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Thomas Aquinas

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Thomas Aquinas
Era Medieval Philosophy
Region Western Philosophers
School Scholasticism, Founder of Thomism
Main interests Metaphysics (incl. Theology), Logic, Mind, Epistemology, Ethics, Politics
Notable ideas Five Proofs for God's Existence, Principle of double effect

Saint Thomas Aquinas, O.P. (also Thomas of Aquin or Aquino; c. 1225 – 7 March 1274) was an Italian Catholic priest in the Dominican Order, a philosopher and theologian in the scholastic tradition, known as Doctor Angelicus, Doctor Universalis and Doctor Communis. He was the foremost classical proponent of natural theology, and the father of the Thomistic school of philosophy and theology.

Aquinas is held in the Catholic Church to be the model teacher for those studying for the priesthood (Code of Canon Law, Can. 252, §3). The works for which he is best-known are the Summa Theologica and the Summa Contra Gentiles. One of the 33 Doctors of the Church, he is considered by many Catholics to be the Catholic Church's greatest theologian and philosopher. Consequently, many institutions of learning have been named after him.


Early life

Aquinas was born c. 1225 at his father Count Landulph's castle of Roccasecca in the Kingdom of Sicily, in the present-day Regione Lazio. Through his mother, Theodora Countess of Theate, Aquinas was related to the Hohenstaufen dynasty of Holy Roman emperors. Landulf's brother Sinibald was abbot of the original Benedictine monastery at Monte Cassino. The family intended for Aquinas to follow his uncle into that position. This would have been a normal career path for a younger son of southern Italian nobility.

At the age of five, Aquinas began his early education at a monastery. When he was 16, he went to the University of Naples, where he studied for six years. Aquinas had come under the influence of the Dominicans, who wished to enlist the ablest young scholars of the age. The Dominicans and the Franciscans represented a revolutionary challenge to the well-established clerical systems of Medieval Europe.

Aquinas's change of heart did not please his family. On the way to Rome, his brothers seized him and took him back to his parents at the castle of San Giovanni. He was held captive for a year so he would renounce his new aspiration. According to Aquinas's earliest biographers, two of his brothers even brought a prostitute to tempt him, but he drove her away. After this, it is said that two angels came down from the heavens and girded his loins, providing Aquinas with a life of chastity. Finally, Pope Innocent IV intervened and Aquinas assumed the habit of St. Dominic in his 17th year.

His superiors saw his great aptitude for theological study. In late 1244, they sent him to the Dominican school in Cologne, where Albertus Magnus was lecturing on philosophy and theology. In 1245, Aquinas accompanied Albertus to the University of Paris, where they remained for three years. During this time, Aquinas threw himself into the controversy between the university and the Friar-Preachers about the liberty of teaching. Aquinas actively resisted the university's speeches and pamphlets. When the Pope was alerted of this dispute, the Dominicans selected Aquinas to defend his order. He did so with great success. He even overcame the arguments of Guillaume de St Amour, the champion of the university, and one of the most celebrated men of the day.

Aquinas then graduated as a bachelor of theology. In 1248, he returned to Cologne, where he was appointed second lecturer and magister studentium. This year marks the beginning of his literary activity and public life.

For several years, Aquinas remained with Albertus Magnus. Aquinas's long association with this great philosopher-theologian was the most important influence in his development. In the end, he became a comprehensive scholar who permanently utilized Aristotle's method.

Saint Thomas Aquinas

St. Thomas Aquinas, by Fra Angelico
Doctor of the Church
Born c. 1225
Roccasecca, near Naples, Italy
Died March 7, 1274(1274-03-07) (aged 49)
Fossanuova Abbey, Italy
Honored in Roman Catholic Church
Canonized July 18, 1323, Avignon, France
Major shrine Church of the Jacobins, Toulouse, France
Feast January 28 (new), March 7 (old)
Attributes The Summa Theologica, a model church, the Sun
Patronage All Catholic educational institutions


In 1252, Aquinas went to Paris for his master's degree.

In 1256, Aquinas, along with his friend Bonaventura, began to lecture on theology in Paris and Rome and other Italian towns. From this time on, his life was one of incessant toil. Aquinas continually served in his order, frequently made long and tedious journeys, and constantly advised the reigning pontiff on affairs of state.

In 1259, Aquinas was present at an important meeting of his order at Valenciennes. At the solicitation of Pope Urban IV, he moved to Rome no earlier than late 1261. In 1263, he attended the London meeting of the Dominican order. In 1268, he lectured in Rome and Bologna. Throughout these years, he remained engaged in the public business of the Catholic Church.

From 1269 to 1271, Aquinas was again active in Paris. He lectured to the students, managed the affairs of the Catholic Church, and advised the king, Louis VIII, his kinsman, on affairs of state. In 1272, the provincial chapter at Florence empowered him to begin a new stadium generale at a location of his choice. Later, the chief of his order and King Charles II brought him back to the professor's chair at Naples.

All this time, Aquinas preached every day, and he wrote homilies, disputations, and lectures. He also worked diligently on his great literary work, the Summa Theologica. The Catholic Church offered to make him archbishop of Naples and abbot of Monte Cassino, but he refused both.

It should be noted that, as a Dominican Friar, Aquinas was supposed to participate in the mortification process. He did not; a remarkable thing considering how devoted to his faith he was known to be. At his canonization trial, it became evident he did not practice such rites. "The forty-two witnesses at the canonization trial had little to report concerning extraordinary acts of penance, sensational deeds, and mortifications...they could only repeat unanimously, again and again: Thomas had been a pure person, humble, simple, peace-loving, given to contemplation, moderate, a lover of poetry". These endearing qualities helped him in his beatification. The witnesses praised Thomas for his rational thought.

It is reported in Chesterton's book that Aquinas placed his essay concerning the Eucharist at the bottom of the cross. The friars there claimed to see the image of Jesus descending upon it, and a voice was heard to say, "Thomas, thou hast written well concerning the sacrament of My Body.”On one occasion, monks claimed to have found him levitating. The twentieth century Catholic writer/convert G.K. Chesterton describes these and other stories in his work on Aquinas, The Dumb Ox, a title based on early impressions that Aquinas was not proficient in speech. Chesterton quotes Albertus Magnus' refutation of these impressions: "You call him 'a dumb ox,' but I declare before you that he will yet bellow so loud in doctrine that his voice will resound through the whole world."

Aquinas had a dark complexion, large head and receding hairline, and he was of large stature. His manners showed his breeding, for people described him as refined, affable and lovable. In arguments, he maintained self-control and won over his opponents by his personality and great learning. His tastes were simple. He impressed his associates with his power of memory. When absorbed in thought, he often forgot his surroundings, but he was able to express his thoughts systematically, clearly and simply. Because of his keen grasp of his materials, Aquinas does not make the reader his companion in the search for truth; rather, he teaches authoritatively. On the other hand, he felt dissatisfied by the insufficiency of his works as compared to the divine revelations he had received.

He is said to have spoken on the morning of December 6, 1273, his last words: "Such secrets have been revealed to me that all I have written now appears of little value."

Condemnation, death, and canonization

In 1270, the bishop of Paris issued an edict condemning a number of teachings then current at the university, which derived from Aristotle or from Arabic philosophers such as Averroes. The teachings of Thomas were among those targeted. This condemnation gave rise to an investigation in Paris, in response to which the Dominican order prudently moved Thomas to Italy. Eventually, in 1277 (three years after Thomas's death), the bishop of Paris issued another, more detailed edict in which he condemned a series of Thomas's theses as heretical, and excommunicated Thomas posthumously. The bishop of Oxford issued a similar condemnation a few months later. These condemnations echoed the orthodox Augustinian theology of the day, which considered human reason inadequate to understand the will of God.

The 1277 condemnation "has often been depicted as the most dramatic and significant doctrinal censure in the history of the University of Paris, and a landmark in the history of medieval philosophy and theology." In fact, it took many years for Thomas's reputation to recover from this censure.

In January 1274, Pope Gregory X directed Thomas to attend the Second Council of Lyons. Aquinas's task was to investigate and, if possible, settle the differences between the Greek and Latin churches. Far from healthy, he undertook the journey. On the way, he stopped at the castle of a niece and there became seriously ill. Aquinas desired to end his days in a monastery. However, he was unable to reach a house of the Dominicans, so he was taken to the Cistercian monastery of Fossa Nuova. After a lingering illness of seven weeks, Aquinas died on March 7, 1274.

In The Divine Comedy, Dante sees the glorified spirit of Aquinas in the Heaven of the Sun with the other great exemplars of religious wisdom. Dante also asserts that Aquinas died by poisoning, on the order of Charles of Anjou (Purg. xx. 69). Villani (ix. 218) cites this belief, and the Anonimo Fiorentino describes the crime and its motive. But the historian Muratori reproduces the account made by one of Aquinas's friends, and this version of the story gives no hint of foul play.

Fifty years after Thomas's death, Pope John XXII, seated in Avignon, pronounced Thomas a saint of the Catholic church. Thomas's theology had begun its rise to prestige. Two centuries later, in 1567, Pope Pius V ranked the festival of St. Thomas Aquinas with those of the four great Latin fathers: Ambrose, Augustine, Jerome, and Gregory. However, in the same period the Council of Trent would still turn to Duns Scotus before Thomas, as a source of arguments in defence of the Catholic Church. It was not until the First Vatican Council that Thomas was elevated to the preeminent status of "teacher of the church" which he enjoys today.

In his Encyclical of August 4, 1879, Pope Leo XIII stated that Aquinas's theology was a definitive exposition of Catholic doctrine. Thus, he directed the clergy to take the teachings of Aquinas as the basis of their theological positions. Leo XIII also decreed that all Catholic seminaries and universities must teach Aquinas's doctrines, and where Aquinas did not speak on a topic, the teachers were "urged to teach conclusions that were reconcilable with his thinking." In 1880, Aquinas was declared patron of all Catholic educational establishments.

In a monastery at Naples, near the cathedral of St. Januarius, a cell in which he supposedly lived is still shown to visitors. His remains were placed in the Church of the Jacobins in Toulouse in 1369. Between 1789 and 1974, they were held in Saint Sernin basilica of Toulouse. In 1974, they were returned to the Church of the Jacobins, where they have remained ever since.

The Roman Catholic Church today celebrates his feast on January 28, the date of publication of the Summa. Before the revision of the Roman calendar in 1969 the feast was observed on March 7, the day of his death. The March 7 date is still used today for the traditional Latin Mass, a first class feast day in schools.


"Nihil est in intellectu quod non sit prius in sensu." (Nothing is in the intellect that was not first in the senses) – Aquinas's peripatetic axiom

The philosophy of Aquinas has exerted enormous influence on subsequent Christian theology, especially that of the Roman Catholic Church, extending to Western philosophy in general, where he stands as a vehicle and modifier of Aristotelianism. Philosophically, his most important and enduring work is the Summa Theologica, in which he expounds his systematic theology of the quinquae viae.


Aquinas believed "that for the knowledge of any truth whatsoever man needs Divine help, that the intellect may be moved by God to its act." However, he believed that human beings have the natural capacity to know many things without special divine revelation, even though such revelation occurs from time to time, "especially in regard to [topics of] faith." Aquinas was also an Aristotelian and an empiricist. He substantially influenced these two streams of Western thought.


Aquinas believed that truth is known through reason (natural revelation) and faith (supernatural revelation). Supernatural revelation is revealed through the prophets, Holy Scripture, and the Magisterium, the sum of which is called "Tradition". Natural revelation is the truth available to all people through their human nature; certain truths all men can attain from correct human reasoning. For example, he felt this applied to rational proofs for the existence of God.

Though one may deduce the existence of God and His Attributes (One, Truth, Good, Power, Knowledge) through reason, certain specifics may be known only through special revelation (Like the Trinity). In Aquinas's view, special revelation is equivalent to the revelation of God in Jesus Christ. The major theological components of Christianity, such as the Trinity and the Incarnation, are revealed in the teachings of the Catholic Church and the Scriptures and may not otherwise be deduced.

Supernatural revelation (faith) and natural revelation (reason) are complementary rather than contradictory in nature, for they pertain to the same unity: truth.


An important element in Aquinas's philosophy is his theory of analogy. Aquinas noted three forms of descriptive language: univocal, analogical, and equivocal.

  • Univocality is the use of a descriptor in the same sense when applied to two objects or groups of objects. For instance, when the word "milk" is applied both to milk produced by cows and by any other female mammal.
  • Analogy, Aquinas maintained, occurs when a descriptor changes some but not all of its meaning. For example, the word "healthy" is analogical in that it applies both to a healthy person or animal (those that enjoy of good health) and to some food or drink (if it is good for the health). Analogy is necessary when talking about God, for some of the aspects of the divine nature are hidden (Deus absconditus) and others revealed (Deus revelatus) to finite human minds. In Aquinas's mind, we can know about God through his creation (general revelation), but only in an analogous manner. We can speak of God's goodness only by understanding that goodness as applied to humans is similar to, but not identical with, the goodness of God.
  • Equivocation is the complete change in meaning of the descriptor and is an informal fallacy. For example, when the word "bank" is applied to river banks and financial banks. Modern philosophers talk of ambiguity.


Aquinas's ethics are based on the concept of "first principles of action." In his Summa Theologica, he wrote:

Virtue denotes a certain perfection of a power. Now a thing's perfection is considered chiefly in regard to its end. But the end of power is act. Wherefore power is said to be perfect, according as it is determinate to its act.

Aquinas defined the four cardinal virtues as prudence, temperance, justice, and fortitude. The cardinal virtues are natural and revealed in nature, and they are binding on everyone. There are, however, three theological virtues: faith, hope, and charity. These are supernatural and are distinct from other virtues in their object, namely, God:

Now the object of the theological virtues is God Himself, Who is the last end of all, as surpassing the knowledge of our reason. On the other hand, the object of the intellectual and moral virtues is something comprehensible to human reason. Wherefore the theological virtues are specifically distinct from the moral and intellectual virtues.

Furthermore, Aquinas distinguished four kinds of law: eternal, natural, human, and divine. Eternal law is the decree of God that governs all creation. Natural law is the human "participation" in the eternal law and is discovered by reason. Natural law, of course, is based on "first principles":

. . . this is the first precept of the law, that good is to be done and promoted, and evil is to be avoided. All other precepts of the natural law are based on this . . .

The desire to live and to procreate are counted by Aquinas among those basic (natural) human values on which all human values are based.

Human law is positive law: the natural law applied by governments to societies. Divine law is the specially revealed law in the scriptures.

Aquinas also greatly influenced Catholic understandings of mortal and venial sins.

Aquinas denied that human beings have any duty of charity to animals because they are not persons. Otherwise, it would be unlawful to use them for food. But this does not give us license to be cruel to them, for "cruel habits might carry over into our treatment of human beings."

17th century sculpture of Thomas Aquinas.


Aquinas viewed theology, or the sacred doctrine, as a science, the raw material data of which consists of written scripture and the tradition of the Catholic church. These sources of data were produced by the self-revelation of God to individuals and groups of people throughout history. Faith and reason, while distinct but related, are the two primary tools for processing the data of theology. Aquinas believed both were necessary - or, rather, that the confluence of both was necessary - for one to obtain true knowledge of God. Aquinas blended Greek philosophy and Christian doctrine by suggesting that rational thinking and the study of nature, like revelation, were valid ways to understand God. According to Aquinas, God reveals himself through nature, so to study nature is to study God. The ultimate goals of theology, in Aquinas’ mind, are to use reason to grasp the truth about God and to experience salvation through that truth.

Nature of God

Aquinas believed that the existence of God is neither self-evident nor beyond proof. In the Summa Theologica, he considered in great detail five rational proofs for the existence of God. These are widely known as the quinquae viae, or the "Five Ways."

Concerning the nature of God, Aquinas felt the best approach, commonly called the via negativa, is to consider what God is not. This led him to propose five positive statements about the divine qualities:

  1. God is simple, without composition of parts, such as body and soul, or matter and form.
  2. God is perfect, lacking nothing. That is, God is distinguished from other beings on account of God's complete actuality.
  3. God is infinite. That is, God is not finite in the ways that created beings are physically, intellectually, and emotionally limited. This infinity is to be distinguished from infinity of size and infinity of number.
  4. God is immutable, incapable of change on the levels of God's essence and character.
  5. God is one, without diversification within God's self. The unity of God is such that God's essence is the same as God's existence. In Aquinas's words, "in itself the proposition 'God exists' is necessarily true, for in it subject and predicate are the same."

In this approach, he is following, among others, the Jewish philosopher Maimonides.

Nature of the Trinity

Aquinas argued that God, while perfectly united, also is perfectly described by Three Interrelated Persons. These three persons (Father, Son, and Holy Spirit) are constituted by their relations within the essence of God. The Father generates the Son (or the Word) by the relation of self-awareness. This eternal generation then produces an eternal Spirit "who enjoys the divine nature as the Love of God, the Love of the Father for the Word."

This Trinity exists independently from the world. It transcends the created world, but the Trinity also decided to communicate God's self and God's goodness to human beings. This takes place through the Incarnation of the Word in the person of Jesus Christ and through the indwelling of the Holy Spirit (indeed, the very essence of the Trinity itself) within those who have experienced salvation by God.

Nature of Jesus Christ

In the Summa Theologica, Aquinas begins his discussion of Jesus Christ by recounting the biblical story of Adam and Eve and by describing the negative effects of original sin. The purpose of Christ's Incarnation was to restore human nature by removing "the contamination of sin", which humans cannot do by themselves. "Divine Wisdom judged it fitting that God should become man, so that thus one and the same person would be able both to restore man and to offer satisfaction."

Aquinas argued against several specific contemporary and historical theologians who held differing views about Christ. In response to Photinus, Aquinas stated that Jesus was truly divine and not simply a human being. Against Nestorius, who suggested that God merely inhabited the body of Christ, Aquinas argued that the fullness of God was an integral part of Christ's existence. However, countering Apollinaris' views, Aquinas held that Christ had a truly human (rational) soul, as well. This produced a duality of natures in Christ, contrary to the teachings of Arius. Aquinas argued against Eutyches that this duality persisted after the Incarnation. Aquinas stated that these two natures existed simultaneously yet distinguishably in one real human body, unlike the teachings of Manichaeus and Valentinus.

In short, "Christ had a real body of the same nature of ours, a true rational soul, and, together with these, perfect Deity." Thus, there is both unity (in his one hypostasis) and diversity (in his two natures, human and Divine) in Christ.

Goal of human life

In Aquinas's thought, the goal of human existence is union and eternal fellowship with God. Specifically, this goal is achieved through the beatific vision, an event in which a person experiences perfect, unending happiness by comprehending the very essence of God. This vision, which occurs after death, is a gift from God given to those who have experienced salvation and redemption through Christ while living on earth.

This ultimate goal carries implications for one's present life on earth. Aquinas stated that an individual's will must be ordered toward right things, such as charity, peace, and holiness. He sees this as the way to happiness. Aquinas orders his treatment of the moral life around the idea of happiness. The relationship between will and goal is antecedent in nature "because rectitude of the will consists in being duly ordered to the last end [that is, the beatific vision]." Those who truly seek to understand and see God will necessarily love what God loves. Such love requires morality and bears fruit in everyday human choices.

Modern influence

Many modern ethicists both within and outside the Catholic Church (notably Philippa Foot and Alasdair MacIntyre) have recently commented on the possible use of Aquinas's virtue ethics as a way of avoiding utilitarianism or Kantian deontology. Through the work of twentieth century philosophers such as Elizabeth Anscombe (especially in her book Intention), Aquinas's principle of double effect specifically and his theory of intentional activity generally have been influential.

It is remarkable that Aquinas's aesthetic theories, especially the concept of claritas, deeply influenced the literary practice of modernist writer James Joyce, who used to extol Aquinas as being second only to Aristotle among Western philosophers. The influence of Aquinas's aesthetics also can be found in the works of the Italian semiotician Umberto Eco, who wrote an essay on aesthetic ideas in Aquinas (published in 1956 and republished in 1988 in a revised edition).

Other views


For Aquinas' writing justifying the sacraments, see Aquinas and the Sacraments.

Various topics

For Aquinas' discussion of the death penalty, usury, existentialism, and forced baptism of the children of Jews and other heretics, see Thought of Thomas Aquinas.


Many biographies of Aquinas have been written over the centuries, one of the most notable by G. K. Chesterton.

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