Some passages of the Summa have become particularly well-known and widely studied, such as the section on the five ways to demonstrate God’s existence (Part 1, Question 2). The Parts subdivide into Treatises, Questions, and Articles-reflecting Aquinas’ distinctive method of philosophical argument now known as Thomism or the Scholastic method: He states the case for the opposing position, then refutes the points one by one while expounding his own point of view, citing relevant authorities. The Second Part deals with man in greater depth, and the Third Part discusses Jesus Christ, who serves as mediator between God and man in Christian thought. The First Part addresses God, gradually working its way through God’s creation and the angels to man. Aquinas frequently cites the works of “The Philosopher” (Aristotle), as well as such authorities as the Arab philosopher Averroes and the Jewish rabbi and philosopher Moses Maimonides.

Although the Summa is a theological work, it is deeply grounded in philosophical concepts and arguments. Aquinas drew from Jewish, Islamic, and pagan Greek sources, as well as the Christian Bible and the Church Fathers to form his arguments for the relationship between reason and revelation. He sought to reconcile Christian teachings with the insights of classical Greek philosophers, especially Aristotle (384-322 B.C.), whom Western Europe was rediscovering during Aquinas’ lifetime. Aquinas’ central idea was that reason and faith, or reason and revelation, complement each other.

Aquinas summa theologica