Debate
Thomas Aquinas and Siger of Brabant: One Intellect for All?
1270–1277 · Does each human being think with an intellect of their own, or is there, as Averroes read Aristotle, a single intellect for all – and may a philosopher follow an argument to conclusions that contradict the faith?
In the 1260s some masters of the arts faculty in Paris, above all Siger of Brabant, read Aristotle’s On the Soul with the commentary of Averroes: the intellect that grasps universal truths is one and separate for all human beings and joined to each person only in the act of thinking. If so, there seemed to be no personal immortality and no individual merit. Bonaventure warned against such teachings in sermons from 1267; in 1270 Thomas Aquinas answered with On the Unity of the Intellect against the Averroists. On 10 December 1270 the Bishop of Paris, Étienne Tempier, condemned thirteen propositions, the first of them that there is one intellect for all; on 7 March 1277 he condemned 219. The dispute still raises the question of how free philosophy can be within a community of faith.
Positions
Aristotle, read with Averroes
In his Questions on the Third Book of On the Soul (late 1260s) Siger argued that the intellect is separate and eternal and united with the body only in its operation, while the form of the body is the sensitive soul. Under the pressure of Thomas’s arguments he revised this view. In On the Intellective Soul (early 1270s) he declared that, proceeding as a philosopher, he was asking what the philosophers had meant rather than what is true; he admitted that he had long been in doubt both about what natural reason should hold here and about what Aristotle had thought, and concluded that in such doubt one must hold to the faith, which surpasses all human reason.
Held by
- Siger of Brabantc. 1240–1284
This human being thinks
Thomas fought the Averroists with the philosophers’ own arguments, not, he said, with the teachings of the faith. Reading Aristotle with his Greek and Arabic commentators, he denied that the single intellect was Aristotle’s doctrine and called Averroes less a Peripatetic than a corrupter of Peripatetic philosophy. His central argument starts from experience: “this individual man thinks” (hic homo singularis intelligit). If the intellect were a separate substance merely linked to our images, the person would think no more than a wall sees when its colour is seen. The intellect must therefore be a power of the soul, which is the form of each human body. Thomas ended by challenging his opponents to answer in writing instead of speaking in corners before boys.
Held by
- Thomas Aquinasc. 1225–1274
The bishop’s verdict – and what it meant
Bonaventure had warned in his Paris sermons of 1267–73 against masters who taught the eternity of the world and one intellect for all. Tempier’s prologue of 1277 accused some masters of holding things true according to philosophy but not according to the Catholic faith, “as if there were two contrary truths”; historians now agree that no medieval author held such a “double truth”. Siger was summoned before the inquisitor of France in 1276 and died at Orvieto in the early 1280s; Dante placed him in paradise beside Thomas. Pierre Duhem saw in 1277 the birth of modern science; no historian of science now accepts this in full, and whether the condemnation also targeted Thomas is still debated (John Wippel against Roland Hissette).
Held by
- Bonaventurec. 1221–1274
Read more
- Hans Thijssen: Condemnation of 1277 (Stanford Encyclopedia of Philosophy)
- Dag Nikolaus Hasse: Influence of Arabic and Islamic Philosophy on the Latin West (Stanford Encyclopedia of Philosophy)
- Sten Ebbesen: Boethius of Dacia (Stanford Encyclopedia of Philosophy)
- Thomas Aquinas: De unitate intellectus contra Averroistas, Latin text (Corpus Thomisticum)
As of 10/2026. Summaries for orientation – the sources give the full arguments. · How Agora is made