This book is about determinisism. It contains the two most important commentaries on the determinists' sea battle argument, and on other deterministic arguments besides. It includes the earliest full exposition of the Reaper argument for determinism, and a discussion of whether there can be changeless knowledge of the passage of time. It also contains the two fullest expositions of the idea that it is not truth, but only definite truth, that would imply determinism. Ammonius and Boethius both wrote commentaries on Aristotle's On Interpretation and on its ninth chapter, where Aristotle discusses the sea battle. Their comments are crucial, for Ammonius' commentary influenced the Islamic the Islamic Middle Ages, while that of Boethius was of equal importance to medieval Latin-speaking philosophers. It was once argued that Boethius was influenced by Ammonius, but these translations are published together in this volume to enable the reader to see clearly that this was not the case. Ammonius draws on the fourth- and fifth-century Neoplatonists lamblichus, Syrianus, and Proclus. He arranges his argument around three major deterministic arguments and is our main source for one of them, the Reaper argument, which has hitherto received insufficient attention. Boethius, on the other hand, draws on controversies from 300 years earlier between Stoics and Aristotelians as recorded by Alexander of Aphrodisias and Porphyry. This volume is essential reading for all those with an interest in the history of determinism. Ammonius' commentary on the first eight chapters of Aristotle's On Interpretation has appeared in a previously published volume in this series, translated by David Blank.