The law is promulgated words, by public authority, that is an ordinance of reason, for the common good.[1] Here, the current border policy of the United States aligns with the natural law. Thomas Aquinas teaches us there are four kinds of law: Eternal Law, Natural Law, Divine Law, and Human Law.[2] Law shapes human behavior by forming habits that, over time, alter a people’s customs, and it does so through four effects: commanding, prohibiting, permitting, and punishing.[3] Here, President Trump has prohibited the illegal aliens participating in the invasion of the southern border from being admissible in the United States.[4]

The Eternal Law is divine wisdom or providence, which directs all things to their due end, and was imprinted by God onto the human soul.[5] Man’s rational engagement with the Eternal law is called the natural law and is expressed through the seven precepts of the natural law.[6] Additionally, the eternal law is reflected in Divine law, revealed through the ordinances and commandments of both the Old and New Testaments.[7] Finally, the eternal law manifests in the “Law of Nature” as the law governing irrational beings, though such creatures cannot rationally comprehend or observe it.[8]

The Natural Law is man’s rational participation in God’s eternal law.[9] The first precept of the natural law is to first do good and avoid evil, and when applied to the six inclinations of man, the other six precepts reveal themselves.[10] Second, the preservation of self, using ordinary and reasonable means to preserve your life.[11] Third, the preservation of the species and to be fruitful and multiply reasonably, understanding that you are a gift of self to your spouse.[12] Fourth, to know truth and live by it.[13] Fifth, to live in society relationally, honoring friendship and solidarity.[14] Sixth, to refine the material riches of the universe as a gift of self in general. Seventh, to contemplate beauty and be thankful for it.[15]

These seven precepts lead us to the general principles of natural law. One may never do evil that good may come of it; whatever is intrinsically evil can never become good through motive or circumstance.[16] If an act is hostile to the flourishing of life, then it is intrinsically evil. Intrinsically evil acts can become more or less evil depending on the change in motive or circumstance but can never become good.[17] Intrinsically good acts can become more or less good depending on a change in motive or circumstance and can even become evil.[18] Circumstances will always turn indifferent acts into good or evil.[19] Those principles further lead us to conclusions about the natural law.[20]

There are two types of conclusions of natural law. Proper conclusions like divine authority and the Ten Commandments, and remote conclusions which are implicit in the conclusions of natural law, which are not generally known unless well-trained.[21] For example, thou shalt not steal is easy to see and understand, but returning lost goods takes more development.[22] Those natural law conclusions lead us to specifications or determinations of human law which rest on human authority alone.[23] While they do not always logically flow from the natural law principles, they must never contradict them.[24] One precept of the natural law cannot be advanced at the expense of another, and for a law (determination) to be good, it must vertically align with the conclusions, principles, and precepts that guide it.[25]

There are three sources of morality. The object chosen or the moral deed can be intrinsically good, evil, or neutral.[26] The end in view or intention and motive, the moral object is the end of the object, and the motive of the agent is the end of the subject.[27] The circumstances of the action condition the moral object because they determine the kind of concrete human act, or at least the degree or intensity of the act.[28] When applying the three sources of morality, if all three are not good, then the act is not a good act.[29]

The immigration act of August 3, 1882, allowed the Secretary of the Treasury to empower those who boarded ships to examine the immigrants therein.[30] If they found a passenger was a “convict, lunatic, idiot, or any person unable to take care of himself or herself without becoming a public charge,” then the ship was not permitted to land.[31] The modern categories for inadmissible aliens include health-related grounds, criminal and related grounds, security-related grounds, those who would become a public charge, illegal entrants and immigration violators, draft evaders, aliens previously removed, practicing polygamists, and child traffickers.[32] Most of the modern categories that determine who is inadmissible and who is not have their own exceptions more closely tied to reason than they were in 1892.

President Donald J. Trump issued Presidential Proclamation No. 10888 on January 20th, 2025, declaring the situation at the southern border as an invasion under Article IV, Section 4 of the Constitution while acting at his “maximum” authority under Article II powers.[33] Under Aquinas’s framework, the morality of stopping mass illegal immigration must be evaluated through the three sources of morality: the object chosen, the intention, and the circumstances.[34]

The object chosen, arresting and deporting an unlawful alien, is likely intrinsically good, or at the very least neutral. To remove a person from a place they do not belong, as defined by rational law, is intrinsically good.

The intention and motive are likely intrinsically good because preservation of self, family, and country by rational means is a good act and violates no natural law precept or principle. It advances living relationally and the preservation of self because an ordered society enables people and families to flourish in peace, security, and friendly obligation, all of which further the common good.

The circumstances of 2024 determined the degree and intensity of good in the President’s proclamation. The president described the circumstances that made this order necessary: a massive number of illegal crossings overwhelmed immigration systems, threatened national security, strained public resources, and endangered public health.[35] St. Thomas Aquinas examined how the Old Testament addressed foreigners, putting them into three categories: passers-through, resident aliens, and those from hostile nations. Aquinas’s analysis, therefore, focuses on two groups relevant to mass illegal immigration: those seeking residency and those from hostile nations.[36] Residency seekers had to wait for their citizenship until the common good was firmly at heart. This was because “if foreigners were allowed to meddle with the affairs of a nation as soon as they settled down in its midst, many dangers might occur, since the foreigners not yet having the common good firmly at heart might attempt something hurtful to the people.”[37] The government could exclude people from hostile nations in perpetuity, and those eventually allowed entry had to wait for generations and make a positive demonstration of an act of virtue.[38] Therefore, the severity of the circumstances in 2024 intensified the moral weight of exclusionary measures, rendering the President’s proclamation consistent with Aquinas’s understanding of a good and moral act.

In sum, the current border policy of the United States aligns with the natural law, as articulated by St. Thomas Aquinas. President Trump’s proclamation to suspend the entry of unlawful aliens was an inherently good act. The executive and legislative action surrounding the border crisis in 2024 was an objectively good and reasonable act that was right with reason.

[1] St. Thomas Aquinas, Summa Theologiae, I‑II, Q. 95, Art. 4

[2] Id. at I‑II, Q. 91

[3] Id. at I‑II, Q. 95–Q. 97

[4] Presidential Proclamation No. 10888, Guaranteeing the States Protection Against Invasion, 90 Fed. Reg. 8333 (Jan. 20, 2025).

[5] D. Brian Scarnecchia, Bioethics, Law, and Human Life Issues: A Catholic Perspective on Marriage, Family, Contraception, Abortion, Reproductive Technology, and Death and Dying 36-38 (2010).

[6] Id.

[7] J. Budziszewski, Commentary on Thomas Aquinas’s Treatise on Law (Cambridge Univ. Press 2014) xviii; D. Brian Scarnecchia, Bioethics, Law, and Human Life Issues: A Catholic Perspective on Marriage, Family, Contraception, Abortion, Reproductive Technology, and Death and Dying 40 (2010).

[8] J. Budziszewski, Commentary on Thomas Aquinas’s Treatise on Law (Cambridge Univ. Press 2014) xviii

[9] D. Brian Scarnecchia, supra note 5.

[10] Id. at 38-39.

[11] Id. at 39.

[12] Id.

[13] Id.

[14] Id.

[15] Id.

[16] Id. at 57.

[17] Id. at 58.

[18] Id. at 59.

[19] Id.

[20] St. Thomas Aquinas, Summa Theologiae, I‑II, Q. 95, Art. 2

[21] Id. at I‑II, Q. 95, Art. 4

[22] Id. at  I‑II, Q. 95, Art. 2

[23] Id. at I‑II, Q. 95, Art. 2

[24] Id. at I‑II, Q. 91, Art. 3

[25] St. Thomas Aquinas, Summa Theologiae, I‑II, Q. 94, Art. 2

[26] D. Brian Scarnecchia, supra note 5, at 52.

[27] Id. at 53-55.

[28] Id. at 55-56.

[29] Id. at 56.

[30] Nishimura Ekiu v. U.S., 142 U.S. 651, 660 (1892).

[31] Id. at 661.

[32] 8 U.S.C. 1182

[33] Presidential Proclamation No. 10888, Guaranteeing the States Protection Against Invasion, 90 Fed. Reg. 8333 (Jan. 20, 2025); Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579, 635 (1952) (Jackson Concurrence)

[34] D. Brian Scarnecchia, supra note 5, at 51.

[35] Presidential Proclamation No. 10888, Guaranteeing the States Protection Against Invasion, 90 Fed. Reg. 8333 (Jan. 20, 2025).

[36] John M. Grondelski, Pondering the Wisdom of St. Thomas Aquinas on Immigration, Catholic World Report (Oct. 8, 2025), https://www.catholicworldreport.com/2025/10/08/pondering-the-wisdom-of-st-thomas-aquinas-on-immigration/

[37] St. Thomas Aquinas, Summa Theologiae, II‑II, Q. 103, Art. 3

[38] John M. Grondelski, supra note 36.