Summa Theologica Part I (Prima Pars) Thomas Aquinas - The Summa Theologiae (Latin: Compendium of Theology or Theological Compendium; also subsequently called the Summa Theologica or simply the Summa, written 1265-1274) is the best-known work of Thomas Aquinas (c.1225-1274), and although unfinished, "one of the classics of the history of philosophy and one of the most influential works of Western literature." It is intended as a manual for beginners in theology and a compendium of all of the main theological teachings of the Church. It presents the reasoning for almost all points of Christian theology in the West. The Summa's topics follow a cycle: the existence of God; Creation, Man; Man's purpose; Christ; the Sacraments; and back to God. (courtesy of wikipedia.com).

This is part 1, 'Prima Pars'.

Aquinas's greatest work was the Summa, and it is the fullest presentation of his views. He worked on it from the time of Clement IV (after 1265) until the end of his life. When he died, he had reached Question 90 of Part III (on the subject of penance). What was lacking was added afterwards from the fourth book of his commentary on the Sentences of Peter Lombard as a supplementum, which is not found in manuscripts of the thirteenth and fourteenth centuries. The Summa was translated into Greek (apparently by Maximus Planudes around 1327), Armenian, many European languages, and Chinese.

It consists of three parts. Part I treats of God, who is the "first cause, himself uncaused" (primum movens immobile) and as such existent only in act (actu) - that is, pure actuality without potentiality, and therefore without corporeality. His essence is actus purus et perfectus. This follows from the fivefold proof for the existence of God; namely, there must be a first mover, unmoved, a first cause in the chain of causes, an absolutely necessary being, an absolutely perfect being, and a rational designer.

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Thomas Aquinas (sometimes styled Thomas of Aquin or Aquino), was a Dominican friar and priest notable as a scholastic theologian and philosopher. He is honored as a saint and "Doctor of the Church" in the Roman Catholic tradition.

Aquinas lived at a critical juncture of western culture when the arrival of the Aristotelian corpus in Latin translation reopened the question of the relation between faith and reason, calling into question the modus vivendi that had obtained for centuries. This crisis flared up just as universities were being founded. Thomas, after early studies at Montecassino, moved on to the University of Naples, where he met members of the new Dominican Order. It was at Naples too that Thomas had his first extended contact with the new learning. When he joined the Dominican Order he went north to study with Albertus Magnus, author of a paraphrase of the Aristotelian corpus. Thomas completed his studies at the University of Paris, which had been formed out of the monastic schools on the Left Bank and the cathedral school at Notre Dame. In two stints as a regent master Thomas defended the mendicant orders and, of greater historical importance, countered both the Averroistic interpretations of Aristotle and the Franciscan tendency to reject Greek philosophy. The result was a new modus vivendi between faith and philosophy which survived until the rise of the new physics. The Catholic Church has over the centuries regularly and consistently reaffirmed the central importance of Thomas's work for understanding its teachings concerning the Christian revelation, and his close textual commentaries on Aristotle represent a cultural resource which is now receiving increased recognition.