Those whom modern scholars called Averroists were supposed to be unoriginal, dogmatic followers of Averroes. This turns out to be as inaccurate as the supposition that the Latin scholastics as a whole were unoriginal, dogmatic followers of Aristotle.
At issue here is what it is to be human, and in particular how the difficult Aristotelian concept of “intellect” relates to human beings. There were not just two but a wide variety of nuanced and well-argued positions on this.
Among the so-called Averroists, Siger of Brabant (1240-1280) is the best known name, but no full book has yet been devoted to his work. According to Alain de Libera, in his later works Siger developed original responses to Thomas Aquinas’ famous critique of Averroes.
Siger argued against Aquinas that the act of thought is not purely immanent but simultaneously immanent and transitive. That is to say, for Siger it is immanent in the human, but transitive in the separate intellect. While affirming a “separate” intellect, Siger emphasized against Aquinas that the total act of thinking is attributable to the whole human, and not just to the human’s intellective soul. Intellect is an “intrinsic operation” in the human that in a way does, and in a way does not, make it the “substantial form” and perfection of a material body. According to Siger, Aquinas’ claim that the intellective soul unequivocally is the substantial form of the body cannot be reconciled with Aquinas’ other claim that intellect as a power of the intellective soul is entirely independent of the body. Siger adopts Albert and Thomas’ term “intellective soul”, but for Siger only the animal and vegetative soul are united with the body in being. Intellective soul is naturally united with the body in operation but not in being, whereas Aquinas says they are united in being.
According to de Libera, Siger in his Questions on the Book of Causes argues that the form of the human is not simple, but is rather a composite comprising an intellect that “comes from outside” (in Aristotle’s phrase), and a vegetative and sensitive substance that is “educed from the power of matter” (de Libera, Archéologie du sujet vol. 3 part 1, p. 411, my translation). Intellect is said by Siger to be a “form subsistent in itself”. It is not a “substantial form” in the proper sense, which would imply that it was inherent in the human body. It is not in the body “as in a subject”. However, intellect has need of the human body (specifically, the phantasms of the imagination) as an object, and intellect is in turn attributable to the human as a whole, though it is not reducible to the biological organism. Intellect for Siger is neither the inherent form of the human nor a separate, external mover of the human, but a separate form with an operation that is intrinsic to the whole human, in which it participates by composition.
De Libera remarks in passing that the act of thought owes more to intelligible objects than to “intellect”. I would suggest that it is through language and culture and ethical practice that Aristotelian intellect “comes to us from outside”. We talking, encultured animals then acquire a spiritual essence that comes to be intrinsic to us, through our ethical practice, in which acquired intellect and animal imagination cooperate.
According to de Libera, for Siger “The ‘intelligent whole’ is composed of many psychic parts, which are not of the same nature, or of the same origin, or of the same ontological status” (p. 362).
Siger objects that Aquinas’ notion of intellect as united with the body in being “makes the act of thought a perfection of matter” (ibid). This makes the body intellect’s “subject of inherence”. But at the same time, applying Thomas’ own axiom that nothing is accomplished by a power separated from itself, Siger reproaches Thomas for being unable to account for “the integrality of the known” (p. 378), and specifically the knowledge of material things.
For Aquinas, establishing that there is an operation proper to the soul is essential to the possibility of the soul’s existence independent of the body, and thus to his philosophical argument for personal immortality. But Siger argues that in making intellect an operation proper (i.e., uniquely attributable) to the soul, Aquinas implicitly negates its attributability to the whole human. Intellection for Siger is “an operation common to the human composite as an integral whole” (p. 377). In other words, I think with my whole being, not just my “mind”.
De Libera concludes that Siger does preserve the possibility of personal immortality, which was a principal concern of Averroes’ critics. However, he finds that the texts do not support the claims of some recent scholars that Siger in his later works abandoned “Averroism” in favor of Thomism.
The phrase “form subsistent in itself”, according to de Libera, does not have the same meaning for Siger that it does for Thomas. Albert the Great had analyzed three logical possibilities for an “intermediate” kind of form that is neither fully separate nor inseparable from matter. According to de Libera, Siger’s work is consistent with this. Siger aimed at a mean between a Platonist excess of separation between form and matter, and what he perceived as a Thomist excess of union with respect to so-called substantial forms. De Libera does find, however, that Siger, like other authors, is too anxious to simplify the issues at stake, and that he goes too far in identifying the position of Aquinas with that of Alexander of Aphrodisias, who was regarded as having a “materialist” view of the human soul. He also says Siger goes too far in reducing Aquinas’ notion of form to the simple analogy of a stamp in wax.
De Libera meanwhile also raises doubts about Aquinas’ insistence on the absence of any intermediary between the intellective soul and the body. He notes that in a very different context, the Franciscan Augustinian Peter Olivi argued that the intellective soul is united with the body via the intermediary of the sensitive soul. Olivi’s position was rejected by the Council of Vienna in 1312.
De Libera accepts the notion of “substantial form” as genuinely Aristotelian, but appears to endorse the argument of Bernardo Carlos Bazán that Aquinas’ notion of intellective soul gives it a privileged ontological status that makes it more than a substantial form. According to Bazán, Aquinas’ anthropology from the very start goes beyond the Aristotelian hylomorphism that Thomas generally endorses. The form of a human in Aquinas — unlike anything in Aristotle — is such that it could not be the result of any natural generative process, but could only be created by God. Siger comes across as closer to Aristotle.
De Libera notes that in the wake of the English theologian Thomas Wylton (1288-1322), later so-called Averroists “invested massively” in a distinction between an inherent form and an assisting form, and regarded human intellect as an “assisting form”. (See also “This Human Understands”; “This Human”, Again; Averroes as Read by de Libera.)