Chapter 2 explores how Franciscan theologians understood the similarities and differences between animals and humans. The Summa Halensis most frequently stressed clear difference and a strong boundary. Similarities were recognized, however, especially in relation to the corporeal. The Summa was not consistent in its approach to these similarities: sometimes they were simply natural features posing no moral or intellectual challenges, whereas on other occasions they were dangerously deceptive and symbolic of human sin. Bonaventure also accepted that in many respects the bodies of humans and animals were the same. Beyond this, however, he was not struck by much in the way of similarity. He took it for granted that humans were the most perfect animals, unique amongst animals in their possession of reason. Made in the image of God, humans related to God very differently from animals. Animals served humans, answering to their bodily and even emotional needs. Bearing symbolic meaning, they were God’s tools. Bonaventure did not see any of the similarities that underpinned more complex understandings in the work of others. For Bonaventure, the boundary between humans and animals was always clear-cut.

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.

Chapter 1 demonstrates that in his De legibus William of Auvergne emphasised the differences between animals and humans, regarding them chiefly as tools. God used them to shape human behaviour, both by demanding sacrifice and by granting them symbolic meaning. Demons used them in natural magic. Humans used them as valuable and sometimes necessary property in pursuit of survival, and to ensure proper relations with God. In the De universo, however, William noted significant similarities between animals and humans. Some animals knew and thought in very similar ways to humans. The power of their wills was similar to that of humans. These similarities were most likely to receive attention when William discussed providence or when he analysed animals in order to work out the nature of higher beings on the grounds that if something of lower standing in the hierarchy of being had a power or quality, beings higher up must also possess that same power or quality, though to a greater degree and perhaps with other powers in addition. This last approach meant that William treated animals as a profoundly valuable learning resource, one predicated on the existence of meaningful similarities across the boundaries that structured the hierarchy.