Thomas Aquinas, sometimes called the Angelic Doctor and the Prince of Scholastics, was born at Roccasecca in the ancient Kingdom of Sicily. At about the age of 5 he was placed by his parents in the Benedictine monastery at Monte Cassino, and years later proceeded to the University of Naples where he came into contact with members of the Dominican order. Against the violent opposition of his family, he became a Dominican friar in 1244.

From 1245-1252 he studied under the German Scholastic philosopher Albertus Magnus, then went to Paris to teach at the Dominican studium generale. Because Aquinas was heavyset and taciturn, his fellow novices called him Dumb Ox, but Albertus Magnus is said to have predicted that "this ox will one day fill the world with his bellowing."

Aquinas was ordained a priest about 1250, and he began to teach at the University of Paris in 1252. His first writings, primarily summaries and amplifications of his lectures, appeared two years later. His first major work was Scripta Super Libros Sententiarum (Writings on the Books of the Sentences, 1256?), which consisted of commentaries on an influential work concerning the sacraments of the church, known as the Sententiarum Libri Quatuor (Four Books of Sentences), by the Italian theologian Peter Lombard. In 1256 Aquinas was awarded a doctorate in theology and appointed professor of philosophy at the University of Paris. Pope Alexander IV (reigned 1254-61) summoned him to Rome in 1259, where he acted as adviser and lecturer to the papal court. Returning to Paris in 1268, Aquinas immediately became involved in a controversy with the French philosopher Siger de Brabant and other followers of the Islamic philosopher Averro?s. In 1274 Thomas fell ill and died in the Cistercian abbey of Fossanova on March 7.

Aquinas was influenced by the writings of Aristotle, the Muslim Aristotelians Averro?s and Avicenna, and the Jewish philosopher Maimonides. Unlike many theologians, he welcomed the Latin translation of Aristotle’s complete writings. Aquinas meant to take Aristotle’s philosophical arguments to their deepest level, not just to fit them into the existing theological framework. He pressed the distinction between potentiality and actuality and defended immortality without diminishing the doctrine that the soul is embodied.

His definition of philosophical disciplines starts with logic, which are the mental constructions we place on our experience. Theoretical philosophy isolates what is constant in changing facts, and is divided into 1) natural philosophy, the study of objects of material processes, 2) mathematical philosophy, the study of quantity without need to appeal to the sensible world, and 3) metaphysical philosophy, the study of the non-material. Moral philosophy studies personal ethics, economics, and politics.

Aquinas insisted that the truths of faith and those of sense experience, as presented by Aristotle, are fully compatible and complementary. Some truths, such as that of the mystery of the incarnation, can be known only through revelation, and others, such as that of the composition of material things, only through experience; still others, such as that of the existence of God, are known through both equally. All knowledge, Aquinas held, originates in sensation, but sense data can be made intelligible only by the action of the intellect, which elevates thought toward the apprehension of such immaterial realities as the human soul, the angels, and God. To reach understanding of the highest truths, those with which religion is concerned, the aid of revelation is needed. Aquinas’s moderate realism placed the universals firmly in the mind, in opposition to extreme realism, which posited their independence of human thought. He admitted a foundation for universals in existing things, however, in opposition to nominalism and conceptualism.

Aquinas saw ideas as embodied here and now about us. Substance and accidents are the first categories of the material world, and material processes are shaped by the four causes - material, formal, efficient, and final. All material substances are composed of matter and form. His rejection of Neoplatonism scandalized some of his contemporaries; he was critical of the conception of humans as rational souls inhabiting powerless, material bodies. Like Aristotle, he saw the human being as a complete union of soul and body, of matter and form. Thus, in addition to the survival of the soul after death, the resurrection of the body seemed philosophically appropriate as well as religiously true.

Aquinas’ synthesis of the divisions of Law dominates his political philosophy. Law is rational, it is for the common good of a communion of people. The Eternal Law in the mind of God is the exemplar of all law and is impressed on human minds as Natural Law. In contrast stands Positive Law which may sometimes reinforce Natural Law as pragmatic supplements to make the good life easier or to safeguard public order. He departed from the traditional Augustinian view that civil power was a remedy against our antisocial appetites, and revived Aristotle’s idea of the State meeting the essential demands of human nature. Human legislation should know its limits, and not seek to cover the whole field of morality.

Aquinas’s accomplishment was immense; his work marks one of the few great culminations in the history of philosophy. After Aquinas, Western philosophers could choose only between humbly following him and striking off in some altogether different direction. In the centuries immediately following his death, the dominant tendency, even among Roman Catholic thinkers, was to adopt the second alternative. Interest in Thomist philosophy began to revive, however, toward the end of the 19th century. In the encyclical Aeterni Patris (Of the Eternal Father, 1879), Pope Leo XIII recommended that St. Thomas’s philosophy be made the basis of instruction in all Roman Catholic schools. Pope Pius XII, in the encyclical Humani Generis (Of the Human Race, 1950), affirmed that the Thomist philosophy is the surest guide to Roman Catholic doctrine and discouraged all departures from it. Thomism remains a leading school of contemporary thought. 

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