Aquinas’s theology, as presented in his Scriptum, is “scientific” in the Aristotelian sense of this term. Some of its arguments for conclusions are based on theology’s “proper” principles—the articles of faith—but many others are purely rational demonstrations. As the basis for his rational arguments in theology, and in particular his treatment of the divine essence in d. 8, he introduces philosophical principles, and offers dialectical arguments for them, which are thoroughly Avicennian. In order to understand Aquinas’s commentary on d. 8, (...) then, it is not just helpful but necessary to see how he makes use of doctrines coming from the Metaphysics of Avicenna’s Book of Healing. So we look first at Aquinas’s source texts in Avicenna, and then at how he makes use of them in his commentary on the Sentences, Bk. 1, d. 8. (shrink)