these and other examples found through the project’s research trigger a question: What were these diverse thinkers doing? What motivations lay behind their calling the controversial theories ‘heretical’? These are the questions guiding the project, whose aim is to answer them by looking at the philosophical context of the labelling, and the personal and career circumstances of the writers using the term.