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Abortion, conception, and ‘ensoulment’: What’s a Catholic supposed to believe?

Last week, Washington’s Cardinal Wilton Gregory spoke the National Press Club, during which he fielded questions about President Joe Biden’s support for abortion.

“The Catholic Church teaches and has taught that life -- human life -- begins at conception. So the president is not demonstrating Catholic teaching in that,” Gregory said. 

“Among the theologians, there's all kinds of medical issues about when does conception take place,” the cardinal added. “Is it at implantation? Is it at some point when the sperm and the ovum come together and create a new reality? And theologians have debated that and continue to debate that.”


Most Catholics tend to understand conception as the moment of fertilization, when an individual genetic human life forms. But what does the Church actually teach? Is there debate about when conception takes place? And what does it mean for how Catholics talk about life issues?

To understand the details, The Pillar spoke to Dr. John Brehany, vice-president of the National Catholic Bioethics Center. Here’s what he told us:

Cardinal Gregory mentioned that theologians debate when conception happens — what is this debate all about?

Perhaps Cardinal Gregory's choice of words was not precise enough to capture what has been a real debate in the Church over the centuries. The issue debated was not the timing of "conception" per se, although knowledge about the biological details of conception grew over time, especially with the invention and application of the microscope. 

Everyone understood that a new human life came into being after human sexual intercourse, but a key question which received different answers at different times was: "When does that new human life receive a human soul?" 

Prior to the 20th century, the early apologists, Church Fathers, councils, and, eventually, theologians, made statements or teachings or arguments that addressed the issue of ensoulment. All of these statements were influenced by particular understandings of the proper interpretation of key passages of Scripture, their state of knowledge of biology, etc., and the philosophical framework they accepted. 

For example, Aquinas was influenced in part by Aristotle's hylemorphism [which defines “being” as the combination of matter and form] and so, as a matter of reasoning about human development, he held for a theory of delayed human ensoulment. 

Academic support for “delayed animation” was significantly rejected by the end of the 1600s, and by the late 19th century there was a great amount of new scientific evidence which ended meaningful debate about “delayed ensoulment.” At that time, Pope Pius XI removed the distinction in canon law between penalties for pre- and post-quickening abortions, and it was the American Medical Association that led the charge against abortion, significantlly based on the same scientific evidence. 

Some philosophical debate arose in the early 1970s when the philosopher Joseph Donceel argued that Aquinas's theory of delayed ensoulment made more sense in light of recent scientific findings. His position was not convincing to many. 

More influentially — and wrongly — the dissident moral theologian Richard McCormick SJ helped to advance debate about the moral status of the embryo based on the phenomenon of human twinning, and came up with a new term “pre-embryo,” but that term and distinction has not been accepted even by secular biologists.

It is important to recognize that, in all the debates about when human ensoulment takes place and what canonical penalties would apply to someone pursuing or causing an abortion at a given stage of human development, all reputable leaders and theologians in the history of the Church have always taught that abortion is a form of homicide and a serious sin. 

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Has the Church’s magisterium taken a definitive position on when “conception” or “ensoulment” happens? 

The Church has noted, but has not tried to settle, the debate about the nature and timing of human ensoulment. That human life begins at conception is not a matter of faith or doctrinal definition but of the evidence of our senses and science.

The [Congregation for the Doctrine of the Faith’s 1974] Declaration on Procured Abortion references the debate about ensoulment and notes it is a philosophical debate:

“From the time that the ovum is fertilized, a new life is begun which is neither that of the father nor of the mother; it is rather the life of a new human being with his own growth. It would never be made human if it were not human already.”

“To this perpetual evidence ... modern genetic science brings valuable confirmation. It has demonstrated that, from the first instant, the programme is fixed as to what this living being will be: a man, this individual-man with his characteristic aspects already well determined. Right from fertilization is begun the adventure of a human life, and each of its great capacities requires time ... to find its place and to be in a position to act.”

The [1987 Instruction on respect for human life in its origins] Donum vitae references this same teaching and expands on the debate about ensoulment more explicitly:

“This teaching [of the 1974 document] remains valid and is further confirmed, if confirmation were needed, by recent findings of human biological science which recognize that in the zygote resulting from fertilization, the biological identity of a new human individual is already constituted,” it said.

“Certainly no experimental datum can be in itself sufficient to bring us to the recognition of a spiritual soul; nevertheless, the conclusions of science regarding the human embryo provide a valuable indication for discerning by the use of reason a personal presence at the moment of this first appearance of a human life: how could a human individual not be a human person?” 

“Thus the fruit of human generation, from the first moment of its existence, that is to say from the moment the zygote has formed, demands the unconditional respect that is morally due to the human being in his bodily and spiritual totality.”

“The human being is to be respected and treated as a person from the moment of conception; and therefore from that same moment his rights as a person must be recognized, among which in the first place is the inviolable right of every innocent human being to life,” said the CDF in its instruction.  

Again, the Church does not attempt to settle the issue doctrinally. However, it teaches that scientific evidence supports the reasoned conclusion that a human individual with a personal presence is present at or after conception and that each human individual should be treated as a person from the first moment of existence.

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So, what are Catholics required to believe about when human life begins?

When life begins is not a matter of belief per se; it is a matter of biology and human reason which can rise to the level of scientific knowledge. 

A new human life, by its very nature, is in need of love and support from the very beginning. Therefore, Catholics should believe and follow those teachings of the Church that call for respect for human life from its origins and should believe that abortion is always an abominable crime and should never be chosen or accepted.

Catholics should take care not to believe the myths and lies that are produced by those influential individuals and institutions that want to confuse people about the true nature of abortion or who wish to exploit the bodies and lives of unborn children. 

For example, the myth that "pregnancy begins at implantation” is a deception that has caused misunderstandings for decades. 

For the entire moral tradition of the Church, despite differences in time, philosophical theory, and medical science, the Church has taught, and Catholics have believed, that abortion always is a form of homicide. 

Theologians, pastors, canonists, and popes have differed on the meaning and timing of human ensoulment, and on issues like what type of penance or penalties should be applied to those who pursue or cause abortion depending on the person’s state of knowledge or freedom and the unborn child's state of development, and also on knotty ethical dilemmas such as what one could do to save the life of a pregnant woman in distress.

But they have all held, with amazing consistency, that abortion at any point is a serious sin, a type of homicide, and should not be done.

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