The following was written by Frank K. Flinn, Ph.D., adjunct professor of religious studies in Arts & Sciences and author of the Encyclopdia of Catholicism (2007).
Democratic vice presidential candidate Joseph Biden is telling the Catholics in his audiences that St. Thomas Aquinas had a different teaching on abortion than the current pope and his immediate predecessors. Many Catholics are saying, "He simply cannot be right." Well, the short answer is: Biden is right. The news media are saying that American bishops are giving him a theology lesson on abortion. Mr. Biden is in a position to give them one right back.
The Catholic teaching on abortion has complex roots in Jewish teaching, Greek thought and early Christian doctrine. Jewish teaching shows great reverence for life as a gift from God. The law of compensation in Exodus 21:22 makes a distinction between the penalty for striking a pregnant woman that ends in the loss of the fetus (a monetary amount) or the mother (death).
The Greek Septuagint text of this verse shows the influence of Greek thought. It distinguishes between incompletely and completely formed fetuses, and exacts a penalty of death in the case of the abortion of the latter. This is a clear reference to Aristotle's distinction between three types of souls corresponding to three types of living beings: plants, animals and humans. Aristotle taught that the human fetus does not receive a human soul until it takes on a human form. This became known as the delayed hominization thesis or the late implanting of the human soul.
Greeks and Romans were not squeamish about abortion. They held the state to be supreme and abortion was permissible if political reasons dictate. Thus they freely used drugs causing abortions and exposed defective children, even normal female children if a male heir was desired first.
Like their Jewish contemporaries, second century Christian communities rejected abortion. Many early Christian writings, like the Didache and the Epistle to Barnabas, preach against abortion. Several early local councils of bishops condemned abortion which they thought was closely linked with adultery. Augustine, however, affirmed the Aristotelian teaching in his Commentary on Exodus and stated that he did not have an answer about the status of a fetus.
The abortion question entered into a new phase during the Middle Ages. St. Anselm of Canterbury gave the most forceful statement in favor of the delayed hominization thesis: "No human intellect accepts the view that an infant has the rational soul from the moment of conception." St. Thomas Aquinas also accepted Aristotle's theory of the late appearance of the human soul in the fetus. He taught that the abortion of a fetus before it has the human soul is a sin against marriage but that it is not murder. The famous medieval jurist Gratian wrote, "He is not a murderer who brings about abortion before the soul is in the body."
It is important to note that for roughly 500 years the Catholic church followed the teaching of Aristotle and St. Thomas on the status of the fetus. The Council of Vienne (1312) under Pope Clement V affirmed Aristotle's teaching on delayed hominization. But in 1588 Sixtus V issued the bull Effraenatum excommunicating anyone who used contraception and induced abortion at any time. Three years later Gregory XIV rescinded the severity of Sixtus' punishments and reinstated the doctrine of delayed hominization or "quickening" of the fetus, approximately sixteen weeks after conception. This rule remained in effect for another three hundred years until 1869 when Pope Pius IX imposed automatic excommunication for abortion at any stage of pregnancy. Implicitly Pius's teaching embraced a theory of the immediate implanting of the soul at the moment of conception.
This last position was reaffirmed at the Second Vatican Council in 1962. In 1987, the Congregation for the Doctrine of the Faith issued an instruction called DonumVitae which said that a fertilized egg would become nothing other than a human being. However, the earlier instruction Declaration on Procured Abortion (1974) expressly left aside the question of the moment when the spiritual soul is infused. Many thought that Donum Vitae slammed the door on Aristotle's and Aquinas's position on the fetus.
Since Donum Vitae several Catholic moral theologians have noted that the fertilized egg at the blastosphere stage is not a physical individual until it is restricted by implantation in the wall of the uterus. This does not happen for about two weeks after fertilization. The early cell group can split into twins, etc., or split and be reabsorbed by the original set of cells. This argues for delayed ensoulment like Aristotle's. Those who uphold the immediate infusion of the soul at conception are forced into the rather irrational position of having God infuse billions of souls at conception and then immediately discarding the cells that bear them.
In Humanae Vitae (1968) Pope Paul VI condemned direct therapeutic abortion. Contrary to popular misconceptions even on the part of many priests and maybe a few bishops, Catholicism does allow for indirect abortions, that is, abortions which aim not directly at the fetus but at the removal of a diseased or endangering condition: a cancerous uterus, an ektopic pregnancy in the fallopian tube, etc. The moral reasoning is based on the principle of double effect: in seeking the good result a bad result may be indirectly tolerated.
Today the Roman Catholic Church often likes to promote the theory that its teachings on abortion are eternal. The history of the abortion controversy clearly demonstrates that this theory cannot be true. Whether a Catholic agrees with Joe Biden or not, he is still right about St. Thomas Aquinas and many other authoritative teachers of Catholic doctrine in the past, including popes. Both the current papacy and the American episcopacy themselves stand in need of a lesson in Catholic doctrinal history.