Just as Islamic philosophers reinterpreted faith by applying reason, subordinating revelation to reason, Western philosophers endeavored to incorporate the doctrines of Greek philosophy into the theology of the Christian church. Leaders in this movement included St. Augustine (Augustine of Hippo), St. Anselm, and St. Thomas Aquinas.

Augustine of Hippo (354–430) lived during a time when the last vestiges of the pagan world of the Romans was giving way to Christianity. His theological works, including sermons, books, and pastoral letters, reveal a Platonic influence, foreshadowing the movement of Scholasticism that emerged more than six centuries later (during the eleventh century). Augustine believed that understanding can lead one to faith and that faith can lead a person to understanding. He also argued that Christians can understand the nature of the Trinity by examining their own nature (through introspection).

One of Scholasticism’s founders, Anselm (c. 1033–1109) was a Benedictine monk who in 1093 became archbishop of Canterbury. He became famous for writing about the attributes of God (in his work Monologion) and for trying to prove the existence of God (in Proslogion) by rational means alone, arguing that God is that of which nothing greater can be thought; that of which nothing greater can be thought must include existence (if it did not, then something greater could be thought); and therefore God necessarily exists.

But the greatest figure of Scholasticism was St. Thomas Aquinas (1225–1274), who is also one of the principal saints of the Roman Catholic Church. In 1879 his philosophical works were declared the official Catholic doctrine by Pope Leo XIII (1810–1903). While he was teaching at universities in Cologne (Germany) and Paris between 1248 and 1272, Thomas Aquinas penned his major works, Summa contra gentiles (1259–64) and Summa theologica (1266–73). He discarded the Platonic leanings of St. Augustine (to whom truth was a matter of faith), interpreting Aristotle’s naturalistic philosophy: Similar to the Islamic philosopher Avennasar (c. 878–950), who argued that religion and philosophy are not in conflict with each other, Thomas Aquinas believed faith and reason are in harmony with each other. His work is considered the greatest achievement of medieval philosophy, making the thirteenth century Scholasticism’s golden age. Thomas Aquinas was canonized in 1323 and was proclaimed a doctor of the Catholic Church in 1567.