St. Thomas Aquinas (c. 1225-1274)

By: Katherine Brind'Amour

St. Thomas Aquinas

Widely known as a key contributor to the Roman Catholic Church’s body of doctrine, St. Thomas Aquinas also published an opinion on the moral status of embryos and fetuses that seems contradictory to the Catholic Church's current standpoint on the matter. Born in Naples, Italy, around 1225 (scholars debate the exact year of many of his life events) to wealthy nobility, Thomas Aquinas quickly proved himself a pious and astute scholar with an insatiable desire for logic and understanding. After receiving his formative education in Montecassino and Naples, Italy, Aquinas joined the order of the Dominicans. His desire for the holy life shocked and upset his family, who lamented his choice of a poor lifestyle devoted to service. To prevent Aquinas from following through with his plan, his family held him captive in the San Giovanni fortress in Rocca Secca, Italy, for nearly two years. After his mother and siblings noted his devotion to the Church evidenced by his daily studies and constant writing (not to mention his dismissal of concubines), they relented and allowed him to take his vows with the Dominicans around 1245. It is also estimated that he officially received his Master’s in the Arts from the University of Naples around this time.

Immediately thereafter, Aquinas was sent to Paris to study under Albertus Magnus, a famous Dominican scientist, theologian, and philosopher. In 1248 the pair traveled to Cologne, Italy, where Aquinas began to teach under Magnus as a Bachelor professor. Because of his strong work in Cologne, the archbishop Conrad of Hochstaden elevated Aquinas to the priesthood in 1250. Soon after, Aquinas was transferred to the Dominican studium in Paris to continue serving as a Bachelor professor. His hard work and pious teachings quickly caught the attention of his superiors, and Aquinas was ordered to prepare for a Doctorate in Theology from the University of Paris, which he received in 1257.

The career of St. Thomas Aquinas following the receipt of his Doctorate was rather simple, as he dedicated himself to service, academics, and God. His skill for argument and preaching gained him extreme popularity among the public and the favoritism of the popes. He is described as having often experienced moments of ecstasy and visions, mainly during celebration of mass, and his influence in the Church was widespread during his lifetime. Pope Clement IV appointed Aquinas as Archbishop of Naples in 1265, but Aquinas begged to be able to remain a traveling teacher and writer. Upon release from the appointment, he dedicated himself to his principal work, Summa Theologica, which was to serve as a comprehensive defense of Christian truth.

Summa Theologica delineates St. Thomas Aquinas’s opinion on the moral status of the embryo or fetus and the act of abortion. His discussion of sin, morality, and murder indicates his views on the development of life within the womb. These sections show that Aquinas believed in the progression of life from a “vegetable”-like, unanimated state to an animal life and finally to a human, animated state. Summa Theologica offers no defense of abortion as a permissible act at any stage in the pregnancy, but it does specify that once the fetus has become animated (when he believed ensoulment of the living human being took place), it is homicide to kill it. This measure of ensoulment or delayed hominization (the belief that the embryo or fetus was not a human life with a soul until a particular event after conception) is typically equated with the stage at which quickening took place—defined by Aristotle as forty days for boys and eighty days after conception for girls.

It is the concept of delayed hominization that seemingly pits these comments of St. Thomas Aquinas against the modern Roman Catholic Church; when it comes to ensoulment, the Church now defends the position that an embryo is infused with a human soul upon fertilization, making any intentionally procured abortion a sin of murder (because it kills a living being with a human soul). St. Thomas Aquinas’s opinion on abortion and fetal development receives much attention from people on both sides of the debate over abortion. Typically, pro-choice advocates claim that Aquinas’s position shows an inconsistency in Church belief throughout history on the topic and a defensible option for pro-choice Catholics, while pro-life advocates point out that Aquinas never discusses abortion as an acceptable option and furthermore would most likely not have maintained his delayed hominization theory had he been privy to the marvels of modern science.

Perhaps before he had a chance to clarify his writings on the matter, St. Thomas Aquinas declared he would write no more. On 6 December 1273 he reportedly experienced a long episode of ecstasy during Mass, and later said that such things had been revealed to him that his previous writings seemed nothing in comparison. He immediately began preparing himself for his death, which took place on 7 March 1274. Aquinas was canonized on 18 July 1323 by Pope John XXII. Pope Pius V declared him a Doctor of the Catholic Church in 1567 and his importance to Catholic Church doctrine was cemented during Pope Leo XIII’s reign, when St. Thomas Aquinas was celebrated in Aeterni Patris and named the patron of all Catholic educational institutions worldwide.


  1. Aquinas. Summa Theologica. Ed. Kevin Knight. “Summa Theologica.” Trans. Fathers of the English Dominican Province, 1920. (Accessed June 11, 2007).
  2. Kennedy, D. J. “St. Thomas Aquinas.” The Catholic Encyclopedia, Volume XIV. Transcribed by Kevin Cawley. New York: Robert Appleton Company, 1912. (Accessed April 25, 2007).
  3. McInerny, Ralph and John O’Callaghan. “Saint Thomas Aquinas.” The Stanford Encyclopedia of Philosophy (Spring 2005 Edition). Ed. by Edward N. Zalta. (Accessed September 28, 2007).



Jane Maienschein

How to cite

Brind'Amour, Katherine, "St. Thomas Aquinas (c. 1225-1274)". Embryo Project Encyclopedia ( ). ISSN: 1940-5030


Arizona State University. School of Life Sciences. Center for Biology and Society. Embryo Project Encyclopedia.

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Monday, September 11, 2023 - 10:58

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