Summary Peter of Ireland (Petrus de Ybernia) was born sometime around the beginning of the thirteenth century in Ireland, probably of a Norman family. He probably left Ireland aged around age 15 to pursue his studies abroad. His interest in medical and scientific questions would suggest a stay at Oxford, whereas his approach to logic would suggest a Parisian influence. By the middle of the century he was Professor of Logic and Natural Philosophy at the University at Naples. Peter is perhaps one of the best known of medieval Irish thinkers on the continent owing to the fact that he was held to be the teacher of the young Thomas Aquinas at Naples University from 1239-44. As such, it would be he who, in all likelihood, first introduced Thomas to the study of Aristotle and perhaps also to the commentaries of Avicenna and Averroes. The works presented here date from at least a decade later, and relate to lectures given at Naples in the 1250s and 1260s. The extent to which he was held in respect by his contemporaries is to be seen in his solution (determinatio) to the disputed question on the origin of the design of an animal's body which was held before King Manfred around 1260. It was, perhaps the culmination of a famous scholarly career. TABLE OF CONTENTS Preface Introduction Life, Longevity and Death Peter of Ireland, Life and Works The De longitudine commentary The Determinatio Magistralis Principles of the Edition and Translation Text and Translation Bibliography Indices