Aquinas–Siger on Latin Averroism
Faith and reason, or the doctrine of double truth
Venue: Aquinas, *De Unitate Intellectus contra Averroistas* (1270); Siger's commentaries; Tempier's Paris condemnations of 1270 and 1277.
The defining medieval confrontation between Aristotelian philosophy and Christian theology.
In 1270s Paris, Siger of Brabant taught a thoroughgoing Aristotelianism — drawing especially on Averroes's commentaries — that included the doctrines of the eternity of the world and the unity of the agent intellect (one intellect shared among all humans). These positions conflicted with Christian doctrines of creation in time and individual immortality. Aquinas's *De Unitate Intellectus* (1270) refuted the unity of intellect on philosophical grounds, arguing that individual intellectual souls are required even within Aristotelian principles. Bishop Tempier condemned 13 propositions in 1270 and 219 in 1277 — some directed at Aquinas's own positions. The controversy raised the question: can Christian theology accept Aristotelian natural philosophy in toto, or must it modify or reject parts? Aquinas's synthesis became the official Catholic response, but Siger's "Latin Averroism" continued underground.
Historical Context
The recovery of Aristotle's full corpus, via Arabic translations and commentaries, transformed 13th-century Latin philosophy. Universities struggled to incorporate the new material while preserving theological orthodoxy. The condemnations of 1277 marked a temporary defeat for unbounded Aristotelianism.
Parties
Aristotelian philosophy and Christian revelation do not conflict at the level of truth — but they are not equally complete sources. Where philosophy seems to teach what revelation denies, philosophy has misread itself; a corrected Aristotelianism is fully compatible with Christian doctrine.
Key arguments
- Unity of intellect refuted: individual intellectual souls are required even on Aristotelian principles (each human cognises distinct content).
- Eternity of the world cannot be proved by reason; Christian doctrine of creation in time is compatible with all that philosophy can demonstrate.
- Faith and reason both come from God; genuine philosophy cannot conflict with genuine revelation.
- Reading Aristotle in light of Christian commitments yields a coherent synthesis.
Allied schools
Philosophy, faithfully expounded, teaches certain propositions (eternity of the world, unity of intellect) that conflict with Christian revelation. The two domains have different methods; reason genuinely teaches what theology must hold otherwise.
Key arguments
- Aristotle's arguments for the eternity of the world are demonstrative.
- The unity of the agent intellect best explains how individual humans participate in universal cognition.
- Philosophy as a discipline must follow its own arguments wherever they lead; deference to revelation is the proper attitude of faith, not of philosophy.
- The two domains can each be honoured without forcing harmonisation.
Dimensions Engaged
Observer
Observer · Number: is there one intellect or many?
Matter
Bears on Matter · Conservation and Ontological Status through doctrines of creation.
Time
Time · Extent: is the world eternal or created in time?
Verdict in retrospect
Aquinas's synthesis won, both intellectually and institutionally: the Thomistic position became the normative Catholic philosophy (declared as such by Leo XIII in 1879). Siger's "double truth" (a label historians dispute the accuracy of) has been read as an early form of the philosophy/theology demarcation that modernity would institutionalise differently. The condemnations of 1277 had the long-term effect of opening space for non-Aristotelian science, paradoxically preparing the late-medieval intellectual ground for early modern natural philosophy.
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Further reading
- Aquinas, *De Unitate Intellectus contra Averroistas* (1270; tr. Zedler)
- Pasnau, *Theories of Cognition in the Later Middle Ages* (1997)
- Bianchi, *Censure et liberté intellectuelle à l'Université de Paris* (1999)