philosopher and teacher. A Breton by birth, he made his name as a teacher in Paris c.1125–41, becoming Chancellor of Chartres, probably in 1141. He took part in the examination of Gilbert de la Porrée at Reims in 1148.
Thierry's most original work was in the application of the liberal arts to Christian doctrine. His analysis of Boethius's Opuscula Sacra offered a more conservative interpretation of the Trinity than that proposed by Gilbert de la Porrée. For Thierry the doctrine of the Trinity might be deduced from a consideration of the unity (the Father), which leads to equality (the Son), and thence to the bond between the two (the Holy Spirit). The De Sex Dierum Operibus (On the Six Days of Creation) is a bold interpretation of Gen. 1 in the light of his study of Plato and Aristotle; he assigned the four Aristotelian causes to the Persons of the Trinity, the Father being the efficient cause, the Son the formal, and the Holy Spirit the final cause, whereas divinely created matter was the material cause.