The third chapter looks at the Western reception of Dionysius the Areopagite in the early Middle Ages and the channelling of thinking on theosis through Dionysius into the Western mystical tradition. This tradition is examined from Bernard and Bonaventure to the Rhineland mystics and Nicholas of Cusa, revealing a constant concern to integrate the intellectual ascent to the vision of God with experiential participation in the Word by faith.

This chapter examines the earliest natural rights theories in order to analyse philosophical connections between natural and human rights, concerning: scepticism, metaphysical dualism, and the authority of rights. First, the chapter studies Albert the Great’s principles of right and how he understood nature to be reason. Next, analysis of the main tenets of Henry of Ghent’s metaphysics, and his exposition of the soul’s property over one’s body, show that Neoplatonist dualism was fundamental in the development of the first natural rights theories. The philosophical solution to the poverty controversy, of human beings’ natural rights to use material goods, that Hervaeus Natalis proposed became the law of the Church when the Pope incorporate it in the bull, Cum inter nonnullos (1323). Hervaeus continued the metaphysical dualism of Henry and argued that natural rights endowed reality with normativity and hence authority. The chapter concludes by relating this intellectual history to contemporary rights theories. Natural and human rights are identified as a form of public reason that sometimes assists, other times substitutes for, individual right reason and judgement about morality.

The theology of Albert the Great (the teacher of Thomas Aquinas) remains understudied. Here Albert’s life and writings are introduced, with special attention to his theology of the Trinity, theology as science, union with God and the nature of happiness.

Chapter 2 examines the reception of Aristotle’s action theory from the 1220s to 1277 and its influence on novel theories of free will developed in this period. It shows that the reception of Aristotle led to a “psychological turn”: instead of assuming the existence of free will, theologians began to argue for it by clarifying the nature of intellect and will, in which free will is grounded. The chapter canvasses the theories of free will in broad strokes from William of Auxerre to Bonaventure, and in more detail regarding Thomas Aquinas and Siger of Brabant, whose views will provoke strong reactions. Following Aristotle closely, Aquinas understands choices as determined by the practical deliberation that precedes them; one chooses as one judges worth choosing, and one can choose otherwise only because deliberation allows one to judge otherwise. Appealing to the authority of Avicenna, Siger argues that what causes the will’s acts does so necessarily.

Chapter 7 examines medieval theories of the first cause of evil. Although Augustine denied that something good is the cause of evil, medieval thinkers routinely attributed to him the view that something good – the will understood as a power of the soul – causes something evil. The majority of the thinkers considered in this chapter use Aristotle’s notion of accidental causality to argue that the will can cause evil not per se – that is, not intending evil as evil – but incidentally. Nevertheless, if the will causes evil, they face the dilemma that a good will cannot cause evil at all, and an evil will cannot cause the first evil will. Medieval thinkers deal with this dilemma in different ways. For example, Bonaventure and others hold that the created will is naturally defectible, and hence not entirely unflawed, and so it can do evil. Aquinas argues that the will causing evil for the first time presupposes a momentary nonculpable deficiency, which becomes culpable at the moment of the evil choice. For Scotus, the will is so free that it can do evil even if it is unflawed. Although all these views trace evil to the will as its cause, they hold that evil is ultimately unexplainable.

Chapters 8–10 constitute Part III, entitled “Angelic Sin,” which raises the issue of how rational agents can do evil under ideal psychological conditions. Chapter 8 is about intellectualist accounts of angelic sin. Since according to these accounts, the will acts as the intellect judges best, evil acts presuppose some cognitive deficiency: either an outright error, or some occurrent nonconsideration that keeps the intellect from making the correct judgment. Thus one difficulty faced by intellectualist thinkers is how the cognitive deficiency can come about – especially since most thinkers here discussed assume that angels are infallible prior to making an evil choice. Another difficulty concerns control of the act. It is assumed that while the angels’ good or evil choice was up to them, the content of their knowledge was not up to them. Aquinas’s solution is that knowledge does not predetermine the use of that knowledge, which is up to the will. By contrast, Godfrey of Fontaines argues that the choice of the angels is caused by the cognized object; he fails to explain, however, how his theory avoids cognitive determinism.

Chapter 3 considers the work of two Dominicans, Albert the Great and Thomas Aquinas. Albert placed humans at the top of a hierarchy. He saw many similarities between animals and humans, the likeness diminishing with every step down the hierarchy. Although a hard boundary between humans and animals remained, it was just one of many that divided animals into categories, the pygmy from the human, the monkey from the pygmy, and so on. In the Summa theologiae Aquinas consistently stressed differences between humans and animals, but also noted significant similarities. Even if they could not grasp universals, for example, some animals could nevertheless think generally about types of other animal. Aquinas’s earlier work, the Summa contra gentiles, was especially imaginative in the way it explored the relationship between similarity and difference. Within the hierarchy of being, for example, he showed how difference might be generated by similarities in a variety of ways. Aquinas took an entirely different approach, however, when he set aside every aspect of the human which was in any way similar to the animal, concluding that contemplation of the truth was the sole feature that defined the human absolutely.