St. Thomas of Aquino was born in the early 13th century to a high noble family that counted as its relatives two Holy Roman Emperors and the kings of Aragon, Castile, and France. Despite his heritage, St. Thomas chose the life of a teacher in the Dominican mendicant (begging) order instead of the high office planned by his family, whose members even detained him for more than a year to try to change his mind. (In later life he would also turn down an archbishopric to continue his teaching work.) Living in an age when political loyalties and cultural differences were transcended by a common Faith and language of scholarship, St. Thomas would work in France, Germany, and Italy until before his death around the age of 49.
The 13th century was, in many ways, the golden age of Scholasticism, the Christian intellectual movement that emerged with the Latin Renaissance of the 12th century and found its home in the universities of Western Christendom. It was characterized by its rigorous use of logic and dialectic to apply the Christian Faith, which led to the rise of many schools of theology, philosophy and law within the doctrinal framework of Catholic Christianity. In St. Thomas’ time, Latin thought had recently encountered the metaphysical and ethical writings of Aristotle, and in the ensuing debates with extreme Aristotelians and the anti-Aristotelians alike, St. Thomas would prove a formidable controversialist and speculative thinker. It is largely due to him that the Aristotelian corpus was purified of its errors and integrated into Catholic thought.
St. Thomas’ writings were marked by his openness to all the intellectual traditions known in his time. Thus his theological works contain, alongside copious reverent citations of Sacred Scripture, references to the Greek philosophical tradition (including its Roman, Jewish and Muslim interpreters); the theologies of the Church Fathers, especially St. Augustine (whose writings, like the Scriptures of St. Paul and St. John, were influenced to varying degrees by Greek philosophy); Roman law as revived by the Latin canonists; and the writings of earlier Scholastics, particularly St. Anselm and Peter Lombard. Using the dialectical method of Peter Abelard and the categories of Aristotelian logic, St. Thomas sifted these traditions for their valid insights, which he melded into a comprehensive Christian synthesis.
For St. Thomas was, above all, a Christian theologian, and so the integrating principles of his thought were founded on his devout Catholic Faith. He affirmed that God is the source of all truth, including what we know through philosophy (rational inquiry on God’s creation) and sacred doctrine (divine revelation, which reason receives through God-given faith). Of these two, sacred doctrine is nobler because it communicates the truths of salvation, which are beyond the reach of reason; and because, being God’s utterance, it gives greater certainty even on truths within reason’s grasp. In sum, St. Thomas was confident that philosophy rightly conducted cannot contradict sacred doctrine rightly understood, which completes and corrects it; and he sought to demonstrate the harmony of faith and reason throughout his work.
But while we need to believe in truth for our beatitude–since we cannot love God if we don’t know Him–it is charity (supernatural love of God) that unites us to Him. Because our capacity for love is limited by our nature and weakened by sin, God gave us His only-begotten Son Jesus Christ to be our Savior and Lord. By His Passion Christ redeemed us from sin, as His members in His mystical body the Church, and reconciled us with God; and by the grace we receive in the sacraments of His Church–which derive their power from the Passion of Christ–God elevates our nature that we might share His divine life and do His commandments. Thus are we able to supernaturally love God and our neighbor, and to see Him face to face in eternal beatitude. In short, as the synthesis of St. Thomas is founded on the unity of God’s truth, so it is consummated in the communion of His love.
The outline and method of St. Thomas’ thought can be clearly seen in his most famous work, called the Summa Theologica (Summation of Theology). Divided into parts, questions, and articles, its general structure begins with God and returns to Him (following the exitus-redditus schema of Christian Neoplatonism). As legions of students have seen from the much-anthologized article “Whether God exists?”, each article begins by stating the Objections to the correct conclusion. Then Aquinas cites an authority for his position (“On the contrary…”), followed by a reasoned argument for its correctness (“I answer that…). The article then concludes with Replies to the Objections. Each question and article builds on the conclusions of preceding questions, and article, making the Summa a theological edifice systematically built brick by brick from the best of Christian and non-Christian thought.
The impact of St. Thomas’ achievement in Catholic Christian thought cannot be over-stated. In the 16th century, his theology of grace (which united the moral emphasis of the Western Fathers and the mystical focus of the Eastern Fathers) was used by the Council of Trent to define the Catholic doctrine of salvation, and allowed the one true Church to steer clear of both Protestant dualism and Eastern Orthodox monism. In the late 19th and early 20th century, the Church used St. Thomas’ thought, especially his theory of knowledge, to resist the temptations to Fundamentalism and Modernism when confronted with modern philosophy. And amid the revival of Thomism in the Neoscholastic movement, it was on the basis of St. Thomas’ anthropology and ethics that the Church codified Christian Social Teaching, with which she responded to secular humanism and totalitarian ideology in the 20th century.
St. Thomas also exerted a pervasive influence on the secular world. In the Second Scholasticism of the Renaissance and Baroque periods, Catholics and Protestants alike debated and speculated in theology, philosophy, and law using the thought of St. Thomas; and they laid upon his foundations the beginnings of international law, natural rights discourse, modern economic theory, and (through Suarez and Descartes) modern Western philosophy. In the past decades many non-Catholics rediscovered Thomism even as Catholics increasingly adopted non-Thomist modes of inquiry. Various schools now claim his authority for their competing theories on economics, sexual ethics, and social organization; and Aquinas’ epistemology and anthropology were recently cited as a superior basis to explain cognition and other neurological phenomena.
In sum, St. Thomas Aquinas may well be one of the greatest systematic philosophers in history, alongside Aristotle, Shankara, and Immanuel Kant; and he is certainly, with St. Augustine and St. John Damascene, one of the greatest theologians in the Catholic tradition. Therefore, while the Church has ever valued and learned from a plurality of intellectual schools, various Popes beginning with Leo XIII have specifically encouraged the study of St. Thomas’ mind and method, as did the Second Vatican Council; and St. Thomas is honoured in the Church as her “Angelic Doctor” and “Common Doctor”. At the Council of Trent, his Summa was placed upon the altar beside the Sacred Scriptures and the decrees of the Popes; and the Constitution Dei Filius of the First Vatican Council is effectively a restatement of St. Thomas’ teaching on faith and reason, itself founded on the doctrine of Scripture and the tradition of the Fathers.
All this attention would likely have nonplussed St. Thomas himself: a man of deep faith and humility who, after a great mystical vision, declared that all he had written was straw. In the university, his soft-spoken manner and (apparently) bovine appearance reportedly caused his fellow students to call him the “dumb ox”. It was left to his teacher Saint Albert the Great–himself a renowned theologian and pioneer of natural science–to correct them with the eventual judgment of posterity: “You call him a dumb ox, but I tell you… his bellowings shall fill the world.” Thus it is as much for his holiness and humility as for his brilliance that St. Thomas is held up as an example to Christian thinkers. Thus Pope Leo XIII declared:
“let us follow the example of the Angelic Doctor, who never gave himself to reading or writing without first begging the blessing of God, who modestly confessed that whatever he knew he had acquired not so much by his own study and labor as by the divine gift”. (Aeterni Patris, 33)
See also our post “Free ebooks by and about St. Thomas Aquinas” (28 January 2013), Part I of which was re-published on this post; and our “List of eBooks in the Neoscholastic (“Manualist”) Tradition” (7 March 2013) listing links to texts influenced by Scholastic thought from the mid-19th century to the early 20th century. For other legally free ebooks, you may access the List of Free eBooks (Arranged by Title) and the List of Free eBooks (Grouped by Subject).
*The Introduction is drawn in part from the article “St. Thomas Aquinas” of the Catholic Encyclopedia. It is also based on various works I’ve read in the past, including Joseph De Torre, Introduction to Christian Philosophy; Etienne Gilson, Elements of Christian Philosophy and The Spirit of Thomism; Frederick Copleston, Medieval Philosophy; Thomas Gilby, Poetic Experience: An Introduction to Thomist Aesthetic; and Joseph Pohle, Grace, Actual and Habitual: A Dogmatic Treatise.
 Summa Theologica, 1a 2ae, q.109, a.4, r.1.
 Summa Theologica, 1a, q.1, a.1, r.1.
 Summa Theologica, 1a, q.1, a.1, q.1, a.5, 1a 2ae, q.109, a.4, r.1.
 Summa Theologica, 1a, q.1, a.1, q.1, a.5; Summa Contra Gentiles, I, iv, 6.
 Summa Contra Gentiles, I, vii, 7.
 Summa Theologica, 1a, q.1, a.6, r.2.
 Summa Theologica, 1a 2ae, q.113, a.4.
 Summa Theologica, 1a 2ae, q.28, a.1-2; 2a 2ae, q.27, a.4.
 Summa Theologica, 1a 2ae, q.109, a.4c.
 Summa Contra Gentiles, V, liv, 9.
 Summa Theologica, 3a, q.49, a.1c.
 Summa Theologica, 3a, q.49, a.2.
 Summa Theologica, 3a, q.62, a.5.
 Summa Theologica, 1a 2ae, q.109, a9c, q.114, a.3c.
 Summa Theologica, 1a 2ae, q.3, a.8; q.5, a.5; q.114, a.4.