The chapter sketches a broad picture of some ideas, antecedent to Aristotle’s work, about the origin and development of living beings. Against the background of the new cosmological and metaphysical framework of Aristotle’s biological enterprise, it emphasizes what distinguishes Aristotle from the Presocratics and Plato: his rejection of a shared causal story that would account for both the origin of the universe and the birth of animals and plants. This shift helps to make intelligible Aristotle’s rejection of hylozoism and of the opposite view that life arises, mysteriously, from inanimate material ingredients. To demonstrate that Aristotle discusses the biological views of his predecessors without directly using them to build his own theory, the chapter first turns to Presocratic fragments, mostly of Anaximander and Empedocles, which connect biological matters and cosmogony. Second, the chapter takes a fresh look at how Plato reshapes this connection in his Timaeus, offering a new account of the nature of the universe and the nature of human beings. This account then enables us to evaluate, in the chapter’s final section, the changes that Aristotle brings to the study of living beings, including his rejection of the notion of the latter’s progressive formation.

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.

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.