Thomas Aquinas was a prolific writer. His most extensive work is Summa Theologica, which he probably wrote between 1265 and 1272 but left unfinished. This imposing set of tomes, which comprises thousands of pages of tightly reasoned responses to an astonishing range of questions about church theology and doctrine, is not only the crown jewel of Scholasticism, that is, of medieval theology and philosophy, but one of the crown jewels of Western culture. His Summa contra Gentiles is remarkable as an attempt to demonstrate to nonbelievers the reasonableness of the Christian faith. In addition to these two most famous works, Aquinas also wrote commentaries on numerous treatises by Aristotle; various Bible commentaries; records of theological and philosophical disputes; and sundry treatises, letters, and notes. This prodigious output is especially impressive because Aquinas achieved it all within the span of about twenty years.

The Dominance of the Roman Catholic Church in Society and Education

Aquinas lived during an age when the Roman Catholic Church was the overwhelmingly dominant wielder of political and religious power in most of Europe. The Protestant Reformation, which established a rival alternative to the Catholic Church, was still some 250 years off when Aquinas was alive. Church and state were not separated and, in fact, were largely identical. There were no European nations in the modern sense of fully sovereign countries that determine their own economic, political, and social agendas.

Clerics, who were usually the only people who could read and write, possessed a monopoly on the world of learning. Education was necessarily Catholic learning and took place almost exclusively in monasteries. Very few universities existed, and most of these were institutions for the training of future clerics. For six years, candidates for a bachelor’s degree studied the seven liberal arts: geometry, grammar, logic, rhetoric, astronomy, music theory, and arithmetic. After completing this course of study, students could continue studying law, medicine, or theology for up to another twelve years in pursuit of a master’s degree or doctorate degree. Theology was the most difficult and prestigious field.

The Disputatio

One of the distinctive features of universities in Aquinas’s day was the so-called scholastic method, which was embodied in the disputatio. The disputatio was a public debate among scholars on a particular topic or question and took place according to a strict procedural format. First, a teacher posed a previously announced question to an advanced student. This student then took a position with respect to the topic in question. Other teachers and students subsequently countered the advanced student’s responses with objections, which the advanced student then attempted to rebut. On a day soon afterward, the teacher summarized the various arguments for and against the debated question and rendered his own decision in the determinatio. This culture of spirited public debate led to the development of refined techniques of argumentation and rhetoric. Trained in this arena of intellectual jousting, Aquinas proved himself to be one of its foremost practitioners. The structure and topics of the Summa Theologica and the Summa Theologica contra Gentiles are derived directly from this tradition, and both works are essentially transcripts of debates conducted according to the rigid rules of the disputatio.

Influences of Plato and Aristotle

Aquinas’s greatest influence on intellectual history was his shifting attention from the works of Plato to those of Aristotle. Much of the history of Western philosophy involves the elaboration and development of ideas that are either explicit or implicit in the writings of these two great ancient Greek philosophers. Plato was particularly influential among thinkers in the church’s early history, and St. Augustine (354–430 CE), one of the church Fathers, derived many of his views from Plato’s writings. Plato had maintained that an unbridgeable divide separates the transient, illusory, material world that we perceive with our senses and the changeless, eternal world of transcendent reality. For Plato, the realm of eternal and perfect Forms is the only proper object of study, containing as it does the only true reality. St. Augustine saw Plato’s philosophy as profoundly congenial to Christianity in that Plato’s concept of two worlds, one eternally perfect and the other inherently imperfect, mirrors Christianity’s own postulation of two worlds, earthly and divine.

In contract, Aristotle had drifted into obscurity, if not outright oblivion, as far as the church was concerned, and it is thanks only to the efforts of Jewish and Arabic scholars that his writings survived at all until Aquinas came along. Thus, the teachings of Plato reigned supreme in church orthodoxy when Aquinas was studying. Aquinas bucked this tradition, recovering Aristotle for the West and virtually single-handedly assimilating him into Catholic orthodoxy.

The Influence of Aquinas’s Works

Aquinas’s views are of more than merely philosophical interest, as they are official Catholic doctrine and thus represent a living set of traditions and beliefs. The Roman Catholic Church is one of the world’s most ancient, enduring, and powerful institutions, spanning nearly two thousand years and claiming some one billion adherents all over the globe. In 1879, Pope Leo XIII declared Aquinas’s teachings to be official church doctrine, cementing Aquinas’s status as one of the most influential philosophers and theologians ever.

The question of whether Aquinas’s writings represent the achievement of human reason or the products of divine inspiration has been the subject of fierce debate, and one’s answer to that question is likely to depend on whether one accepts church teachings in the first place. Within the church, it is safe to say that Aquinas’s significance is inescapable.