In this text, Durand rejects a common assumption undergirding much of the Latin medieval debate about the relation between the soul and its powers. According to this assumption, which we can call the uniformity assumption, all powers of the soul that bring forth vital operations, such as the intellect and sight, bear the same relation to the soul. Identity theorists maintained that all of these powers are identical to the soul, while distinction theorists held that all of these powers are distinct from the soul. Against this consensus, Durand argues that some powers of the soul are identical to the soul, while others are distinct from it. More precisely, he advocates an identity theory with respect to the vegetative powers but a distinction theory with regard to the sensory and rational powers. He motivates his identity view regarding the vegetative powers with the argument that these powers have substances as their effects and the premise that causes must be like their effects. To motivate his distinction theory regarding the sensory and rational powers, Durand does not draw on Aquinas’ Category Argument, which he thinks is unsound.

Chapter 10 studies theories of demonic obstinacy, the state in which the fallen angels or demons are unable to avoid sinning and have a limited ability to do good. The external cause of obstinacy is God’s refusal to offer them the grace of repentance and of justification. Beginning with Aquinas, theologians searched in addition for an internal, psychological cause of their obstinacy – a great challenge, given their shared belief that the angels’ will is by nature oriented to the good. Aquinas traces their obstinacy to the fixity of their cognition, and Henry of Ghent to the forcefulness of their will. Certain Franciscan thinkers explain the demons’ obstinacy by means of a divine intervention, binding their will to evil (Olivi), causing their immoderate self-love (Scotus), causing in them a habit of wickedness (Auriol), or even causing in them hatred of God (Ockham). Durand of St. Pourçain returns to the standard account prior to Aquinas, which explains the demons’ obstinacy by a divine decision, with no reference to their psychological condition. In addition to the cause of obstinacy, theologians discussed whether the demons, though necessarily obstinate, are nevertheless free.

Chapter 5 concerns the free will debate in the early fourteenth century. It thoroughly discusses the Franciscans Duns Scotus and William of Ockham, who make a sharp distinction between will and nature, that is, between a free power or cause that controls its act and one whose act is determined by external circumstances. Scotus and Ockham make the will more independent from a cognized good than previous thinkers. Using unedited texts, the chapter also presents what may well be the strongest statement of intellectualism at the time, by John of Pouilly, who builds on Godfrey of Fontaines to explain why, although our choices are moved by the cognized object, we control our choices. More briefly, the Dominicans Hervaeus Natalis and Durand of St. Pourçain are considered, whose general approach resembles Pouilly’s. As a thinker developing an intermediary theory, the chapter studies Peter Auriol, according to whom the will controls directly which judgment considered during deliberation becomes the final judgment that causes one’s choice. The dividing issue among these thinkers is, at bottom, whether the will controls its acts directly or only by means of deliberation.