In this text, Ockham deals with whether memory, intellect, and will are really distinct powers. He answers in the negative. After presenting first Aquinas’, then Henry of Ghent’s, and finally John Duns Scotus’ views in some detail, along with replies, Ockham presents his own uncompromising identity theory of the powers of the soul. Based on the principle of parsimony, he argues that the rational soul is identical to the intellect and the will. By transitivity, this entails that the intellect is identical to the will so that the rational soul is a single power to engage in acts of thinking and and willing. Fleshing out his view, Ockham also gives a sort of rule for knowing when distinct cognitive and appetitive powers must be posited, and when not. According to this rule, if everything outside of a cognizer or desirer remains the same, and the cognizer or desirer is able to have an act of one power, while being unable to have the act of another power, then those powers must be distinct. For example, some people may be unable to see while being able to hear and other people may be unable to hear while being able to see. It follows that sight and hearing must be distinct powers.

The introduction describes the scholastic Latin debate over the relation between the soul and its powers in the late thirteenth and early fourteenth century. It shows that this debate concerned the question of how a living being’s natural kind, which is determined by its soul, and its kind-specific powers are related. Is a living being’s soul the very same thing as its kind-specific powers, or is its soul perhaps something more basic upon which its kind-specific powers depend? The introduction shows that there were two overarching answers to this question in the thirteenth and fourteenth century: the identity theory, according to which the soul and its powers are identical, and the distinction theory, according to which the soul is distinct from its powers. The introduction first highlights that the debate between identity and distinction theorists already arose in the twelfth century in response to Augustine’s doctrine of the image of the Trinity. It then traces, in broad strokes, the development of the debate from the twelfth century until 1250. Finally, it discusses the phase between 1250 and 1320 focusing on the reception of Aristotle’s theory of the soul in the Latin West.

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.