This chapter highlights the close interconnection between cosmology and human nature in the Timaeus. According to Timaeus, human beings are not merely part of the cosmos; they play a crucial role in explaining how the cosmos came to be. The cosmos must contain three kinds of mortal beings in order to be complete, and all three derive from human beings, as a result of varying degrees of moral and cognitive failure. Recognizing the distinctive role human beings play in completing the cosmos complicates the standard picture of Timaeus’ cosmology, as well as his account of human nature. While in large part the cosmos is a product of divine craft, in some part it is the product of the inevitable disturbance of immortal souls due to mortal embodiment. Human beings have a special status as the first generation of mortal beings, as well as the only ones produced solely by divine craft. However, this distinction does not extend beyond the first generation, nor does it include any women. Ultimately, Timaeus’ account of human nature blurs the lines between humans and gods, as well as between humans and non-human animals.

This chapter sets out to explore the thesis that Plato, at least in his later years, in his efforts to identify the nature of his First Principle, was inclined to settle on the concept of a rational World Soul, with demiurgic functions, and that this was a doctrine that his faithful amanuensis in his last years, Philip of Opus, advanced on his own account, in the belief that in this he was developing the latest theories of his Master.

The chapter explores how the Stoics account for the totality of movement in the cosmos – in other words, the agency of the world. The Stoics take the world to be a complex and divine living-being. Their physics combines what today we might call physics, biology and theology. The Stoics put forward two premises that appear to be in tension. First, they claim that the active principle is the sole source of movement and cause of everything. Second, they offer a scala naturae according to which kinds of entities differ by the way in which they move and jointly co-cause all movement in the world. This One-Many Problem is the Stoic version of what is later called the problem of free will and determinism, or so I argue. As the Stoics conceive of the problem, the challenge consists in showing how both premises – One Cause and Many Causes – are true. The Stoic approach strikes me as attractive, both because it looks at humans together with animals and other parts of the world and because of its upshot for human agency. Our reasoning, including our decision-making, constitutes some of the causes that co-cause the world’s overall movements. What remains puzzling, however, is that our reasoning is subject to norms. Ultimately, I argue, the puzzle is how norms for practical reasoning fit into the physical world. This reconstruction does justice to the evidence. It recognizes that the Stoics address human movement in the context of a scala naturae. And it predicts what indeed we find: a wide range of texts about the status of human assent, indicative of the awareness that this is not an easy topic.

In his commentary on Nicomachus’ Introduction to Arithmetic, John Philoponus explains the role that mathematics, and hence harmonics, play in Platonic philosophy, as redefined by the Neoplatonists. There are two main issues regarding harmonics. The first issue: harmonics is one of the mathematical sciences that lead to the knowledge of divine and absolutely immaterial entities; but harmonics also concerns other mathematical disciplines, because there is an astronomical harmony, that is, the harmony of the revolution of the stars, and there is a geometric harmony, that is, the cube, one of the Platonic solids that are the constitutive elements of the physical world as a geometric model of equality. The second issue: there exists a harmonic proportion, already known to the Pythagoreans, Plato and Aristotle. Both these aspects in Philoponus’ study of harmonics have a common denominator, namely the fact that, as Plato teaches in the Timaeus, the universe, its soul and human souls have a numerical structure based on the relationship between two principles, that is, equality and inequality. But harmonics is precisely the mathematical science of relationship. Therefore, harmonics has a privileged place in the Neoplatonic philosophical system, as Philoponus’ commentary worthily testifies.

This part of Chapter 2 offers two definitions of ‘cosmos’ and then describes the latter as a whole containing the largest stable structures composed of the five elements: aether, fire, air, water and earth. It explains the division of the cosmos into the upper or supralunary part, which is made of aether and where things are incorruptible and in regular circular motion, and the lower or sublunary part, where things are diverse and less regular, composed of the remaining four elements, and subject to constant generation and corruption. The perfect supralunary part forms a system of concentric rotating spheres. While the fixed stars all move ‘on one visible surface of the whole of the heavens’, where they keep their position, the planets are simply said to each move in their own orbit, with no explicit mention of the higher number of moving spheres posited by Eudoxus or Callippus. Below the lowest planetary sphere, that of the Moon, the sublunary part of the cosmos begins. It is also organised in concentric spheres, each one dominated by one of the four elements, starting with fire and ending with earth in the immobile centre of the universe. The author pays special attention to the immutable aether that belongs to the causal chain extending from God to all the motions in the earthly region of the universe. In virtue of its physical perfection, the ether is indispensable for God’s guidance and administration of all heaven and Earth.

Chapter 5 of De mundo is markedly different from the preceding chapters examining technical details of astronomy, geography and meteorology. Chapter 5 takes an overall survey, presenting a view of the whole cosmos as a unified, well-ordered, magnificent and eternal whole – a true kosmos. Chapter 5 can be divided into three parts: the first introduces the Heraclitean principle of the harmony of opposites (396a33–b22), the second shows how this principle applies to the cosmos (396b23–397a5), and the third argues that the cosmos, built on this principle, is majestic and indestructible (397a5–b8). The detailed analysis of each part is accompanied with an attempt to position this text against the views of other Hellenistic philosophical schools, of the Epicureans and the Stoics as well as the Platonists. Having set forth the Aristotelian doctrine of the eternity of the cosmos, it was important for the author of De mundo to show that this does not undermine the beauty and teleological order of the world nor does it remove the need for God, thus setting the stage for Chapter 6.

The third chapter focuses on the Iranian doctor Abū Bakr al-Rāzī (sometimes called the 'Arab Galen'), who was attacked by later Islamicate thinkers for his disciplinary overreach, and his bid to replace Galenism with his more theologically informed system of medicine and philosophy. In particular, it argues that al-Rāzī seeks to weaken the epistemic authority of Galenism through his critiques of Galen’s explanations of certain ideas from Plato’s Timaeus. I first consider the Middle Platonic and Neoplatonic sources on which al-Rāzī may have drawn to elaborate his 'anti-Platonism' – his Platonism in response to Galen's Platonism. Turning finally to the Doubts about Galen, I demonstrate that al-Rāzī attacks Galen on the subjects of creation, pleasure, and the soul for neglecting God's role in the cosmos in his interpretations of the Timaeus. In reformulating the boundaries of medicine to include theological knowledge, which belonged in ancient epistemological schemes to metaphysics, al-Rāzī, I conclude, promotes the doctor-metaphysician in opposition to Galen’s more limited philosopher-doctor as the most reliable investigator of the cosmos.

Galen attempts to define the Timaeus as a medical resource to justify medicine’s right to comment on issues regarding the soul and the nature of life, to which philosophers had long laid claim. I call attention to Galen’s commentary On the Medical Statements in Plato’s Timaeus and the Arabo-Latin prologue to the Synopsis of Plato’s Timaeus to illustrate how his assertions that the dialogue contains ‘medical’ information allow him to draw more expansive boundaries for medicine. My analyses of On the Doctrines of Hippocrates and Plato and The Faculties of the Soul Follow the Mixtures of the Body reveal that Galen advances more monopolistic claims on the soul for medicine by appealing to his anatomical expertise and the dialogue's link between bodily and psychic disease to show the pertinence of his medical expertise to psychological controversies and ethics. I conclude with a discussion of Galen's interpretation of the Timaeus' account of vegetative sensation, which posits a homology between plants and humans that he exploits to extend medicine's boundaries beyond the world of the body.

The cosmic eschatology of the Gospel of Mary is the subject of Chapter 4, and it primarily examines the opening dialogue between Jesus and the disciples. I argue that the cosmology of the Gospel of Mary is simpler and more christocentric than has been assumed by past exegetes. This gospel shares the common Christian belief that matter is the raw material of a cosmos shaped by God. Matter has been affected by passions, which in turn affect the individual causing sin and death. Jesus, here called ‘the Good’, has come to dissolve/restore the cosmos to its original constituent parts. The Gospel of Mary stands in contrast to the ‘traditional’ expectation of a future parousia as found in the synoptic gospels, and actively contradicts this expectation by stating that ‘the Son of Man is within’. The make-up and dissolution of the cosmos is interpreted by using ideas already present in John and Paul.

Although the Gospel of Mary is a dialogue gospel, the text’s narrative frame is just as integral to understanding the message of the gospel as the eschatological teachings in the dialogues. The narrative frame includes Jesus’ departure, Mary’s intervention, and the ensuing dispute among the disciples. This chapter explores possibilities for what was contained in the missing opening pages of the Gospel of Mary, firmly situating the text within the dialogue gospel genre. It then analyzes the Saviour’s farewell discourse, which encourages the disciples to be active participants in the Christian message of salvation. The section on Mary’s intervention focuses on her relationship with the male disciples and her relationship with Jesus, and argues that the Coptic manuscript heightens animosity between the disciples in contrast to the earlier Greek versions. Mary’s relationship to Jesus, on the other hand, is one of succession. The final part of the narrative frame sees the disciples split into two factions, with Mary and Levi on one side and Peter and Andrew on the other. It is unclear at the ending of the gospel whether the disciples are reconciled, and this is explored in light of other dialogue gospels such as the Pistis Sophia.

Chaucer lived in a society that was aware of childhood and adolescence as distinctive stages of human life and which inherited practices whereby young people were brought up and trained for adulthood. Informally, at home, children were introduced to social norms, religion and work. Those from wealthier families underwent more formal education, mastering literacy at home, in schools or in great households, where they learnt reading, rules of courtesy, French and, in the case of some boys, Latin. Chaucer’s works refer in passing to most of these processes, with particular attention to adolescents, including university scholars. During the fifteenth century his works in general came to be seen as having educational value. The Astrolabe, first written for his son Lewis, seems to have been used for teaching reading to other young children while his major writings were recommended as suitable literature for older ones.

Chaucer’s universe was an interconnected system, in which all things had their divinely ordered place. This chapter explores the sources and status of natural knowledge in the later Middle Ages, and Chaucer’s employment of that knowledge for poetic and didactic purposes. It explains how medieval philosophers used their inheritance of classical and Islamic knowledge, refining an understanding of a harmonious cosmos through the sciences of astronomy, cosmology, music and medicine. These were not just theoretical sciences, but practical arts. Chaucer understood, and explained, the astrological workings of tables and instruments and their predictive power for meteorology and medicine. He never let technicalities overwhelm poetry, but it is clear that the sciences were of great interest to Chaucer. They were worthy of serious study both for their practical potential and their philosophical or ethical implications, and a field in which, through his Treatise on the Astrolabe, Chaucer made his own unique contribution.