This is the first great commentary in the Western European tradition of expounding Aristotle's On the Soul. Dated about 1235, this work by Richard Rufus of Cornwall is a major contribution to the history of Western philosophy and the study of Aristotle. Indeed, no future account of thirteenth century philosophical psychology will be able to ignore the contribution of Richard Rufus. Following Aristotle, Rufus addresses questions as diverse as "how do we reproduce and grow", "how do we see and hear", "how do we understand ourselves", and "how is our immortal soul united with our body?" Its exposition and its questions date from about 35 years before Thomas Aquinas wrote his commentary on On the Soul, so its publication will prompt a re-evaluation of Aquinas's theory of the soul. As the copious notes to this edition indicate, not only is this the earliest surviving commentary on Aristotle's On the Soul taught at a Western University, but it was read by most of Rufus's early successors. Part of this commentary was published in 1952 but this present edition benefits from two recently discovered complete manuscripts. In addition to the text itself, this edition features an extensive introduction which presents the reader with the subsequent tradition, both published and unpublished. Abbreviations Introduction Sententia cum quaestionibus in libros De anima Liber I Liber II Liber III Indices Jennifer Ottman earned her B.A. at Amherst College and a Ph.D. at Yale University. She has been associated with the Richard Rufus Project since 1999 and has served as associate editor since 2011. She is also a collaborating editor and translator for the Greystones Manuscript Project, which began work in 2011 on the theological writings of the early-fourteenth- century English Benedictine Robert Greystones; a volume which was published in 2017. After graduating from Reed College, Rega Wood got her Ph.D. from Cornell University. Since 1976, she has prepared critical editions of major works of medieval philosophy and theology, including works by Richard Rufus, John Duns Scotus, William Ockham, and Adam Wodeham. In 1984, she discovered previously unknown works by Richard Rufus of Cornwall and, since 2000, she has been the principal investigator of the Richard Rufus Project (RRP). RRP is funded by the National Endowment for the Humanities and Indiana University, and also supported by Stanford University (rrp.stanford.edu). She has taught at St. Bonaventure University, Yale University, Stanford University, and Indiana University, Bloomington. After studying philosophy as an undergraduate in Australia, Neil Lewis obtained his PhD degree at Pittsburgh in the United States, developing an interest in medieval philosophy. His research has focused on Robert Grosseteste and early thirteenth-century English philosophy. He is a core member of the Richard Rufus of Cornwall Project, which is devoted to the preparation of critical editions of the works of Richard Rufus of Cornwall, and a core member of the Ordered University Project devoted to interdisciplinary study of Grosseteste's scientific works. Most of his academic career has been spent as a professor in the philosophy department at Georgetown University in Washington D.C. Christopher Martin's undergraduate and graduate degrees both came from Sussex University in the UK and his PhD from Princeton in mediaeval philosophy. After studying at Princeton, he taught at the State University of New York at Stony Brook until 1987 and then moved to the University of Auckland in New Zealand. His research covers the whole range of ancient and mediaeval philosophy but concentrates on the history of logic and in particular logic from the 12th to the 14th century. He has published many papers in this field and has held visiting positions at Cambridge University, The Ecole Practique des Hautes Etudes in Paris, and at the Scuola Normale in Pisa.