William’s course on the Logica vetus (Isagoge, Categories, Peri hermenieas, Liber VI Principiis) has been edited under the name of Giles of Rome. It is known in two manuscripts from Avignon (BM 1078 and BM 1089); there is a third manuscript (Vatican, Bibl Apost. Barberini, lat. 433) that is perhaps a copy of the ancient edition, and a fourth manuscript concerning the commentary on the Liber De six principiis (Berlin Staatsbibl. Preussischer Kulturbesitz, Fol.624, ff 51ra-62ra). The set of commentaries on Logica vetus is headed by a prologue called ‘‘principium’’ (Tabarroni 1988:374) or ‘‘divisio logice’’ (Gauthier 1989a:70*). This division is influenced by John of Dacia’s division of sciences (Tabarroni 1988:372). The attribution of the whole course to William can be based upon an ascription in one manuscript (Avignon 1089), but the most serious arguments are derived from the doctrinal content of the work, which is very close to the Lectura Tractatuum on Peter of Spain’s Tractatus, which is unquestionably by Arnaud. Quotations from Thomas Aquinas can be read in all parts of his work (Gauthier 1989a:71* for the Peri hermeneias’ commentary, as an example).
A. J. Gondras has given an edition ofWilliam Arnaud’s commentary of the Librum de six principiis though he does
Not attribute this work to him, but discuss in detail the attribution to Vital du Four. He sees the commentary as the work of a young Master because he does not quote the Fathers nor the theologians and also because he is far from being an expert in the Arts (Gondras 1975:187). The last point seems rather inaccurate considering the vast amount of quotations from Aristotle’s works on natural philosophy contained in the commentary, and the first one can probably be explained by the nature of the text commented upon and by the fact that the course belongs to the Arts Faculty, and not to theology. Gondras’ edition is based on two manuscripts from Avignon (BM 1078 and BM 1089), that is, from those manuscripts containing the whole course of William Arnaud on Logica vetus. Another version of the commentary on the Liber is mentioned in an other manuscript (Toulouse Arch. Dep. 4, F2, see Gauthier 1989a:71*, note 2).
One can gain an idea of William’s unpublished commentary on the Categories thanks to the study of R. Andrews (Andrews 2001:299-300) who listed his questions and published one on quantity, together with some similar questions written by other thirteenth-century masters (Andrews 2001:305-307). William follows Albert the Great’s solution with regard to the definition of quantity (Andrews 2001:284).
William’s commentary on the Peri hermeneias has been thoroughly examined by A. Tabarroni, elaborating on the discoveries of R. A. Gauthier (who mentions two other fragmentary manuscripts, Gauthier 1989a:71*). William is very faithful to Thomas Aquinas, whom he calls the ‘‘Expositor’’ not only in the sections where Aquinas’ Expositio is extant, but also in the final part of the treatise on which Thomas did not comment. This shows that William had access to an anonymous Continuatio otherwise partially transmitted in two manuscripts. His own exegesis is so dependent on his source that A. Tabarroni considers it a very good testimony for the reconstitution of that work (Tabarroni 1988:373-374). This anonymous Continuatio, strongly influenced by Herveus Natalis’ commentary on the Peri hermenias was thought to be authentic by William. A partial edition of the Continuatio is given by A. Tabarroni, followed by the parallel text of William (Tabarroni 1988:420-427).
William’s commentary on the Analytics is found in one manuscript (Barcelona, Arch de la Corona de Aragon Ripoll 109). It has been studied by R. A. Gauthier in his introduction to Thomas Aquinas’ Expositio: it is based upon Thomas but also upon Giles of Rome’s commentary on the same treatise, so that it should be dated after 1290 (Gauthier 1989b:65*-66*). A partial edition of his commentary on the Prior Analytics has been made by Grabmann (1928).