GILBERT of POITIERS (*Gilbertus Porretanus*). — Scholastic philosopher and theologian, born in Poitiers in 1076, died there in 1154. He studied at Chartres, where his teacher was Bernard of Chartres (not to be confused with Bernard Silvestris or of Tours, chancellor of Chartres in 1156), and later taught there and served as chancellor. He then taught in Paris, where Salisbury (v.). In 1142 he was appointed bishop of Poitiers.
Under the humanistic influence of Chartres, he commented on Boethius’s *Opuscula sacra*, or more precisely four of these treatises (PL 64). He prefaced them with a prologue, unpublished by Migne, partially edited by Hauréau and later in full by Grabmann (*Die Gesch. der scholast. Methode*, II, Freiburg in Br. 1912, pp. 417–19, note). While commenting on one of Boethius’s treatises, specifically *De Trinitate*, Gilbert encountered, right at the beginning of the first chapter, the words: “quare diversum etiam (as the identical) vel genere vel specie vel numero dicitur. *Sed numero differentiam accidentium varietas facit*.” Drawing on these words of Boethius, who in turn drew on Porphyry, Gilbert maintained that the universal is indeed in the individual but really distinct from the individuating principles (“accidentium varietas”), thus declaring himself in favor of a realism that was apparently moderate but in reality exaggerated. In keeping with this ultra-realism, Gilbert held that the three Persons of the Holy Trinity are not only really distinct from one another but also from the divine nature or essence (*Commentary on Boethius’s Second Opusculum*). This opinion was opposed by St. Bernard of Clairvaux and condemned in 1148 by the Council of Reims, in the presence of Pope Eugenius III; it was later repudiated by the author, who was compelled to acknowledge “neve Deus divina essentia diceretur ex sensu ablativi tantum sed etiam nominativi,” as one of his admirers, the historian Otto of Freising, wrote (*De gestis Friderici*, I.1, cap. 56, in MGH, *Scriptores*, XX).
Another work by Gilbert is the *Liber sex principiorum* (PL 188, 1257–70) on the last six Aristotelian categories not expressly treated by Aristotle; from it we see that Gilbert was among the first, around 1100, to introduce the “new logic,” namely the last books of the Aristotelian *Organon*, into the school of Chartres. The *Liber sex principiorum* earned, like a classical book, the honor of commentaries throughout the Middle Ages, alongside Aristotle’s works. Even St. Albert the Great commented on it, and Hermolaus Barbarus adapted its Latin for the Venetian edition of 1496, later reprinted in PL 188, 1257–70.
Gilbert had followers and opponents in both philosophy and theology. His influence was felt, directly or indirectly, even by Joachim of Fiore, who was condemned for similar errors regarding the Holy Trinity at the Fourth Lateran Council in 1215. Through the *Sententiae divinitatis*, which belong, if not to him, to his school, Gilbert also influenced Peter Lombard’s *Four Books of Sentences*. From St. Victor, and specifically from Walter of St. Victor, nearly a contemporary of Gilbert’s, came the *Contra quatuor labyrinthos Franciae*, which portrays Gilbert of Poitiers alongside Abelard, Peter of Poitiers, and even Peter Lombard as so many dissolvers of traditional thought.
Other works by Gilbert: Letter to the Abbot of Saint-Florent (PL 188, 1255–58); Letter to Bernard of Chartres (L. Merlet, *Lettres d’Yves de Chartres et d’autres personnages de son temps* [Bibliothèque de l’École des Chartres, 4th ser., 1], Paris 1855, p. 461); *Sermons on the Song of Songs* (Strasbourg 1497); Commentary on the Apocalypse (Paris 1512); Commentary on the Letters of St. Paul (unpublished; fragments in *Revue d’histoire eccl.*, 13 [1912], pp. 677–683, notes); Commentary on the Psalms (unpublished); *Sententiae divinitatis* (from Gilbert’s school). Besides these works, documents concerning Gilbert are found in various sources (Mansi, XXI, cols. 712–736); Otto of Freising, *De gestis Friderici*, I.1, cap. 56 (MGH, *Scriptores*, XX, p. 380 sqq.); Gaufridus, *Libellus contra Gillebertum* (PL 185, 595 sqq.); B. Geyer, *Die Sententiae Divinitatis*, together with Walter of St. Victor’s *Contra quatuor labyrinthos Franciae* (Münster 1909); John of Salisbury, *Metalogicon*, IV (ed. C. J. Webb, Oxford 1929); id., *Historia pontificalis* (MGH, *Scriptores*, XX, p. 524 sqq.).