From Aristotle to Aquinas: Ancient & Medieval Perspectives on Abortion


With the recent overturning of Roe v. Wade, the historical question of abortion remains a pertinent topic on the minds of many legal scholars. This article explores the historical record behind abortion, explaining the myriad of ways ancient and medieval philosophers pondered the question. Despite the relatively recent establishment of the right to privacy, it is revealed that diverging perspectives regarding abortion have influenced its current legal status in both Europe and the United States. Specifically, the philosophers Aristotle and Aquinas are to be analyzed for their definition of what exactly constitutes a person and at what specific point abortion involves the deliberate termination of a person.


Ancient Perspectives on Abortion

Though ancient perspectives on abortion were as varied and complex as many modern opinions, it is possible to glean a certain sense of continuity on the topic from philosophers of the time due to their belief that formed humans are capable of feeling physical sensations. Turning to the ancient Greek philosopher Aristotle, he makes a critical distinction between what he considers a formed and unformed fetus. The unformed fetus, defined by its biological sex and criteria of fetal movement, does not have the key characteristics of life and sensation (Dickison, 1973). Therefore, abortion is permitted for an unformed fetus. This dividing line between the lack of sensation and its presence is what distinguishes a formed from an unformed fetus, thus making abortion admissible up to a certain point in fetal development.

Figure 1: Raphael's Aristotle and Plato, School of Athens.

On the other hand, Stoic philosophers took a more concrete approach to determine the personhood of a fetus. According to the Stoics, a fetus is only designated as a living human post-birth, thereby granting mothers full permission to abort in all three trimesters (Dickison, 1973). Therefore, it is possible to view two diverging social perspectives on the permissibility of abortion: that of the Aristotelian division between formed and unformed, and the wide Stoic interpretation of life at birth.


Aristotelian metaphysics takes a step further in its designation, however. A key principle of Aristotle’s metaphysics is that of potentiality. This principle dictates that fetuses have the potential to become full human beings due to the qualities they already possess, such as anatomical features like organs. Many legal scholars have applied this argument to posit that abortion should not be allowed (Morgan, 2013). The principle of potentiality is encapsulated in one brief golden rule: “If it would be wrong to kill an adult human being because he has a certain property, it is wrong to kill an organism (e.g., a fetus) which will come to have that property if it develops naturally” (Hare, 1975, p. 209). Furthermore, Aristotle reasoned that tangible objects could not exist without their hypothetical potentials (Garrison, 2001). Therefore, all living things have an end goal to strive for, a tendency towards full attainment. Future philosophers, governments, and religious officials would cite Aristotle’s potentiality principle and the designation between formed and unformed fetus-hood for their own perspectives on abortion for centuries to come.



Figure 2: Marble plaque showing parturition scene, Ostia, Italy.

Medieval Christian Perspectives on Abortion

Christianity would struggle to come to terms with a concrete opinion on abortion for the first centuries of its existence. Grappling with the moral enshrinement of what constitutes a person and the inevitable fact that women can and do terminate pregnancies, the Church would have various positions on abortion seemingly different from its modern position. This article turns to the opinions of Thomas Aquinas, a prolific medieval philosopher whose positions on ethics and abortion have profoundly shaped Catholic theology. Specifically, Aquinas’ ruminations on the definition of personhood and the value of life found in the act of abortion are discussed.


Notably, the ancient and medieval view of conception involves menstrual fluid being guided under the influence of the father’s sperm to form a solidified being, similar to agricultural metaphors of planting ‘seeds’ (Haldane and Lee, 2003). This being would therefore evolve into a person to which a rational and thinking soul would later become infused. However, this process of ensoulment would take weeksspecifically, forty days after conception for a male and eighty days for a female (Brind'Amour, 2007). Remarkably similar to Aristotle’s earlier view regarding a formed and unformed fetus, terminating a pregnancy now had the definition of ensoulment to determine whether the formed being was a human. If abortion were to take place after the arrival of a soul, then the act would be considered a homicide and, therefore, sinful. Aquinas subscribed to this perspective, as evidenced by his view that “if one deliberately strikes a pregnant woman, knowing her to be pregnant and knowing of the risk of death, then 'if there results the death of either the woman or the animated foetus he will not be excused from homicide’” (Haldane and Lee, 2003, p. 262).


Figure 3: Botticelli's St. Thomas Aquinas.

Aquinas’and by extension, the medieval Catholic church’sconcept of delayed ensoulment seems to be directly in conflict with the modern position of the Church. Rather than accepting the idea that ensoulment occurs at forty and eighty days, the Church takes the position that an embryo is immediately ensouled upon fertilization (Brind'Amour, 2007). Therefore, any form of abortion is homicide due to its deliberate killing of a human soul. This serves to reveal an ever-changing perspective in the Church’s canon, as religious officials spent centuries grappling with the theological question of what exactly constitutes a human and at what point is a human infused with a soul.


It is evident that ancient and medieval philosophies regarding personhood and the moral action of abortion continue to influence modern rhetoric. Ranging from Aristotle’s potentiality principle to Aquinas’ belief in ensoulment, modern opinions on abortion are fundamentally grounded in these philosophers. Looking forward, it remains to be seen whether such philosophies will continue to serve as the baseline for the abortion question as some countries continue to liberalize legalization and others continue to restrict access.

Bibliographical References

Brind’Amour, K. (2007). St. Thomas Aquinas (c. 1225-1274). Embryo Project Encyclopedia. Retrieved from https://embryo.asu.edu/pages/st-thomas-aquinas-c-1225-1274


Dickison, S. K. (1973). Abortion in Antiquity. Arethusa, 6(1), 159–166. http://www.jstor.org/stable/26307468


Garrison, J. W. (2001). Rorty, Metaphysics, and the Education of Human Potential. In M. A. Peters & P. Ghiraldelli, Jr (Eds.), Richard Rorty: education, philosophy and politics, 46–66. Lanham, MD: Rowman & Littlefield.


Haldane, J., & Lee, P. (2003). Aquinas on Human Ensoulment, Abortion and the Value of Life. Philosophy, 78(304), 255–278. http://www.jstor.org/stable/3752047


Hare, R. M. (1975). Abortion and the Golden Rule. Philosophy and Public Affairs 4(3), 201-222.


Morgan, L. M. (2013). The Potentiality Principle from Aristotle to Abortion. Current Anthropology, 54(S7), S15–S25. https://doi.org/10.1086/670804

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