No very remarkable man arose with a rationalizing spirit, after Erigena, until Berengar of Tours in the eleventh century, who maintained that in the Sacrament the presence of the body of Christ involves no change in the nature and essence of the bread and wine. He was opposed by Lanfranc. But the doctrine of transubstantiation was too deeply grounded in the faith of Christendom to be easily shaken. Controversies seemed to centre around the doctrine of the real existence of ideas,--what are called "universals,"--which doctrine was generally accepted. The monks, in this matter, followed Saint Augustine, who was a realist, as were also the orthodox leaders of the Church generally from his time to that of Saint Bernard. It was a sequence of the belief in the doctrine of the Trinity. No one of mark opposed the Realism which had now become one of the accepted philosophical opinions of the age, until Roscelin, in the latter part of the eleventh century, denied that universals have a real existence. It was Plato's doctrine that universals have an independent existence apart from individual objects, and that they exist before the latter (_universalia_ ANTE _rem_,--the thought _before_ the thing); while Aristotle maintained that universals, though possessing a real existence, exist only in individual objects (_universalia_ IN _re_, --the thought _in_ the thing). Nominalism is the doctrine that individuals only have real existence (_universalia_ POST _rem_,--the thought _after_ the thing). It is not probable that this profound question about universals would have excited much interest among the intellectual monks of the eleventh century, had it not been applied to theological subjects, in which chiefly they were absorbed. Now Roscelin advanced the doctrine, that, if the three persons in the Trinity were one thing, it would follow that the Father and the Holy Ghost must have entered into the flesh together with the Son; and as he believed that only individuals exist in reality, it would follow that the three persons of the Godhead are three substances, in fact three Gods. Thus Nominalism logically led to an assault on the received doctrine of the Trinity--the central point in the theology of the Church. This was heresy. The foundations of Christian belief were attacked, and no one in that age was strong enough to come to the rescue but Anselm, then Abbot of Bec.