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Abortion Ethics: Natural Law vs. Naturalism

This article will examine (1) natural law’s and (2) naturalism’s opposing views on abortion. Their diverse philosophies determine radically divergent abortion ethics, which will be examined solely through natural reasoning.

Pertinent Thomistic Doctrines

Since embryology teaches that specifically human life begins at conception, modern natural law ethics – following the principles of St. Thomas Aquinas (1225-1274) – prohibits direct abortion at any stage, since it is the taking of innocent human life. This position is consistent with the philosophical doctrine of hylemorphism, which teaches that all physical substances are composed of matter and form. Since form determines what kind of thing a substance is, the human substantial form, or soul, determines the presence of human life. Soul determines that something is a single, unified living organism of a given species.

Embryology makes clear that a specifically human organism, distinct from the body of its mother, begins life at the moment of fertilization. “Zygote” is simply a technical name for the first single-celled human organism. That selfsame human organism lives throughout all the later stages of fetal development, birth, infancy, pubescence, adulthood, and senescence – until death.

Because the same individual human substance lives from conception to death, no change makes it suddenly become a person based on acquisition of certain properties, say, cognitive abilities. If it is a person at any later stage of life, it is a person at conception and has the same personal rights throughout life.

Rationality belongs to the human essence throughout life, even though sentient and rational faculties become active as organic functions develop. We do not become human at a certain point of development, only to later lose our human rights because of irreversible dementia. The distinction between potency and act is crucial. The human organism is always a person with rights in act, even though various human faculties may go from potency to act and even back to potency later.

Specifically human faculties (operative potencies) are not yet in act with respect to their operations – but are fully in act with respect to existence, even from the time of conception.

These faculties, which are immaterial properties of the human soul, must not be confused with mere brain organization, which, when sufficiently developed, is used for the faculties’ operations. While a certain brain organization is needed for understanding to occur, it is the intellectual faculty that actually allows the person to think. Mere physical brain activity cannot even perceive sensible images as a whole, and certainly cannot form universal concepts.

This is why faculties must be present from conception, since they have no way of later developing in the immaterial substantial form – and brain function alone can neither think nor sense. The faculties of the soul are needed, so they must begin existence when the soul does.

There has to be a distinction between the substance itself and its operative potencies (powers, faculties). Otherwise, the act of the substance (existence) would be identical to the acts of the faculties (sensing, thinking) – meaning that when not sensing or thinking a man would stop existing!

The faculties exist continuously, while they go into act and sometimes cease acting, and then, begin acting again.

For example, I can be not thinking or seeing, and then begin thinking or seeing, and then cease thinking or seeing again – all the while continuing to (1) exist as a substance and (2) possess the powers to think and to see.

Since this continuously living human organism belongs to the species of rational animal, it is what Boethius defined as a “person,” since “a person is a supposit (substance) of a rational nature. The only other such created persons are angels.

Natural Law and Abortion

Natural law ethics defines murder as the gravely immoral evil of directly taking innocent human life. Decent men recognize this as a basic moral precept. Without space to defend this precept fully, the argument begins that rights flow from obligations. God gives us life and obliges us to live it well so as to attain the Supreme Good, God himself. That obligation gives us the corresponding right to live. Because others must respect our right to live, it is immoral to violate that right by taking an innocent human life.

Abortion is such an immoral act -- evil by its very nature (intrinsically evil), since it directly attacks the most fundamental human right. Nor can such an act be justified by any utilitarian purpose, however good, since natural law forbids using an intrinsically evil means to attain a good end.

Up to half of embryos die before implantation. Could their genetic material be so defective that they do not constitute human life? Could one infer that very early stage abortion might be licit? But, those which do survive are human lives and ought not be killed. Those that do not survive either were human or not. If not, then, since they die anyway, there is no reason to kill them. But, if they were human lives, then killing them is clearly immoral. So, the objection is pointless.

But, did not St. Thomas accept the outdated successive animation theory that the human soul is not present at conception, but rather appears in the third month, after a vegetative and then sentient soul was present in the first and second months of gestation? Yes, he provisionally accepted Aristotle’s reasoning about this, because the ancients did not see how the early stages’ matter looked fit for the human form.

Modern Thomists know that the material organization of the human organism, even as a single-celled zygote, is uniquely specific to the human species, as evinced by the uniquely human DNA present in every living human cell, even in its initial stages. Hence, they now correctly insist that the human form must be present, even in the zygote.

Naturalism's Abortion Stance

Accepting neither God nor a spiritual and immortal human soul, naturalism approaches abortion’s ethics very differently. Ethical norms themselves are based, not on some transcendental metaphysics, but simply common human approbation of what is right or wrong, possibly augmented by some claim of evolutionary advantage to those who practice such norms. Absent natural law foundations, many different theories are advanced.

For example, the principle not to take innocent human life is not viewed as protective of all human organisms. Rather, criteria as to who merits the “right-to-life-conferring” designation of a “person” are considered and applied only as “warranted.”

This means that the human zygote is not considered a person because it lacks certain “personhood” properties, including sentience, self-consciousness, rationality, creativity, socialization, and so forth. Depending upon criteria selected, different stages of fetal development may or may not be granted full human status, with birth being an important event for both ethical and legal purposes.

The gaining of personhood and its corresponding right to life, then, is seen as a gradual process. Properties, such as various levels of cognitive awareness, birth giving “embodiment in the world,” and even societal acceptance, become benchmarks by which personhood is more or less arbitrarily conferred upon the developing human organisms.

Using this reasoning, various seeming paradoxes can be explained. For example, a baby born several weeks prematurely is presently considered a legal person with a right to life, whereas a full term fetus can be aborted at the moment prior to natural birth, since he is still not born – even though neurologically more fully developed than the prematurely born baby.

One explanation is that birth itself confers “embodiment into the world,” and thus establishes a claim for the premature infant that is lacking to the as yet unborn full term fetus.

For naturalists, the defining characteristic of the human person becomes the development of some brain function that enables activities which fulfill “person conferring” criteria, such as certain cognitive abilities.

Hylemorphism vs. Atomism

Central is the question of whether the human zygote is correctly described as (1) a hylemorphic unity, that is, living things are made substantially one being by having an immaterial form that unifies the matter and places it into the human species, or (2) as simply a product of biological evolution, that is, a group of synergistically interacting organic molecules with no metaphysical uniting principle.

Because naturalism ascribes no substantial form having special human powers to the human zygote, there is no basis for saying that the zygote is a “rational animal” that would fulfill Boethius’s definition of the person, or, for that matter, any other definition of person that naturalists would accept.

Naturalism rejects God’s existence, typically by espousing atomism -- the claim that all reality ultimately reduces to the smallest physical units: atoms or subatomic particles. Thus, the focus is now on atomism.

Does hylemorphism or atomism correctly describe the zygote? Several arguments show that hylemorphism prevails.

First, without hylemorphism, not only is the substantial unity of the zygote denied, but so is that of all later stages of human development. Substantial unity means that a thing is undivided in itself and distinct from other beings.

This is crucial because we do not even exist without such unity. My video, “Atheistic Materialism,” shows that Richard Dawkins does not exist – based on his own atomistic premises.

If one takes atomism seriously, the only things that really exist are whatever basic atomic or subatomic units of matter one selects as ultimate. For sake of argument, let us consider that the building blocks of organic chemistry and of organisms are atoms. And atoms combine to make larger entities, be they molecules or entire organisms.

The logic is as simple as this: When two atoms combine chemically, say, sodium and chlorine, do they become one thing (salt?), or are they really still two things (two distinct atoms), functionally associated? Atomism logically is forced to the latter position, since all that really exists is atoms, even though they may enter into temporary chemical bonds with other atoms.

The same logic must be followed all the way up through the zygote, the newborn, and the adult human being -- including Dr. Dawkins. Atomism is ontologically committed to the sole realities being atoms, despite highly-complex chemical bonding taking place in functional unities (organisms) obeying DNA dictates.

This means that zygotes are not persons, not merely because they lack certain cognitive abilities, but because they lack substantial unity.

In a word, the philosophy of atomism or naturalism may exist, but atomists and naturalists do not.

Absent some real unifying principle, such as form, atomism’s self-defeating truth is that nothing really exists above the atomic level. This is why there is no stable principle of existence on which naturalism can depend to establish a principle of “personhood.” Atomism’s most embarrassing “public secret” is that, not only is the zygote not a person (on its false premises), but there is no unified supposit, substance, thing… on which to ground the notion of personhood at all.

Even the concept of “neural networks or patterns” suffers the same problem. A certain neural pattern may exhibit cognitive activity, much like a computer with AI, but there is no “there” there to be the person having “personhood.” Just atoms exchanging outer orbit electrons. That’s all.

Atomists have abolished substantial forms. But they have also abolished themselves in the process!

The entire debate over when personhood is present, based on various cognitive or other criteria, misses the point – since the same atomism that denies full human rights to the zygote also denies the ontological basis for the substantial existence of any person at any stage of human life.

The only way to avoid this intellectual suicide is to grant that there is some principle of existential unity above the atomic level in living organisms, including the zygote. Dare we call it a “substantial form?”

What atomism lacks is a stable principle of unification for living organisms. That is why naturalists struggle to designate the point at which the “person” finally appears in fetal development.

“Personhood” never can appear in naturalism, since all that really exists is the atoms – not the atomists who believe this fantasy.

At best, the concept of personhood that atomism can support is that of a certain neural pattern that has “achieved” epiphenomenal consciousness. This functionally, but not substantially, unified neural pattern would then become the “person,” using the entire organism, brain and all, like a parasite alien invading a victim host.

Even then, the neural pattern’s consciousness could not be just material atoms, since even sense experience of the wholeness of images must be immaterial, as shown in an earlier Strange Notions piece.

Conversely, if zygotes really exist as substantial unities, hylemorphism reappears – together with continuously existing substances and powers, whose secondary cognitive activities come and go.

Naturalism lacks a continuous principle of substantial unity for the living organism. What hylemorphism has is an essential nature that is present from conception to death – a nature manifesting fully human cognitive abilities sometime after conception.

Previously, I have shown non-material activities of sentient and intellectual substances comport with hylemorphism, but not atomism’s materialism -- specifically by pointing to (1) sentient cognitive abilities shared by lower animals to apprehend sense data as a whole (which no material device can do), and (2) spiritual intellectual abilities found in man by which he forms universal concepts. Atomism can explain none of these abilities.

Ethical and Legal Principles

Two principles pertain to abortion:

  1. It is never licit to directly kill an innocent human being.
  2. It is never licit to perform an action unless one is morally certain that it will not directly kill an innocent human being.

These principles have substantial acceptance, both in ethics and in law.

Regarding the first principle, it is the primary obligation of society or the state to protect the innocent human life of every human person within its jurisdiction. With respect to secondary rights, such as bodily autonomy and consent, these rights are limited insofar as they violate the more primary right to life of another human being. Autonomy and consent over my body ends when it allows me to destroy your body and life. That the right to life is more primary than any other right follows from the fact that unless one is alive, no other rights can exist.

The second principle reflects a common sense provision of law. People go to jail for shooting humans they fail to make certain were deer.

For hylemorphism, human life begins at conception and is a continuous substantial entity until death. All scientific evidence supports that the same organism present at conception is the one present in adulthood. Therefore, the same substantial form must be present from conception to death. As shown above, this includes the soul’s immaterial faculties. Since the form of the adult is clearly human and a person, the soul and human person must have been present from conception on.

Therefore abortion is always morally wrong and to be condemned. And since it is wrong by its very nature (intrinsically wrong), no set of circumstances or good intentions or outcomes can possibly justify it – for no good end can ever justify an intrinsically evil means to that end.

But what of the view of atomism?

Since neural networks capable of “human” acts, such as creativity, do not develop until a certain point in gestation, or even at birth in the case of “embodiment in the world,” atomists claim specifically human faculties are non-existent until such neural development. Thus, they can claim moral certitude (beyond a reasonable doubt) that a “person” does not yet exist, and thus, abortion violates no human rights.

But, as demonstrated above, in atomism the human organism has no substantial unity at any stage of its existence. All that exists are individual atoms. There is never a substantially unified single being to serve as a substrate for “personhood.”

At best, the “person” turns out to be a certain neural complex of atoms, developed in the human brain, having no substantial unity. Even then, no purely physical neural complex can grasp the wholeness of an extended image in a single, simple act. To do this, an immaterial form is needed, which atomism rejects.

With no immaterial “form” to unite the neural network, its existential experiences of unity and selfhood have no rational basis. Conversely, the existential experience of the self bespeaks some kind of substantial unity, which atomism cannot explain.


Never even having heard of hylemorphism, the common sense metaphysical insights of most people will lead them rightly to suspect that, if we are a single organism as adults, we must have been one as a human zygote – and that the same individual human life developed from conception into the adult we encounter as a person today.

For that reason, most citizens who follow the ethical principles enunciated above will conclude that one cannot, with moral certainty, say at which point the human organism became a person. Being uncertain of this point, they may well conclude that it would be as immoral to kill the unborn child at any point. For this reason, we should not be surprised if legislators conclude that the common ethical principles of society operate to protect the unborn.

While some will protest that society has no right to violate the autonomy and consent of women with pro-life legislation, since most people recognize that the first obligation of society is to protect the life of its innocent members, pro-life legislation may find increasing support.

Dr. Dennis Bonnette

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Dr. Dennis Bonnette retired as a Full Professor of Philosophy in 2003 from Niagara University in Lewiston, New York. He taught philosophy there for thirty-six years and served as Chairman of the Philosophy Department from 1992 to 2002. He lives in Youngstown, New York, with his wife, Lois. They have seven adult children and twenty-five grandchildren. He received his doctorate in philosophy from the University of Notre Dame in 1970. Dr. Bonnette taught philosophy at the college level for 40 years, and is now teaching free courses at the Aquinas School of Philosophy in Lewiston, New York. He is the author of two books, Aquinas' Proofs for God's Existence (The Hague: Martinus-Nijhoff, 1972) and Origin of the Human Species (Ave Maria, FL: Sapientia Press, third edition, 2014), and many scholarly articles.

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