St. Thomas Aquinas (1225-1274) "The Angelic Doctor" was an Italian Dominican friar who wrote Summa Theologica. Many consider this to be the most perfect and complete summary of Christian theology, and he established an entire type of Christian philosophy known as "Thomism", which is followed to this day. Aquinas was somewhat controversial during his life, but was quickly revered by the Catholic Church after his death. Many of the controversies surrounding Aquinas stem from his synthesis of Aristotlean philosophy with Christian philosophy, causing him to break with many of the traditionally held philosophical and theological positions espoused by the dominant Augustinian synthesis of Neoplatonic philosophy and Christianity.
He developed five proofs for the existence of God using logic. The first three were "cosmological" proofs rather than the "ontological" approach of St. Anselm. A cosmological proof deals with the natural order of the universe. Aquinas' most famous cosmological argument was that whatever is in motion (for example, us) must have been put in motion by something else (our parents). They, in turn, must have been put in motion by something else (their parents). But this sequence cannot go on to infinity. There must have been a first mover. This we call "God".
Saint Thomas had a different view of the fall than those later developed by Calvin and Luther. He did not view man as totally depraved, but rather that his will was weakened and his intellect clouded. Nonetheless, his nature was not totally corrupted, for as created by God he remained essentially good. Nevertheless, man cannot attain salvation on his own, but is in need of grace. Though human intellect is imperfect, unassisted human reason can still understand many of the truths about God. For instance: the existence of God can be shown from the nature of the created universe. However, certain things are only knowable through Divine Revelation such as the doctrine of the Blessed Trinity. Because of his view of the power of the human mind, though harmed by the fall but not totally destroyed, the works of the classical, secular philosophers could be brought into the service of Christian theology. Charles Murray wrote, "Aquinas made the case, eventually adopted by the Church, that human intelligence is a gift from God, and that to apply human intelligence to understanding the world is not an affront to God but is pleasing to him." 
Saint Thomas wrote many theological and philosophical books and composed several beautiful hymns. Hailed as a masterpiece, his work Summa Theologica gives humanity a childlike revelation of God. The book was never completed, though it contains more than 2 million words. After a religious vision / experience, he stopped writing explaining, “All that I have written seems to me like straw compared to what has now been revealed to me.” He died three months later at the monastery of Fossanova, one mile from Sonnino, on March 7, 1274
The entire Summa provides simple and direct illuminations into the nature of God: "It can be proved in five ways that God exists."  The basic format of the arguments in the Summa begin with a few brief postulates about the nature of God followed by a series of reasonable objections to those assertions. A flaw in the logic of the objections is raised and the objections are systematically answered by logical counterarguments, bringing the argument to a conclusion supporting the original postulates.
Summa Theologica is divided into three parts and contains 27 questions:
The first part Prima Pars (God and what precedes from Him)
The second part Prima Secundae and Secunda Secundae (Law and Grace, Charity and Justice)
The third part Tertia Pars (Christ who as man is our way to God)
Concerning the nature of God, Aquinas found that 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."
St. Thomas Aquinas is further known for his famous observation that the Devil cannot withstand mockery.
July 18, 1323, Thomas Aquinas was canonized as a Saint by Pope John XXII at Avignon
In 1567, St. Thomas Aquinas received the title Doctor of the Church or 'Angelic Doctor'. In the 2000-year history of Christ, he is one of only 33 with that designation.
Early in Life
As a young child, his parents sent him to study at a monastery when five years old.
Thomas studied and earned his master's degree at the University of Paris, in the year 1245.
Some conservatives have argued that Thomas Aquinas was an important influence on the development of liberalism due to his optimism in human reason. The conservative Senator John Porter East, a former professor of political philosophy, wrote:
"To put the matter bluntly, modern liberal Catholicism, and its non-Catholic associates, have preferred Aquinas over Augustine. Leo XIII set the tone in Aeterni Patris. He acknowledged the greatness of Augustine, but indicated that this early Saint is a stepping stone on the way to the summit, which is Aquinas. As Aquinas showed that faith and reason are compatible, the Pope contended his philosophy would serve as a bridgebuilder to the secular rationalist. Aquinas’ reliance upon “reason” has great appeal to modern liberals; however, the matter broadens beyond that, for Aquinas leads to Aristotle, while Augustine points to Plato, and within liberal thinking the former two are preferred."
Richard M. Weaver in Ideas Have Consequences, argued that Thomas Aquinas' imposition of Aristotle on the Roman Catholic Church caused the church to turn away from rigorous morality and to accept pragmatic acquiescence to the world.
The Christian apologist and philosopher Francis Schaeffer offered a similar indictment on Thomas Aquinas in Escape from Reason. Schaeffer argued that Aquinas "separated nature from grace," and allowed for the study of the earthly realm to be entirely removed from the study of Christianity. In doing so, he "laid the groundwork for the Humanistic Renaissance" and the "autonomous individual." Schaeffer reprimanded Aquinas for his belief in the intrinsic goodness of man—a radically unconservative persuasion. Aquinas believed that, though the will was affected by the fall, the intellect was not. Thus, reasoning and philosophy became free to be pursued without subjugation to the limitations of the Scriptures and divine revelation. Schaeffer viewed Aquinas as one of the founding fathers of liberal modernity, accrediting to him some responsibility for the Renaissance and the Enlightenment. In Schaeffer's words, "...Aquinas had opened the way to an autonomous Humanism, an autonomous philosophy, and once the movement gained momentum, there was soon a flood."
Unlike many conservatives, Thomas Aquinas did not strenuously uphold the intrinsic merit of property rights and the Biblical prohibition on theft. Of theft, he wrote that "It is not theft, properly speaking, to take secretly and use another's property in a case of extreme need: Because that which he takes for the support of his life becomes his own property by reason of that need." In another statement foreshadowing later socialist arguments, Aquinas claimed that "In cases of need all things are common property, so that there would seem to be no sin in taking another's property, for need has made it common."
However, Thomas Aquinas did uphold conservative views on other issues, he supported the use of capital punishment. He wrote, "Therefore if a man be dangerous and infectious to the community, on account of some sin, it is praiseworthy and advantageous that he be killed in order to safeguard the common good" . . . . ST IIa-IIae, q. 64, a. 2.
"It is permissible to kill a criminal if this is necessary for the welfare of the whole community. However, this right belongs only to the one entrusted with the care of the whole community -- just as a doctor may cut off an infected limb, since he has been entrusted with the care of the health of the whole body." ST IIa-IIae, q. 64, a. 3. 
He wrote that war was justifiable: "Those who wage war justly aim at peace, and so they are not opposed to peace, except to the evil peace, which Our Lord "came not to send upon earth" (Matthew 10:34). Hence Augustine says (Ep. ad Bonif. clxxxix): "We do not seek peace in order to be at war, but we go to war that we may have peace. Be peaceful, therefore, in warring, so that you may vanquish those whom you war against, and bring them to the prosperity of peace." 
He wrote that people have a right to private property: "Human affairs are conducted in more orderly fashion if each man is charged with taking care of some particular thing himself, whereas there would be confusion if everyone had to look after any one thing indeterminately." 
He wrote that according to natural law a marriage can only be between a man and a woman and that sex outside of marriage is a sin: "This union with a certain definite woman is called matrimony; which for the above reason is said to belong to the natural law. Since, however, the union of the sexes is directed to the common good of the whole human race, and common goods depend on the law for their determination, as stated above (FS, Question , Article ), it follows that this union of man and woman, which is called matrimony, is determined by some law. What this determination is for us will be stated in the Third Part of this work (XP, Question , seq.), where we shall treat of the sacrament of matrimony. Wherefore, since fornication is an indeterminate union of the sexes, as something incompatible with matrimony, it is opposed to the good of the child's upbringing, and consequently it is a mortal sin." 
He wrote a defense that would support the "Stand Your Ground" laws that many Liberals object to: "Accordingly the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in "being," as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists [Cap. Significasti, De Homicid. volunt. vel casual.], "it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense."
In Dante's Paradiso, Thomas Aquinas appears in the Heaven of the Sun, alongside other great thinkers including King Solomon. There, he and the other learned men move in a heavenly dance - a slightly incongruous image given that Aquinas was famously corpulent in life, earning the somewhat irreverent nickname "the Ox of God."
- Second Chance for Thomas Religion-Online.org
- , Philosophy of Religion- Historic Figures
- , Saint Thomas Aquinas Biography
- John P. East, “The Political Relevance of St. Augustine,” Modern Age 16 (Spring, 1972), 168.
- Richard M. Weaver, Ideas Have Consequences (Chicago: University of Chicago Press, 1948), 119.
- Francis Schaeffer, Escape from Reason (Downers Grove, IL: InterVarsity Press, 1968), 9-18.
- Faith and Liberty: The Economic Thought of the Late Scholastics
- Culture's Bell Curve - a review of Charles Murray's Human Accomplishment
- Thomas Aquinas quotes
- Works by St. Thomas Aquinas - text and free audio - LibriVox