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.