When I wrote the blog post on Plato's school of thought, I mentioned Anselm and his ontological argument, but I forgot to note Peter Lombard's textbook: Four Books of Sentences. This was the chief theological textbook until the time of Thomas Aquinas. His support of the seven sacraments led to it being accepted as authoritative at the Council of Florence in 1439.
Plato's reality was completely in an unseen world. Aristotle insisted that universal have an objective existence but not apart from individuals things. They are a part of the objects and minds. He places more reality in the seen world rather than assuming that this life is only shadows.
Abelard was a major fan of Aristotle. He taught at the University of Paris. He believed that reality existed first in the mind of God, then in individuals and things. Plato's camp emphasized that they believe so that they may know. Abelard reversed that: I know in order that I may believe. He emphasized reasoning.
Downside: he did not believe that Christ's death satisfied God's wrath against sinners. He believe it simply compelled people to see Christ's love, their hearts to melt, and for them to come to God through moral influence. This is Pelagianism again, and it is not the Gospel taught in the Bible. His work Sic et Non, or Yes and No, was also a major textbook of the day.
Albertus Magnus was a brilliant man known mostly for his pupil who excelled him: Thomas Aquinas. Thomas, the Angelic Doctor, joined a monastery against his parents' wishes. Cairns describes him as large, shambling, taciturn, and somewhat absent-minded. He was the quintessential geek. His classmates called him a "dumb ox", and Albertus prophecied that the ox's lowing would fill the whole world.
R.C. Sproul loves Aquinas a lot more than I do. I like him much better thanks to Sproul, but Augustine is a far better theologian. He also believed reality exists first in the mind of God, then in people. His Summa Theologiae is the theology textbook to end all textbooks until the Reformation. He preached that man's will is bent by sin from the fall, but he did not believe it was completely determined to evil. Augustine taught that the human will was helplessly lost in evil. Aquinas is still a theologically sound man: he held orthodox views of the atonement, Christ's deity, life, death, and resurrection. He held sound Mariology. I look to the day where I can sit down and read his works.