St Thomas Aquinas
Thomas Aquinas depicted in stained glass
Born	Thomas Aquinas 1225 Roccasecca, Kingdom of Sicily
Died	7 March 1274 Fossanova, Kingdom of Sicily
Occupation	Priest, Philosopher, Theologian
Nationality	Italian
Genres	Scholasticism, Thomism
Subjects	Metaphysics, Logic, Theology, Mind, Epistemology, Ethics, Politics
Notable work(s)	Summa Theologica, Summa Contra Gentiles
Influences Aristotle, Averroes, Avicenna, Albertus Magnus, Paul the Apostle, Boethius, Eriugena, Anselm, Maimonides, Augustine of Hippo, John of Damascus
Influenced Giles of Rome, Godfrey of Fontaines, Hooker, Locke, Dante, Leibniz, Martain, Gilson, Anscombe, Donoso Cortés, Eckhart, Chesterton, Joyce, Kenny, Pope Pius XII, Carvalho, Walker Percy; See also Thomism, Roman Catholic theology, Mortimer J. Adler, Cornelio Fabro, Fulton J. Sheen, Reginald Garrigou-Lagrange

Thomas Aquinas, O.P. ( /əˈkwaɪnəs/ ə-KWY-nəs; 1225 – 7 March 1274), also Thomas of Aquin or Aquino, was an Italian Dominican priest of the Roman Catholic Church, and an immensely influential philosopher and theologian in the tradition of scholasticism, known as Doctor Angelicus ([the] Angelic Doctor), Doctor Communis, or Doctor Universalis.^[1] "Aquinas" is not a surname, but is a Latin demonym for a resident of Aquino, his place of birth. He was the foremost classical proponent of natural theology, and the father of Thomism. His influence on Western thought is considerable, and much of modern philosophy was conceived as a reaction against, or as an agreement with, his ideas, particularly in the areas of ethics, natural law, metaphysics, and political theory.

Thomas is held in the Catholic Church to be the model teacher for those studying for the priesthood.^[2] The works for which he is best-known are the Summa Theologica and the Summa Contra Gentiles. As one of the 33 Doctors of the Church, he is considered the Church's greatest theologian and philosopher. Pope Benedict XV declared: "This (Dominican) Order ... acquired new luster when the Church declared the teaching of Thomas to be her own and that Doctor, honored with the special praises of the Pontiffs, the master and patron of Catholic schools."^[3]

Biography[link]

Dominican (1225–1244)[link]

Thomas was born in Roccasecca c. January 28, 1225, according to some authors in the castle of his father, the Count Landulf of Aquino, placed in Roccasecca, in the same Contea di Aquino (Kingdom of Sicily, in the present-day: Italy, in the Lazio, province). Thomas was of Langobardic origin by his father and through his mother, Theodora Countess of Theate, he was related to the Hohenstaufen dynasty of Holy Roman emperors.^{[4][not in citation given]} Landulf's brother Sinibald was abbot of the original Benedictine abbey at Monte Cassino. While the rest of the family's sons pursued military careers,^[5] the family intended for Thomas to follow his uncle into the abbacy;^[6] this would have been a normal career path for a younger son of southern Italian nobility.^[4]

At the age of five, Thomas began his early education at Monte Cassino but after the military conflict that broke out between the Emperor Frederick II and Pope Gregory IX spilled into the abbey in early 1239, Landulf and Theodora had Thomas enrolled at the studium generale (university) recently established by Frederick in Naples.^[7] It was here that Thomas was probably introduced to Aristotle, Averroes and Maimonides, all of whom would influence his theological philosophy.^[8] It was also during his study at Naples that Thomas came under the influence of John of St. Julian, a Dominican preacher in Naples, who was part of the active effort by the Dominican order to recruit devout followers.^[9] Here his teacher in arithmetic, geometry, astronomy, and music was Petrus de Ibernia.^[10]

The Castle of Monte San Giovanni Campano

At age nineteen, Thomas resolved to join the Dominican Order. Thomas's change of heart did not please his family, who had expected him to become a Benedictine monk.^[11] In an attempt to prevent Theodora's interference in Thomas's choice, the Dominicans arranged for Thomas to be removed to Rome, and from Rome, sent to Paris.^[12] On his way to Rome, his brothers, per Theodora's instructions, seized him as he was drinking from a spring and took him back to his parents at the castle of Monte San Giovanni Campano.^[12] He was held for two years in the family homes at Monte San Giovanni and Roccasecca in an attempt to prevent him from assuming the Dominican habit and to push him into renouncing his new aspiration.^[8] Political concerns prevented the Pope from ordering Thomas's release, extending the detention,^[13] a detention which Thomas spent tutoring his sisters and communicating with members of the Dominican Order.^[8] Family members became desperate to dissuade Thomas, who remained determined to join the Dominicans. At one point, two of his brothers hired a prostitute to seduce him, but he drove her away, wielding a burning stick. According to legend, that night two angels appeared to him as he slept and strengthened his determination to remain celibate.^[14] By 1244, seeing that all of her attempts to dissuade Thomas had failed, Theodora sought to save the family's dignity, arranging for Thomas to escape at night through his window. In her mind, a secret escape from detention was less damaging than an open surrender to the Dominicans. Thomas was sent first to Naples and then to Rome to meet Johannes von Wildeshausen, the Master General of the Dominican Order.^[15]

Paris, Cologne, Albert Magnus, and first Paris regency (1245–1259)[link]

In 1245, Thomas was sent to study at the University of Paris' Faculty of Arts where he most likely met Dominican scholar Albertus Magnus,^[16] then the Chair of Theology at the College of St. James in Paris.^[17] When Albertus was sent by his superiors to teach at the new studium generale at Cologne in 1248,^[16] Thomas followed him, declining Pope Innocent IV's offer to appoint him abbot of Monte Cassino as a Dominican.^[6] Albertus then appointed the reluctant Thomas magister studentium.^[4] When Thomas failed his first theological disputation, Albertus prophetically exclaimed: "We call him the dumb ox, but in his teaching he will one day produce such a bellowing that it will be heard throughout the world."^[6]

Thomas taught in Cologne as an apprentice professor (baccalaureus biblicus), instructing students on the books of the Old Testament and writing Expositio super Isaiam ad litteram (Literal Commentary on Isaiah), Postilla super Ieremiam (Commentary on Jeremiah) and Postilla super Threnos (Commentary on Lamentations).^[18] Then in 1252 he returned to Paris to study for the master's degree in theology. He lectured on the Bible as an apprentice professor, and upon becoming a baccalaureus Sententiarum (bachelor of the Sentences)^[19] devoted his final three years of study to commenting on Peter Lombard's Sentences. In the first of his four theological syntheses, Thomas composed a massive commentary on the Sentences entitled Scriptum super libros Sententiarium (Commentary on the Sentences). Aside from his masters writings, he wrote De ente et essentia (On Being and Essence) for his fellow Dominicans in Paris.^[6]

In the spring of 1256, Thomas was appointed regent master in theology at Paris and one of his first works upon assuming this office was Contra impugnantes Dei cultum et religionem (Against Those Who Assail the Worship of God and Religion), defending the mendicant orders which had come under attack by William of Saint-Amour.^[20] During his tenure from 1256 to 1259, Thomas wrote numerous works, including: Questiones disputatae de veritate (Disputed Questions on Truth), a collection of twenty-nine disputed questions on aspects of faith and the human condition^[21] prepared for the public university debates he presided over on Lent and Advent;^[22] Quaestiones quodlibetales (Quodlibetal Questions), a collection of his responses to questions posed to him by the academic audience;^[21] and both Expositio super librum Boethii De trinitate (Commentary on Boethius's De trinitate) and Expositio super librum Boethii De hebdomadibus (Commentary on Boethius's De hebdomadibus), commentaries on the works of 6th century philosopher Anicius Manlius Severinus Boethius.^[23] By the end of his regency, Thomas was working on one of his most famous works, Summa contra Gentiles.^[24]

Saint Thomas Aquinas
St. Thomas Aquinas by Fra Bartolomeo
Doctor of the Church
Born	c. 1225 Aquino, Kingdom of Sicily
Died	7 March 1274 Fossanova Abbey, Kingdom of Sicily
Honored in	Roman Catholic Church Anglican Communion Lutheranism
Canonized	July 18,1323, Avignon, France by Pope John XXII
Major shrine	Church of the Jacobins, Toulouse, France
Feast	28 January (new), 7 March (old)
Attributes	The Summa Theologica, a model church, the Sun
Patronage	Academics; against storms; against lightning; apologists; Aquino, Italy; Belcastro, Italy; book sellers; Catholic academies, schools, and universities; chastity; Falerna, Italy; learning; pencil makers; philosophers; publishers; scholars; students; theologians.[25]

Naples, Orvieto, Rome, and Santa Sabina (1259–1269)[link]

Around 1259, Thomas returned to Naples where he lived until he arrived in Orvieto around September 1261. In Orvieto, he was appointed conventual lector, in charge of the education of friars unable to attend a studium generale. During his stay in Orvieto, Thomas completed his Summa contra Gentiles, and wrote the Catena Aurea (The Golden Chain).^[26] He also wrote the liturgy for the newly created feast of Corpus Christi and produced works for Pope Urban IV concerning Greek Orthodox theology, e.g. Contra errores graecorum (Against the Errors of the Greeks).^[24] In 1265 he was ordered by the Dominican Chapter of Agnani to establish a studium for the Order in Rome at the priory of Santa Sabina.^[27][28] He remained there from 1265 until he was called back to Paris in 1268.^[29] It was in Rome that Thomas began his most famous work, Summa Theologica,^[26] and wrote a variety of other works like his unfinished Compendium Theologiae and Responsio ad fr. Ioannem Vercellensem de articulis 108 sumptis ex opere Petri de Tarentasia (Reply to Brother John of Vercelli Regarding 108 Articles Drawn from the Work of Peter of Tarentaise).^[23] In his position as head of the studium, conducted a series of important disputations on the power of God, which he compiled into his De potentia.^[29]

The quarrelsome second Paris regency (1269–1272)[link]

In 1268 the Dominican Order assigned Thomas to be regent master at the University of Paris for a second time, a position he held until the spring of 1272. Part of the reason for this sudden reassignment appears to have arisen from the rise of "Averroism" or "radical Aristotelianism" in the universities. In response to these perceived evils, Thomas wrote two works, one of them being De unitate intellectus, contra Averroistas (On the Unity of Intellect, against the Averroists) in which he blasts Averroism as incompatible with Christian doctrine.^[30] During his second regency, he finished the second part of the Summa and wrote De virtutibus and De aeternitate mundi,^[29] the latter of which dealt with controversial Averroist and Aristotelian beginninglessness of the world.^[31] Disputes with some important Franciscans such as Bonaventure and John Peckham conspired to make his second regency much more difficult and troubled than the first. A year before Thomas re-assumed the regency at the 1266–67 Paris disputations, Franciscan master William of Baglione accused Thomas of encouraging Averroists, calling him the "blind leader of the blind". Thomas called these individuals the murmurantes (Grumblers).^[31] In reality, Thomas was deeply disturbed by the spread of Averroism and was angered when he discovered Siger of Brabant teaching Averroistic interpretations of Aristotle to Parisian students.^[32] On 10 December 1270, the bishop of Paris, Etienne Tempier, issued an edict condemning thirteen Aristotlelian and Averroistic propositions as heretical and excommunicating anyone who continued to support them.^[33] Many in the ecclesiastical community, the so-called Augustinians, were fearful that this introduction of Aristotelianism and the more extreme Averroism might somehow contaminate the purity of the Christian faith. In what appears to be an attempt to counteract the growing fear of Aristotelian thought, Thomas conducted a series of disputations between 1270 and 1272: De virtutibus in communi (On Virtues in General), De virtutibus cardinalibus (On Cardinal Virtues), De spe (On Hope).^[34]

Final days and "Straw" (1272–1274)[link]

In 1272 Thomas took leave from the University of Paris when the Dominicans from his home province called upon him to establish a studium generale wherever he liked and staff it as he pleased. He chose to establish the institution in Naples, and moved there to take his post as regent master.^[29] He took his time at Naples to work on the third part of the Summa while giving lectures on various religious topics. On 6 December 1273 Thomas was celebrating the Mass of St. Nicholas when, according to some, he heard Christ speak to him. Christ asked him what he desired, being pleased with his meritorious life. Thomas replied "Only you Lord. Only you."^[35] After this exchange something happened, but Thomas never spoke of it or wrote it down. Because of what he saw, he abandoned his routine and refused to dictate to his socius Reginald of Piperno. When Reginald begged him to get back to work, Thomas replied: "Reginald, I cannot, because all that I have written seems like straw to me."^[36] (mihi videtur ut palea).^[37] What exactly triggered Thomas's change in behavior is believed by Catholics to have been some kind of supernatural experience of God.^[38] After taking to his bed, he did recover some strength.^[39]

Looking to find a way to reunite the Eastern Orthodox churches with the Catholic Church (the Eastern Orthodox were excommunicated by the Roman Catholic Church, and vice versa, in A.D. 1054 over doctrinal disputes) Pope Gregory X convened the Second Council of Lyon to be held on 1 May 1274 and summoned Thomas to attend.^[40] At the meeting, Thomas's work for Pope Urban IV concerning the Greeks, Contra errores graecorum, was to be presented.^[41] On his way to the Council, riding on a donkey along the Appian Way,^[40] he struck his head on the branch of a fallen tree and became seriously ill again. He was then quickly escorted to Monte Cassino to convalesce.^[39] After resting for a while, he set out again, but stopped at the Cistercian Fossanova Abbey after again falling ill.^[42] The monks nursed him for several days, and as he received his last rites he prayed: "I receive Thee, ransom of my soul. For love of Thee have I studied and kept vigil, toiled, preached and taught..."^[43] He died on 7 March 1274^[42] while giving commentary on the Song of Songs.^[44]

Condemnation of 1277[link]

In 1277, the same bishop of France, Etienne Tempier, who had issued the condemnation of 1270 issued another, more extensive condemnation. One aim of this condemnation was to clarify that God's absolute power transcended any principles of logic that Aristotle or Averroes might place on it.^[45] More specifically, it contained a list of 219 propositions that the bishop had determined to violate the omnipotence of God, and included in this list were twenty Thomistic propositions. Their inclusion badly damaged Thomas's reputation for many years.^[46]

In The Divine Comedy, Dante sees the glorified spirit of Thomas in the Heaven of the Sun with the other great exemplars of religious wisdom.^[47] Dante asserts that Thomas died by poisoning, on the order of Charles of Anjou;^[48] Villani (ix. 218) cites this belief, and the Anonimo Fiorentino describes the crime and its motive. But the historian Ludovico Antonio Muratori reproduces the account made by one of Thomas's friends, and this version of the story gives no hint of foul play.^[49]

Thomas's theology had begun its rise to prestige. Two centuries later, in 1567, Pope Pius V proclaimed St. Thomas Aquinas a Doctor of the Church and ranked his feast with those of the four great Latin fathers: Ambrose, Augustine of Hippo, 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 Church. Even though Duns Scotus was more consulted at the Council of Trent, Thomas had the honor of having his Summa Theologica placed on the altar alongside the Bible and the Decretals.^[46][50]

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

Canonization[link]

When the devil's advocate at his canonization process objected that there were no miracles, one of the cardinals answered, "Tot miraculis, quot articulis"—"there are as many miracles (in his life) as articles (in his Summa)," viz., thousands.^[50] Fifty years after the death of Thomas, on 18 July 1323, Pope John XXII, seated in Avignon, pronounced Thomas a saint.^[51]

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 Basilique de Saint-Sernin, Toulouse. In 1974, they were returned to the Church of the Jacobins, where they have remained ever since.

In the General Roman Calendar of 1962, in the Roman Catholic Church, Thomas was commemorated on 7 March, the day of death. However, in the General Roman Calendar of 1969, Thomas's memorial was transferred to 28 January, the date of the translation of his relics to Toulouse.^[52]

Saint Thomas Aquinas is honored with a feast day on the liturgical of the Episcopal Church in the United States of America on 28 January.

Philosophy[link]

Part of a series on
St. Thomas Aquinas
Thomism Scholasticism negative theology divine simplicity Quinquae viae Beatific vision Actus purus Sacraments correspondence theory of truth hylomorphism substance theory (Ousia) accident substantial form quiddity (essence / nature) peripatetic axiom principle of double effect cardinal virtues theological virtues intellectual virtues natural law Just War just price concupiscence
Works Summa Theologica Summa contra Gentiles Contra Errores Graecorum Commentaries on Aristotle
Influences and people Aristotle ("The Philosopher") St. Paul ("The Apostle") Pseudo-Dionysius St. Augustine ("The Theologian") St. Boethius Avicenna Peter Lombard ("The Master") Averroes ("The Commentator") Maimonides ("Rabbi Moses") St. Albertus Magnus Reginald of Piperno
Related Pange Lingua Aristotelianism Dominican Order School of Salamanca Catholic theology Doctor of the Church Empiricism Neo-Thomism Æterni Patris
Philosophy Portal Catholicism Portal
v t e

Thomas was a theologian and a Scholastic philosopher.^[53] However, he never considered himself a philosopher, and criticized philosophers, whom he saw as pagans, for always "falling short of the true and proper wisdom to be found in Christian revelation."^[54] With this in mind, Thomas did have respect for Aristotle, so much so that in the Summa, he often cites Aristotle simply as "the Philosopher." Much of his work bears upon philosophical topics, and in this sense may be characterized as philosophical. Thomas's philosophical thought has exerted enormous influence on subsequent Christian theology, especially that of the Roman Catholic Church, extending to Western philosophy in general. Thomas stands as a vehicle and modifier of Aristotelianism and Neoplatonism.

Commentaries on Aristotle[link]

Thomas wrote several important commentaries on Aristotle, including On the Soul, Nicomachean Ethics and Metaphysics. His work is associated with William of Moerbeke's translations of Aristotle from Greek into Latin.

Epistemology[link]

Thomas believed "that for the knowledge of any truth whatsoever man needs divine help, that the intellect may be moved by God to its act."^[55] 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 such (truths) as pertain to faith."^[56] But this is the light that is given to man by God according to man's nature: "Now every form bestowed on created things by God has power for a determined act, which it can bring about in proportion to its own proper endowment; and beyond which it is powerless, except by a superadded form, as water can only heat when heated by the fire. And thus the human understanding has a form, viz. intelligible light, which of itself is sufficient for knowing certain intelligible things, viz. those we can come to know through the senses. "^[57]

Ethics[link]

Thomas's ethics are based on the concept of "first principles of action."^[58] 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.^[59]

Thomas 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 somewhat 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.^[60]

Furthermore, Thomas 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.^[61] 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 . . .^[62]

The desires to live and to procreate are counted by Thomas among those basic (natural) human values on which all human values are based. According to Thomas, all human tendencies are geared towards real human goods. In this case, the human nature in question is marriage, the total gift of oneself to another that ensures a family for children and a future for mankind.^[63]

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

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

Thomas 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."^[64]

Thomas contributed to economic thought as an aspect of ethics and justice. He dealt with the concept of a just price, normally its market price or a regulated price sufficient to cover seller costs of production. He argued it was immoral for sellers to raise their prices simply because buyers were in pressing need for a product.^[65][66]

Intentionality[link]

The pioneer of neurodynamics, cognitive neuroscientist Walter Freeman, considers the work of Thomas important in remodeling intentionality, the directedness of the mind toward what it is aware of. 

Psychology[link]

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (September 2011)

Aquinas maintains that a human is a single material substance. He understands the soul as the form of the body, which makes a human being the composite of the two. Thus, only living, form-matter composites can truly be called human; dead bodies are “human” only analogously. One actually existing substance comes from body and soul. A human is a single material substance, but still should be understood as having an immaterial soul, which continues after bodily death.

Ultimately, humans are animals; the animal genus is body; body is material substance. When embodied, a human person is an “individual substance in the category rational animal.”^[67] The body belongs to the essence of a human being. In his Summa Theologica, Aquinas clearly states his position on the nature of the soul; defining it as “the first principle of life.”^[68] The soul is not corporeal, or a body; it is the act of a body. Because the intellect is incorporeal, it does not use the bodily organs, as “the operation of anything follows the mode of its being.”^[69]

The human soul is perfected in the body, but does not depend on the body, because part of its nature is spiritual. In this way, the soul differs from other forms, which are only found in matter, and thus depend on matter. The soul, as form of the body, does not depend on matter in this way.

The soul is not matter, not even incorporeal or spiritual matter. If it were, it would not be able to understand universals, which are immaterial. A receiver receives things according to the receiver’s own nature, so in order for soul (receiver) to understand (receive) universals, it must have the same nature as universals. Yet, any substance that understands universals may not be a matter-form composite. So, humans have rational souls which are abstract forms independent of the body. But a human being is one existing, single material substance which comes from body and soul: that is what Thomas means when he writes that “something one in nature can be formed from an intellectual substance and a body,” and “a thing one in nature does not result from two permanent entities unless one has the character of substantial form and the other of matter.”^[70]

The soul is a "substantial form"; it is a part of a substance, but it is not a substance by itself. Nevertheless, the soul exists separately from the body, and continues, after death, in many of the capacities we think of as human. Substantial form is what makes a thing a member of the species to which it belongs, and substantial form is also the structure or configuration that provides the object with the abilities that make the object what it is. For humans, those abilities are those of the rational animal.

These distinctions can be better understood in the light of Aquinas’ understanding of matter and form, a hylomorphic ("matter/form") theory derived from Aristotle. In any given substance, matter and form are necessarily united, and each is a necessary aspect of that substance. However, they are conceptually separable. Matter represents what is changeable about the substance – what is potentially something else. For example, bronze matter is potentially a statue, or also potentially a cymbal. Matter must be understood as the matter of something. In contrast, form is what determines some particular chunk of matter to be a specific substance and no other. When Aquinas says that the human body is only partly composed of matter, he means the material body is only potentially a human being. The soul is what actualizes that potential into an existing human being. Consequently, the fact that a human body is live human tissue entails that a human soul is wholly present in each part of the human.

Theology[link]

17th century sculpture of Thomas Aquinas

Thomas viewed theology, or the sacred doctrine, as a science,^[38] 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. Thomas believed both were necessary — or, rather, that the confluence of both was necessary — for one to obtain true knowledge of God. Thomas blended Greek philosophy and Christian doctrine by suggesting that rational thinking and the study of nature, like revelation, were valid ways to understand truths pertaining to God. According to Thomas, God reveals himself through nature, so to study nature is to study God. The ultimate goals of theology, in Thomas's mind, are to use reason to grasp the truth about God and to experience salvation through that truth.

Revelation[link]

Thomas believed that truth is known through reason (natural revelation) and faith (supernatural revelation). Supernatural revelation has its origin in the inspiration of the Holy Spirit and is made available through the teaching of the prophets, summed up in Holy Scripture, and transmitted by 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 ways to know 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 (such as the Trinity). In Thomas'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 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.

Creation[link]

As a Catholic, Thomas believed that God is the "maker of heaven and earth, of all that is visible and invisible." Like Aristotle, Thomas posited that life could form from non-living material or plant life, a theory of ongoing abiogenesis known as spontaneous generation:

Since the generation of one thing is the corruption of another, it was not incompatible with the first formation of things, that from the corruption of the less perfect the more perfect should be generated. Hence animals generated from the corruption of inanimate things, or of plants, may have been generated then.^[71]

Additionally, Thomas considered Empedocles' theory that various mutated species emerged at the dawn of Creation. Thomas reasoned that these species were generated through mutations in animal sperm, and argued that they were not unintended by nature; rather, such species were simply not intended for perpetual existence. This discussion is found in his commentary on Aristotle's Physics:

The same thing is true of those substances which Empedocles said were produced at the beginning of the world, such as the ‘ox-progeny’, i.e., half ox and half man. For if such things were not able to arrive at some end and final state of nature so that they would be preserved in existence, this was not because nature did not intend this [a final state], but because they were not capable of being preserved. For they were not generated according to nature, but by the corruption of some natural principle, as it now also happens that some monstrous offspring are generated because of the corruption of seed.^[72]

Just war[link]

Augustine of Hippo agreed strongly with the conventional wisdom of the time, that Christians should be pacifists in their personal lives. But he routinely argued that this did not apply to the defence of innocents. In essence, the pursuit of peace must include the option of fighting to preserve it in the long-term.^[73] Such a war could not be preemptive, but defensive, to restore peace.^[74]

Thomas Aquinas, centuries later, used the authority of Augustine's arguments in an attempt to define the conditions under which a war could be just:^[75]

• First, war must occur for a good and just purpose rather than for self-gain or as an exercise of power.
• Second, just war must be waged by a properly instituted authority such as the state.
• Third, peace must be a central motive even in the midst of violence.^[76]

Nature of God[link]

Thomas believed that the existence of God is self evident in itself, but not to us. "Therefore I say that this proposition, "God exists," of itself is self-evident, for the predicate is the same as the subject.... Now because we do not know the essence of God, the proposition is not self-evident to us; but needs to be demonstrated by things that are more known to us, though less known in their nature — namely, by effects."^[77]

Thomas believed that the existence of God can be proven. In the Summa Theologica, he considered in great detail five reasons for the existence of God. These are widely known as the quinque viae, or the "Five Ways."

The Five Ways Philosophers Have Proven God's Existence

1. Change: Some things are undoubtedly undergoing change, though cannot cause their own change. Since Thomas believed there can be no infinite chain of causes of change, this leads to the conclusion there must be a first cause of changing that is not itself changed by anything else, and this is what everyone understands by God.
2. Causation: Like change, nothing can cause itself, and like change there must be a First Cause, called God
3. Existence of necessary and the unnecessary: Our experience includes things certainly existing but apparently unnecessary. Not everything can be unnecessary, for then once there was nothing and there would still be nothing. Therefore, we are compelled to suppose something that exists necessarily, having this necessity only from itself; in fact itself the cause why other things exist.
4. Gradation: If we can notice a gradation in things in the sense that some things are more hot, good, etc., there must be a superlative which is the truest and noblest thing, and so most fully existing. This then, we call God -->note Thomas does not ascribe actual qualities to God Himself!
5. Ordered tendencies of nature: A direction of actions to an end is noticed in all bodies following natural laws. Anything without awareness tends to a goal under the guidance of one who is aware. This we call God --> Note that even when we guide objects, in Thomas' view the source of all our knowledge comes from God as well.^[78]

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

1. God is simple, without composition of parts, such as body and soul, or matter and form.^[79]
2. God is perfect, lacking nothing. That is, God is distinguished from other beings on account of God's complete actuality.^[80] Thomas defined God as the ‘Ipse Actus Essendi subsistens,’ subsisting act of being.^[81]
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.^[82]
4. God is immutable, incapable of change on the levels of God's essence and character.^[83]
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 Thomas's words, "in itself the proposition 'God exists' is necessarily true, for in it subject and predicate are the same."^[84]

In this approach, he is following, among others, the Jewish philosopher Maimonides.^[85]

Following St. Augustine of Hippo, Thomas defines sin as "a word, deed, or desire, contrary to the eternal law."^[86] It is important to note the analogous nature of law in Thomas's legal philosophy. Natural law is an instance or instantiation of eternal law. Because natural law is that which human beings determine according to their own nature (as rational beings), disobeying reason is disobeying natural law and eternal law. Thus eternal law is logically prior to reception of either "natural law" (that determined by reason) or "divine law" (that found in the Old and New Testaments). In other words, God's will extends to both reason and revelation. Sin is abrogating either one's own reason, on the one hand, or revelation on the other, and is synonymous with "evil" (privation of good, or privatio boni^[87]). Thomas, like all Scholastics, generally argued that the findings of reason and data of revelation cannot conflict, so both are a guide to God's will for human beings.

Nature of the Trinity[link]

Thomas 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. Thomas wrote that the term "Trinity" "does not mean the relations themselves of the Persons, but rather the number of persons related to each other; and hence it is that the word in itself does not express regard to another."^[88] 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 give grace 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 within those who have experienced salvation by God; according to Aidan Nichols. ^[89]

Prima causa – first cause[link]

Thomas's five proofs for the existence of God take some of Aristotle's assertions concerning principles of being. For Thomas, God as prima causa (first cause) comes from Aristotle's concept of the unmoved mover and asserts that God is the ultimate cause of all things.^[90]

Nature of Jesus Christ[link]

In the Summa Theologica, Thomas 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."^[91] Thomas argued in favor of the satisfaction view of atonement; that is, that Jesus Christ died "to satisfy for the whole human race, which was sentenced to die on account of sin."^[92]