Avicenna and Thomas Aquinas seem to generally interpret Aristotle in different ways, and I am trying to understand the differences. Specifically, what are the differences between Avicenna's view and Thomas Aquinas' on agent intellect?
Agent intellect is the faculty that mediates between concrete things and abstract concepts. Avicenna and Aquinas represented opposite positions on its nature, and we do not know which position is closer to the truth even today, although the issues are phrased very differently of course.
The notion of agent intellect goes back to Aristotle who distinguished active and passive aspect in the intellect, just as matter and cause are in reality. He was very vague on the nature of this intellect "by virtue of making all things" however. Most Greek and Islamic commentators interpreted Aristotle to mean something transcendent to the human soul, as opposed to "potential" or "possible" intellect of humans, which is part of it. Avicenna elaborated and clarified this transcendent interpretation: agent intellect is the lowest in the series of spiritual substances that rules the sublunar world and illuminates possible intellect with intelligible forms. As such, it is the source of abstract concepts and first principles of science. This dovetailed nicely with Augustinian illumination of the soul by God, and some Christian commentators even identified the agent intellect with God himself.
Aquinas rejected this transcendent interpretation altogether, and gave an elaborate theory of agent intellect as human soul's own power. In particular it is responsible for stripping sense perceptions of their "material" contents, turning them into universals and making them accessible to passive intellect. Although he had precursors in Bonaventura and Philip the Chancellor, in contrast their accounts like Aristotle's were quite obscure. Here is Aquinas in his own words:"I say together with Avicenna, that the possible intellect... is different in different individuals... But I add that also the agent intellect is different in different individuals... It is necessary to postulate a power, belonging to the intellect, to create actually thinkable objects by abstracting ideas from their material conditions. That is why we need to postulate an agent intellect".
See Nejeschleba's Thomas Aquinas and the Early Franciscan School on the Agent Intellect for more context.