He was born in Poitiers, and completed his first studies there. He was then educated at Chartres under Bernard of Chartres, where he learned the differences between Aristotle and Plato and later at Laon under Anselm of Laon and Ralph of Laon, where he studied biblical scriptures. After his education, he returned to Poitiers, where its believed he taught. He then returned to Chartres to teach logic and theology and took over Chancellor after Bernard from 1126-1140. It is in Paris where we also know he gave lectures. From a passage from the text, Dialogue with Ratius and Everard, by the Cistercian Everardus, we learn that Gilbert was more popular in Paris than in Chartres. Everardus writes that he was fourth to attend Gilberts lectures in Chartres and three hundredth to attend in Paris. In Paris, John of Salisbury attended Gilbert's lectures in 1141 and was greatly influenced by them. John of Salisbury would later become chancellor of Chartres and also wrote over Gilbert saying: He taught grammar and theology, would whip a student who made a grammatical error, if he believed a student was wasting time in class he would suggest they take up bread making, and last when he lectured he used philosophers, orators and as well as poets to help interpret. Sometime in the 1140s, Gilbert published his Commentary on Boethius's, Opuscula Sacra. Although intended as an explanation of what Boethius meant, it interpreted the Holy Trinity in such a way that it went against the teachings of the church. In 1142, Gilbert became Bishop of Poitiers, and within the same year two archdeacons, Arnaud and Calon, denounced Gilbert for his ideas on the Trinity. It was also in 1142 when Gilbert's teaching position was taken over in Chartres. By 1147, in Paris, Peter Lombard attacked Gilbert for his trinitarian beliefs. In 1148, Saint Bernard of Clairvaux, known as the great detector of heresies, brought Gilbert to trial. Saint Bernard had previous reasons to believe Gilbert was a heretic because when Abelard was tried and condemned, the school of Chartres--where Gilbert was chancellor at that moment—backed Abelard. Pope Eugene III presided over the trial. During the trial, Gilbert and Bernard were asked to recite and speak of specific biblical scriptures. Bernard, being nowhere near as well versed as Gilbert, was not able to condemn him. It was decided however that in order to make the church happy, Gilbert had to change parts of his book that were not in accordance with the official position on faith. Gilbert died in 1154.
Gilbert is almost the only logician of the 12th century who is quoted by the greater scholastics of the succeeding age. The Liber sex principiorum, attributed to him, but of an anonymous author, was regarded with a reverence almost equal to that paid to Aristotle, and furnished matter for numerous commentators, amongst them Albertus Magnus. Owing to the fame of this work, he is mentioned by Dante as the Magister sex principiorum. The treatise itself is a discussion of the Aristotelian categories, specially of the six subordinate modes. The author distinguishes in the ten categories two classes, one essential, the other derivative. Essential or inhering in the objects themselves are only substance, quantity, quality and relation in the stricter sense of that term. The remaining six, when, where, action, passion, position and habit, are relative and subordinate. This suggestion has some interest, but is of no great value, either in logic or in the theory of knowledge. More important in the history of scholasticism are the theological consequences to which Gilbert's realism led him. In the commentary on the treatise De Trinitate of Boethius he proceeds from the metaphysical notion that pure or abstract being is prior in nature to that which is. This pure being is God, and must be distinguished from the triune God as known to us. God is incomprehensible, and the categories cannot be applied to determine his existence. In God there is no distinction or difference, whereas in all substances or things there is duality, arising from the element of matter. Between pure being and substances stand the ideas or forms, which subsist, though they are not substances. These forms, when materialized, are called formae substantiales or formae nativae; they are the essences of things, and in themselves have no relation to the accidents of things. Things are temporal, the ideas perpetual, God eternal. The pure form of existence, that by which God is God, must be distinguished from the three persons who are God by participation in this form. The form or essence is one, the persons or substances three. This distinction clearly goes against the church's tenet of divine simplicity. It was this distinction between Deitas or Divinitas and Deus that led to the condemnation of Gilbert's doctrine.
