The years following Abelard's entry into St.-Denis were enormously productive. Not only did he return to teaching dialectic, but he started to examine one of the most difficult questions presented by Christian doctrine, namely, how one can say that God, the supreme good, is simultaneously Father, Son, and Holy Spirit, without implying that each divine person can be identified with the other two. Thirty years earlier, Roscelin of Compiègne had concluded that even though God was one, “Father” and “Son” had to be described as words signifying separate things (res). In the eyes of St. Anselm and his admirers, Roscelin had fallen into the heresy of tritheism. Abelard felt that he could provide a more elegant explanation, based on rational argument, rather than simply on the authority of Scripture or of the Fathers of the Church. The specific doctrinal issue raised by Roscelin created a possibility for him to develop a broader argument about the relationship between classical philosophy and JudaeoChristian teaching about God.
In the Historia calamitatum, Abelard insists that he was driven to find analogies acceptable to human reason to elucidate the divine unity and trinity by his students, who were demanding “human and philosophical reasons” for Christian belief.1 Abelard's explanation glides over the complex web of rivalries and debates with his teachers that prompted its original composition over a decade earlier. In a letter to the bishop of Paris, written around 1120, Abelard claims that he wrote the treatise principally to refute Roscelin's argument that the three persons of the