Thomism is the philosophical school that arose as a legacy of the work and thought of Saint Thomas Aquinas (1225–1274), philosopher, theologian, and Doctor of the Church. In philosophy, his disputed questions and commentaries on Aristotle are perhaps his most well-known works. In theology, his Summa Theologica is one of the most influential documents in medieval theology and continues to be the central point of reference for the philosophy and theology of the Catholic Church. In the encyclical Doctoris AngeliciPope Pius X cautioned that the teachings of the Church cannot be understood without the basic philosophical underpinnings of Thomas' major theses:

The Second Vatican Council described Thomas's system as the "Perennial Philosophy".

Thomistic philosophy

General

St. Thomas Aquinas believed that truth is to be accepted no matter where it is found. His doctrines draw from Greek, Roman, Jewish, and Muslim philosophers. Specifically, he was a realist (i.e., he, unlike the skeptics, believed that the world can be known as it is). He largely followed Aristotelian terminology and metaphysics, and wrote comprehensive commentaries on Aristotle, often affirming Aristotle's views with independent arguments. Thomas respectfully referred to Aristotle simply as "the Philosopher." He also adhered to some neoplatonic principles, for example that "it is absolutely true that there is first something which is essentially being and essentially good, which we call God, ... [and that] everything can be called good and a being, inasmuch as it participates in it by way of a certain assimilation..."