Aristotle believed that the outermost stars are carried round us on a transparent sphere. There are directions in the universe and a preferred direction of rotation. The sun moon and planets are carried on different revolving spheres. The spheres and celestial bodies are composed of an everlasting fifth element, which has none of the ordinary contrary properties like heat and cold which could destroy it, but only the facility for uniform rotation. But this creates problems as to how the heavenly bodies create light, and, in the case of the sun, heat. The value of Simplicius' commentary on On the Heavens 2,1-9 lies both in its preservation of the lost comments of Alexander and in Simplicius' controversy with him. The two of them discuss not only the problem mentioned, but also whether soul and nature move the spheres as two distinct forces or as one. Alexander appears to have simplified Aristotle's system of 55 spheres down to seven, and some hints may be gleaned as to whether, simplifying further, he thinks there are seven ultimate movers, or only one.

This is the first English translation of Simplicius' responses to Philoponus' Against Aristotle on the Eternity of the World. The commentary is published in two volumes: Ian Mueller's previous book in the series, Simplicius: On Aristotle On the Heavens 1.2-3, and this book on 1.3-4. Philoponus, the Christian, had argued that Aristotle's arguments do not succeed. For all they show to the contrary, Christianity may be right that the heavens were brought into existence by the only divine being and one moment in time, and will cease to exist at some future moment. Simplicius upholds the pagan view that the heavens are eternal and divine, and argues that their eternity is shown by their astronomical movements coupled with certain principles of Aristotle. The English translation in this volume is accompanied by a detailed introduction, extensive commentary notes and a bibliography.

Aristotle argues in On the Heavens 1.5-7 that there can be no infinitely large body, and in 1.8-9 that there cannot be more than one physical world. As a corollary in 1.9, he infers that there is no place, vacuum or time beyond the outermost stars. As one argument in favour of a single world, he argues that his four elements: earth, air, fire and water, have only one natural destination apiece. Moreover they accelerate as they approach it and acceleration cannot be unlimited. However, the Neoplatonist Simplicius, who wrote the commentary in the sixth century AD (here translated into English), tells us that this whole world view was to be rejected by Strato, the third head of Aristotle's school. At the same time, he tells us the different theories of acceleration in Greek philosophy.

In chapter 1 of On the Heavens Aristotle defines body, and then notoriously ruptures dynamics by introducing a fifth element, beyond Plato's four, to explain the rotation of the heavens, which, like nearly all Greeks, Aristotle took to be real, not apparent. Even a member of his school, Xenarchus, we are told, rejected his fifth element. The Neoplatonist Simplicius seeks to harmonise Plato and Aristotle. Plato, he says, thought that the heavens were composed of all four elements but with the purest kind of fire, namely light, predominating. That Plato would not mind this being called a fifth element is shown by his associating with the heavens the fifth of the five convex regular solids recognised by geometry. Simplicius follows Aristotle's view that one of the lower elements, fire, also rotates, as shown by the behaviour of comets. But such motion, though natural for the fifth elements, is super-natural for fire. Simplicius reveals that the Aristotelian Alexander of Aphrodisias recognised the need to supplement Aristotle and account for the annual approach and retreat of planets by means of Ptolemy's epicycles or eccentrics. Aristotle's philosopher-god is turned by Simplicius, following his teacher Ammonius, into a creator-god, like Plato's. But the creation is beginningless, as shown by the argument that, if you try to imagine a time when it began, you cannot answer the question, 'Why not sooner?' In explaining the creation, Simplicius follows the Neoplatonist expansion of Aristotle's four 'causes' to six. The final result gives us a cosmology very considerably removed from Aristotle's.

In the three chapters of On the Heavens dealt with in this volume, Aristotle argues that the universe is ungenerated and indestructible. In Simplicius' commentary, translated here, we see a battle royal between the Neoplatonist Simplicius and the Aristotelian Alexander, whose lost commentary on Aristotle's On the Heavens Simplicius partly preserves. Simplicius' rival, the Christian Philoponus, had conducted a parallel battle in his Against Proclus but had taken the side of Alexander against Proclus and other Platonists, arguing that Plato's Timaeus gives a beginning to the universe. Simplicius takes the Platonist side, denying that Plato intended a beginning. The origin to which Plato refers is, according to Simplicius, not a temporal origin, but the divine cause that produces the world without beginning.

Of Philoponus' commentary on the Meteorology only that on chapters 1-9 and 12 of the first book has been preserved. It is translated in this series in two volumes, the first covering chapters 1-3; the second (this volume) chapters 4-9 and 12. The subjects discussed here include the nature of fiery and light phenomena in the sky, the formation of comets, the Milky Way, the properties of moist exhalation, and the formation of hail. Philoponus pays special attention to the distinction between the apparent and the real among the sky phenomena; he criticises Aristotle's theory of the Milky Way as sublunary, and argues for its origin in the heavenly realm; gives a detailed exposition of Aristotelian theory of antiperistasis, mutual replacement of the hot and the cold, as the mechanism of condensation and related processes. As in the first volume, Philoponus demonstrates scholarly erudition and familiarity with methods and results of post-Aristotelian Greek science. Despite the fragmented state of the work and the genre of commentary, the reader will find the elements of a coherent picture of the cosmos based on a radical re-thinking of Aristotelian meteorology and physics.

The subject of Aristotle's On the Heavens, Books 3-4, is the four elements of earth, air, fire and water, which exist below the heavens. Book 3, in chapters 1 to 7, frequently criticizes the Presocratic philosophers. Because of this, Simplicius' commentary is one of our main sources of quotations of the Presocratics. Ian Mueller's translation of this commentary gains added importance by enabling us to see the context which guided Simplicius' selection of Presocratic texts to quote. Simplicius also criticizes the lost commentary of the leading Aristotelian commentator, Alexander, and thereby gives us important information about that work. The English translation in this volume is accompanied by a detailed introduction, extensive commentary notes and a bibliography.