The Iranian philosopher Ibn Sina (980 – 1037) — known to the Latins as Avicenna — had a large impact on Latin medieval thought. He was also an important medical authority up through the Renaissance. In terms specifically of the relation between philosophy and religion, the spirit of Ibn Sina’s work was a conciliatory one, in that way a bit like the emphasis of Aquinas on one truth. In terms of debates in the Latin world, he was most often cited by people in the broadly Augustinian as opposed to Aristotelian stream, but Albert the Great and Thomas Aquinas also used some of his formulations.
Ibn Sina was original in many ways. He recounts that he improved on Aristotle by putting God at the beginning instead of the end (See First Principles Come Last; God and the Soul). He also liked to talk about Being, which seems to have caught the attention of Aquinas and Duns Scotus (see Being, Existence; Ontology). Along with Augustine, he largely anticipates the “I think, therefore I am” of Descartes. Many Augustinians found agreeable resonances in things he said about what I am here calling subjectivity (see Augustinian Interiority). None of this seems particularly like a recommendation to me. Where Averroes criticized Avicenna from a more purely Aristotelian point of view (as he often did), I think the arguments of Averroes generally seem much more sound.
The Latin translations of Avicenna’s works introduced the Latin term for representation into philosophical discourse. Early antecedents of modern mentalism can be found in Augustine, and to some extent even further back in Plotinus, but Avicenna contributed significantly to its crystallization. He introduced the terminology of intentionality, as well as a pregnant distinction between “first” and “second” intentions. First intentions were a kind of immediate mental objects, while second intentions applied to thoughts about the first. Here, I believe, is the historical source of the two-stage theory of representation that Brandom has been concerned to criticize. Descartes and Locke picked it up from the Latin scholastics.
The German philosopher Ernst Bloch wrote an intriguing — but I think misguided — little book called Avicenna und die Aristotelische Linke (1952). By analogy with the historical category of “Left Hegelianism”, he wanted to develop a concept of “Left Aristotelianism” in the Latin middle ages. His selection of Avicenna as its main representative is quite perplexing in view of the way citations to Avicenna most often figured in Latin disputation, where they were most often used to support what seem to me like more conservative, “Augustinian” positions in opposition to more Aristotelian positions. Bloch does quote some interesting passages about the concept of matter. To me, these seem possibly related to the notion of multiple substantial forms, which was one of the biggest points of contention between Augustinians and Latin Aristotelians.
(Albert the Great and Aquinas wanted to strongly insist that each thing has a single substantial form. What makes this difficult to evaluate is that the specific notion of “substantial” form is a much later — and much narrower and more univocal — invention not clearly apparent in Aristotle’s own works. So, the single-substantial-form thesis cannot be Aristotle’s own, and I don’t feel a need to defend it, even though I usually strongly favor the Aristotelian side in Augustinian-versus-Aristotelian disputes. Consequently, even though (as I understand it) one of the main motivations for the multiple-substantial-forms thesis was to support a very non-Aristotelian dualism of soul and body and I don’t like that motivation, the idea itself of multiple forms does not seem inherently bad. It might be understood as a sort of reification of the different senses or meanings of “form” in Aristotle.)