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St. Thomas Aquinas (1225-1274) "The Angelic Doctor" was a 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 Calvin or 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 works Summa Theologica gives humanity a child like 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 Masters degree at the University of Paris, the year 1245.