Christianity

A series of Christian authors during the first centuries C.E., later known as "the Fathers," defended the faith to contemporary philosophers. Roman imperial religion was syncretistic. Apart from the Christians only the Jews refused to mingle their God with the gods of the pagans. Christians claimed that Jesus of Nazareth was the Son of God and had promised to send the Holy Spirit, or Paraclete, into the world to be "with" his people. Contemporary philosophy described a Trinity in descending order: a Supreme Being, a Logos, a "Soul of the World." Christians insisted that the three "Persons" in one God in their Trinity were equal and coeternal. There were long-running debates about the manner in which God could have "become man." The definitive creed of the council of the whole church held at Nicaea in 325 provided an "official" statement of the approved faith.

With the fall of the Roman Empire, the arena of debate changed. In the Eastern, Greek-speaking half of the old Roman Empire, Christian learning survived in deeply conservative monasteries and focused on a mystical spirituality colored by late Platonism. Christian thought and learning in the West moved into the new Christian monasteries, the cathedral schools, and eventually, from the end of the twelfth century, into the newly created universities. Islamic scholarship had preserved and developed Greek thought and was absorbed in its turn by the Christian scholars of the thirteenth century.

Thinkers of the Middle Ages such as Peter Lombard (c. 1095–1160) and Thomas Aquinas (c. 1224–1274) worked out a "systematic theology" covering the existence and nature of God, Unity, and Trinity; the way in which God became man and why; a doctrine of the church and the sacraments; and the relationship of human free will to the foreknowledge and predestination and grace of an omniscient and omnipotent God. For most of fifteen hundred years in the West the church dominated intellectual endeavor to the point where philosophy and science were subsumed in theology.