2. - Albert the Great (d. 1280), Summa theologiae, book I, treatise 3, q. 15, chap. 2, a. 2, c. 1:

Summary

In this text, Albert deals with Augustine’s theory of the image of the Trinity. An examination of this theory leads him to an investigation of the relation between the soul and its powers. Albert contends that the soul and its powers are distinct. He maintains that the soul’s powers are propria, that is, necessary accidents, and following Avicenna he claims that they “flow” from the essence of the soul. In this text, Albert also considers the identity theory, on which the soul and its powers are the same entity but rejects it because it “borders on heresy”. He argues that the identification of the soul and its powers is perilously close to the identification of essence and power in God. Finally, Albert invokes the Boethian notion of a “power-whole” (totum potentiale) to develop his own account of the soul and its powers and to make sense of the Augustinian claim that our rational soul is an image of the Trinity. Albert was one of the main defenders of the distinction theory in the second half of the thirteenth century, and his version of this theory influenced Aquinas.