For the modern reader, Timaeus 35a counts among the more abstruse passages in Plato’s dialogues. For ancient Platonists, too, it was considered to be obscure, yet also exerted an enduring fascination because it was believed to contain the key to understanding Plato’s concept of the soul. It provides a technical description of the composition and nature of the world soul and can therefore be used better to understand the (rational) human soul, which was held to be structured analogously. Plutarch of Chaeronea is the author of an exegetical work dedicated to this passage. Even though it is the oldest extensive treatment to have come down to us, there is strong evidence, as I hope to show, for an older exegetical tradition, going back to debates in the early Academy. This exegetical tradition may not have been continuous, but there are traces of it even in the Hellenistic era. In this essay I offer a reconstruction of the tradition preceding Plutarch.

Johansen examines the role of internal heat in the theories of nutrition and animal generation in Plato’s Timaeus. There, Plato does not ascribe the status of being besouled to all beings which engage in nutrition, but to beings with perceptive faculties. This raises questions as to the status of nutrition in the explanation of life and besouled beings.

The chapter presents an investigation into the Presocratic background of soul theories, more specifically, the relationship between fire and soul in Empedocles. Trépanier argues that Empedocles fragment B 9 does not give us a positive account of fire as soul, but targets a rival Presocratic account of fire as soul.

Thein provides a detailed analysis of Aristotle’s analogy between “the phusis in the pneuma” and “the element of the stars” in Aristotle’s GA (736b29–737a7). With the help of several passages in GA which discuss the role of pneuma in the generation of living beings, as well as passages of De caelo, where the first body is presented as an animate, self-moving but soulless entity, Thein makes the case that the key to the analogy lies in the shared link between motion and animation, a link which, in these two cases only, does not require the actual presence of the soul.

Betegh explores to what extent the Presocratic philosophers made the motive power of heat topical, and how they tried to provide an explanation of that power. He argues that while the motive power of heat never seems to obtain a principal role in the cosmological theories of the Presocratics, it appears to take a more important role in the explanation of living beings in a number of theories.

Reece discusses Diogenes of Apollonia’s claim that “all existing things are differentiated from the same thing and are the same thing” (DK 64B2, Simp. Phys. 151.31–32), namely air. He examines Diogenes’ principle that causal interaction and change require some sort of uniformity among the relata, and considers the questions which this principle raises.

Gelber focuses on passages in GA where Aristotle treats heat and cold as agents which are said to be making (poiei), fabricating (dêmiourgei), solidifying (pêgnutai), putting together (sunistatai), or working (ergazetai) to accomplish something, and thereby playing a role in the formation of a living organism. Gelber s aim is to explain how heat and cold do this, and the significance, for Aristotle, of calling heat and cold the tools of soul in his explanation of animal reproduction.

Macfarlane highlights Aristotle’s use of the concept of pathological pneuma, which reveals Aristotle’s connections with the medical ideas current in his time. Macfarlane’s analysis casts new light on this connection, the difference between respired and connate pneuma, and on the relation between connate pneuma and blood.

Popa focuses on the role of the two basic active dunameis, the hot and the cold, in Aristotle, Meteorology IV. There, the dispositional properties of the homoeomers are often defined and explained in virtue of bodies’ reactions to heat and cold: some homogeneous bodies are solidifiable by heat, others by cold. Popa argues that Meteor. IV aims to account for the coming about and persistence of uniform stuffs by appealing to what he calls “thermic equilibrium” (summetria, logos). The main purpose of this chapter is to clarify the ways in which Aristotle puts this notion to work in his study of homogeneous materials (especially in Meteor. IV) and, through this clarification, to contribute to a better understanding of the role played by proper or internal natural heat in his scientific works.