THE SCHOOLMEN period in Oxford during exile from Paris in 1303 The text previously known as the Opus Oxoniense is now seen as consisting of elements from an ongoing revision of this course, which continued throughout the Paris years The Reportata Parisiensia bears testimony to a late stage of the revision from the hands of students attending the lectures The deWnitive form of a medieval lecture course was attained when the lecturer compared his own drafts with his students’ notes, and incorporated the material into a single, approved, text known as an Ordinatio The publication of the Ordinatio— never Wnally retouched by Scotus himself—has been the major task of the Scotist Commission Between 1950 and 2001 seven volumes of this critical edition appeared, completing the commentary on Sentences I–II For Ordinatio III and IV scholars still rely on the last two books of the Opus Oxoniense as printed by Wadding The Vatican editions of the Lectura and Ordinatio are the main point of reference for the study of Scotus by present-day philosophers and theologians But two works of uncontested authenticity provide evidence of Scotus’ mature thought The quodlibetical questions undoubtedly belong to the brief period when Scotus was regent master in Paris, in 1306 or 1307 The brief monograph De Primo Principio, published in several editions since 1941, belongs to the last period of his life, and some scholars believe that it was written in Cologne in the year of his death Finally, the genuineness of a work entitled Theoremata is still the object of scholarly dispute The balance of opinion now seems in favour of authenticity, but if the work is genuine it testiWes to a remarkable volte-face by Scotus on an important topic, the question whether God’s existence can be proved by the natural light of reason Scotus is not an easy author to read His language is crabbed, technical, and unaccommodating, and the structure of his arguments is often diYcult to discern He had, however, one of the sharpest minds ever to have engaged in philosophy, and he well deserved his sobriquet ‘the subtle doctor’ In his brief academic career he altered the direction of philosophical thinking in many areas and set it on new courses to be followed for centuries On many major issues Scotus took the opposite side to Aquinas In his own mind, if not in the light of history, equal importance attached to his disagreements with another of his seniors, Henry of Ghent Henry taught at Paris from 1276 to 1292 and defended many of the ideas of Augustinian Neoplatonism against the radical Aristotelianism of some of the arts 85