Natural Law Arguments

All creation declares abortion’s ingratitude and rebellion against our Creator. But men make science their god and mock God’s truths, so we are tempted to retreat within the walls of special revelation, consigning the natural world and its scientific investigation as a pagan domain. This is a grave mistake. Natural revelation is a key part of knowing and understanding God. God’s book of nature helps us to know what He has done and how He works among us. Indeed, Scripture itself teaches us to ask, “Does not even nature itself teach you?” (1 Cor. 11:14).

Those truths proclaimed by nature must not be abandoned in favor of those truths revealed by Scripture.105 Nature is a handmaid to Scripture. It too reveals the character of God, at times in areas Scripture does not. Sacred Scripture is infallible, yet not all texts of Scripture are spoken with equal clarity; where Scripture is unclear, the book of nature helps us evaluate what interpretations of God’s Word are most sound.106 Some of our fallible understandings of Scripture need refinement by nature.107 Properly understood, natural revelation cannot contradict special revelation.108 Any conflict between natural and special revelation, then, is due to some error in our interpretation of either (or both).

Conversely, when both of God’s spheres of revelation address a matter, we do well to take special heed. Thus we here state that our condemnation of abortion is not only based on God’s written moral law, but also God’s book of nature. Together they bear unanimous testimony against the monstrosity of this crime.

Man as Unique Creation

Scientific research shows that, from the moment of conception, the unborn child possesses all the genetic information that distinguishes him from any other created species or being. The unborn child conceived in his mother is not a tree, monkey, or tumor.109 He is a human being bearing the image of God with forty-six chromosomes and the DNA that sets him apart from the rest of creation. He is demonstrably different from either his father or mother, with DNA drawn from both of them. He is a unique human being.

As detailed earlier, physicians have tried to change the definition of conception from fertilization to successful implantation in the mother’s womb. But this change makes a mockery of science and reason. The safe attachment of the child to his mother’s womb does not change him in any way. There is no scientific or rational reason why implantation should define the beginning of life or qualify that life for protection. It is true that, from implantation, the little one’s reliance on his mother for nourishment increases, but this increase does not bear on his right of protection. Indeed, such an argument contradicts one typical argument for abortion “rights”—namely, that one person dependent on another is less deserving of protections and rights. What a callous response to the interrelatedness of life, and specifically the charity God commands between us in light of His charity toward us!

Personhood from the Beginning

If, for the sake of argument, we grant that the personhood of the human embryo is not yet proven to exist at fertilization, arguments based on this irrational supposition still fall flat. For, in order to justify the moral rectitude of abortion at any point, one would need to establish that there is no possibility of the abortion killing a person. Yet it is impossible to demonstrate the newly conceived embryo lacks personhood. Indeed, all the evidence is to the contrary.

Again, if for the sake of argument we were to accept this irrational premise, it would immediately leave us asking at what stage of later embryonic development personhood is acquired? At what stage does what is not man somehow become man?

The irrationality of this project is clear to everyone who has not allowed himself to become a bloody ideologue. This little one is a living human being when he emerges from his mother’s womb because he is a living being at the moment when his life qua human begins—always and forevermore at conception.

Yes, we can muddy the waters by raising abstract, speculative questions on ensoulment, personhood, or quickening, desperately working to deny that conception is the beginning of life. But why such intensity in our efforts to deny protection to these little ones? The truth is, throughout history, men (often with better intentions than our own) have discussed the mystery of how and when our heavenly Father “ensouls” an infant. Many of the church fathers wrote extensively on the matter, yet their opinions were never settled matters of dogma, in large part because Scripture does not directly address the topic.110 Nor did these theories cause the slightest hesitation in their condemning abortion as a grave sin from the moment of conception. In Evangelium Vitae, John Paul II puts it directly:

Some people try to justify abortion by claiming that the result of conception, at least up to a certain number of days, cannot yet be considered a personal human life. But in fact, “from the time that the ovum is fertilized, a life is begun which is neither that of the father nor 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. . . .”

Furthermore, what is at stake is so important that, from the standpoint of moral obligation, the mere probability that a human person is involved would suffice to justify an absolutely clear prohibition of any intervention aimed at killing a human embryo. Precisely for this reason, over and above all scientific debates . . . , the Church has always taught and continues to teach that the result of human procreation, from the first moment of its existence, must be guaranteed that unconditional respect which is morally due to the human being in his or her totality and unity as body and spirit.111

The church has always taught and continues to teach that abortion is the direct assault upon the providence and authority of God, our Creator.

SLED Arguments

Many of the arguments employed by advocates of abortion can be divided into four categories referred to by the acronym SLED, referring to the Size, Level of development, Environment, and Degree of dependency of the preborn child.112

  1. Size: Some argue abortion is justified because these little ones are beyond our view. It is permissible to kill the little one because he is too small to see hidden inside his mother’s womb.

    Yet God’s creation is full of small organisms and many of them have the protection of law and the sympathy of society, such as the world’s smallest primate and smallest marine mammal. Shall we justify the killing of these organisms because of their size? On the contrary, it is much more grievous to destroy these little ones because of how tiny and defenseless they are. Only a monster would argue that the smaller and weaker the baby, the less claim that baby has on our protection.

  2. Level of development: Some argue the limitations of the child during his early development make it permissible to kill him. The unborn child can’t feel pain, can’t think, isn’t self-aware, and is not yet sentient, so we may kill him.

    Yet science is proving the little one’s sensitivity to his environment at younger and younger stages of his life in the womb.113 The limitations of development are irrelevant. One’s right to life is not dependent on one’s capacities to enjoy life or assert his personhood. Children or adults who suffer sickness, wounds, or genetic anomalies which leave them with limited capacities have as much claim to society’s protection as those with no such limitations, both outside and inside the womb.

  3. Environment: Some argue the environment in which the unborn child exists invalidates his right to be considered human. Since the unborn child doesn’t, for example, breathe air, he is sufficiently “other” so that he deserves no protection.

    Of course, the same argument would never be made concerning residents of the South Pole or the International Space Station. Neither of those locations can sustain life naturally without the provision of extraordinarily complicated and costly artificial supports. The same can be said concerning victims of polio who have, for decades, continued to live only by the support of an iron lung.114

  4. Degree of dependence: Some argue the unborn child’s dependence upon his mother undermines his right to the protection of his life.

    This argument is especially pernicious, for it strikes at the heart of one of the principal blessings God has ordained in human society, which is our interdependence. God has woven interdependence across His creation: the tree and soil, the citizen and ruler, the husband and wife, teacher and student, doctor and patient; and most preciously, mother and child.

    No man is an island.115 No man is independent. By arguing that dependence diminishes value, this argument also targets the handicapped, the elderly, the sick, the infirm, and anyone who depends on another for nourishment and care. This is the trajectory of the pro-abortion argument. This world of callous disregard for the weak and defenseless must be rejected.

  1. “When they are able, from reliable evidence, to prove some fact of physical science, we shall show that it is not contrary to our Scripture. But when they produce from any of their books a theory contrary to Scripture, and therefore contrary to the catholic faith, either we shall have some ability to demonstrate that it is absolutely false, or at least we ourselves will hold it so without any shadow of a doubt. And so we will cling to our Mediator, ‘in whom are hidden all the treasures of wisdom and knowledge,’ that we will not be led astray by the glib talk of false philosophy or frightened by the superstition of false religion.” Augustine, Literal Commentary on Genesis 1.21.41, trans. J. H. Taylor.↩︎

  2. Thus Augustine, on the question of the physical disposition of heaven: “But someone may ask: ‘Is not Scripture opposed to those who hold that heaven is spherical, when it says “who stretches out heaven like a skin”?’ Let it be opposed indeed if their statement is false. The truth is rather in what God reveals than in what groping men surmise. But if they are able to establish their doctrine with proofs that cannot be denied, we must show that this statement of Scripture about the skin is not opposed to the truth of their conclusions. . . . But if it is necessary, as it surely is, to interpret these two passages so that they are shown not to be contradictory but to be reconcilable, it is also necessary that both of these passages should not contradict the stories that may be supported by true evidence, by which heaven is said to be curved on all sides in the shape of a sphere, provide only that this is proved.” Literal Commentary on Genesis 2.9.↩︎

  3. “It is admitted that theologians are not infallible, in the interpretation of Scripture. It may, therefore, happen in the future, as it has in the past, that interpretations of the Bible, long confidently received, must be modified or abandoned, to bring revelation into harmony with what God teaches in his works. This change of view as to the true meaning of the Bible may be a painful trial to the Church, but it does not in the least impair the authority of the Scriptures. They remain infallible; we are merely convicted of having mistaken their meaning.” Charles Hodge, Systematic Theology, 3 vols. (1872–73; Eerdmans, 1982), 1:59.↩︎

  4. Indeed, because God is infallible in all His works and cannot err in His revelation of Himself, both natural and special revelation may be said to be infallible, but not any interpretation of those revelations.↩︎

  5. “Well, after all, it’s living, isn’t it? And if it’s living, what is it if it’s not a human being? A mouse? A dog? A monkey?” Richard John Neuhaus in an unpublished paper given at the Consultation on the Church and Abortion, sponsored by Presbyterians Pro-Life, Princeton Theological Seminary, February 28–29, 1992.↩︎

  6. See Job 10:8–12: “Your hands fashioned and made me altogether, and would You destroy me? Remember now, that You have made me as clay; and would You turn me into dust again? Did You not pour me out like milk and curdle me like cheese; clothe me with skin and flesh, and knit me together with bones and sinews? You have granted me life and lovingkindness; and Your care has preserved my spirit.”↩︎

  7. John Paul II, Evangelium Vitae, March 25, 1995, §§ 60–61,, quoting Sacred Congregation for the Doctrine of the Faith, Declaration on Procured Abortion, November 18, 1974, §§ 12–13,↩︎

  8. The SLED acronym was developed by the Roman Catholic philosopher Stephen Schwarz in his 1990 book The Moral Question of Abortion (Loyola University Press).↩︎

  9. Re: sight, eye movements and reactions occur as early as 12 weeks. See Tryphena Humphrey, “Some Correlations between the Appearance of Human Fetal Reflexes and the Development of the Nervous System,” in Progress in Brain Research, vol. 4, Growth and Maturation of the Brain, ed. Dominick P. Purpura and J. P. Schadé (Elsevier, 1964), 93–135,

    Re: hearing, see Christine Moon, Hugo Lagerkrantz, and Patricia Kuhl, “Language Experienced In Utero Affects Vowel Perception after Birth: A Two-Country Study,” Acta Paediatrica 102, no. 2 (February 2013): 156–160,; also Eino Partanen et al., “Learning-Induced Neural Plasticity of Speech Processing before Birth,” in Psychological and Cognitive Sciences 110, no. 37 (August 26, 2013): 15145–15150,

    Re: pain, recent research has continually pushed back the developmental threshold at which the unborn are known to be able to feel pain. See, e.g., Stuart Derbyshire and John Bockmann, “Reconsidering Fetal Pain,” Journal of Medical Ethics 46, no. 1 (2020): 3–6, For other aspects of early fetal development, see Katrina Furth, 15 Facts at 15 Weeks, On Science 3 (Arlington: Charlotte Lozier Institute, 2021),↩︎

  10. Linda Rodriguez McRobbie, “The Man in the Iron Lung,” The Guardian, May 26, 2020,↩︎

  11. John Donne, Devotions upon Emergent Occasions (1624), ch. 17.↩︎