Catholics, Non-Catholics, and the Natural Law

Given the general decline in public morals, and given the fact that, as an institution, the major promoter of the natural law is the Catholic Church, some are led to conclude that the natural law is a “Catholic thing,” or that it only binds Catholics. The natural law is Catholic inasmuch as it is an integral part of the Catholic moral system, but it is not a subject of the supernatural revelation that Christ bequeathed to His Church. It is something given to all men as strictly binding.

Even Catholics are confused about this and think that, as long as a non-Catholic follows his conscience, he is not bound to the natural law. But this goes against scripture (as well as the notion of what a conscience is): St. Paul said “when the Gentiles, who have not the law, do by nature those things that are of the law; these having not the law are a law to themselves” (Romans 2:14). This is generally interpreted to mean that those who did not have the benefit of the revelation of the Old Testament (specifically the Mosaic Law) were still naturally endowed by their Creator with consciences capable of judging good and evil. The next verse goes on to say that these pagans show “the work of the law written in their hearts, their conscience bearing witness to them, and their thoughts between themselves accusing, or also defending one another.”

That the moral law binds all men is a truth of the Catholic Faith universally believed. While many churchmen are confused and confusing on the issue, the Church still officially teaches this (indeed she cannot cease doing so). Vatican II, in its Gaudium et Spes, speaks of this law written on the heart: “In the depths of his conscience, man detects a law which he does not impose upon himself, but which holds him to obedience. Always summoning him to love good and avoid evil, the voice of conscience when necessary speaks to his heart: do this, shun that. For man has in his heart a law written by God; to obey it is the very dignity of man; according to it he will be judged.”[1]

This conciliar passage footnotes passages from St. Thomas’ Summa Theologica (II-II, q. 32, a. 5 ad 2; and q. 66, a. 2) where the Angelic Doctor affirms that all human beings, not only Catholics, know the eternal law of God to the extent that they know the universal principles of the natural law. So the council fathers clearly had in mind the universality of the natural law. The teaching is not unique to St. Thomas: “The general teaching of theologians is that the supreme and primary principles [of the natural law] are necessarily known to every one having the actual use of reason.”[2] This is why everyone knows, for instance, that murder is wrong.
To the non-Catholic who may claim that natural law does not bind him because it is “Catholic,” I would propose the following:

  1. “Do good and avoid evil” – the first precept of the natural law – is found in the legal codes, philosophical works, religious books, and literary monuments of all civilizations, ancient and modern.
  2. Many of the secondary precepts of the natural law – e.g., prohibitions of murder, theft, and adultery – are found in those same historical records, such as the Code of Hammurabi, the ancient Babylonian legal code.[3]
  3. Much of modern literature, which seeks to be “value free,” is filled with stories of the bitterness of guilt which visits those who violate their consciences in matters of the primary and secondary precepts of the natural law.

In short, the common experience of mankind acknowledges the universality of the natural law.

But there is more. Obedience to the natural law is necessary, but it is not enough to make man truly right or just. Supernatural revelation is needed to make man right, both to heal him of Original Sin and to elevate him to attain his final goal, which is a supernatural end. The natural law, which is naturally knowable, can help to bring someone into the Catholic Church. Especially nowadays, as fewer institutions stand up for the natural law, those with a good will, who earnestly seek to keep that law, can see that the law written on their heart corresponds to the moral law defended by the Catholic Church.

According to Dr. John Haas, “The approach of the natural law helps us enter into dialog with other peoples who may not share our particular religious beliefs. The natural law and the doctrine of the Catholic Church tell us that the Church’s basic moral teachings, whether they have to do with euthanasia, contraception, or the ways in which one wages war apply to everybody.”[4]

This truth can help us to evangelize. How? First, it is foundational, as we have said, that the natural law applies to all men and that all have a knowledge of its fundamental precepts. Second, the Church’s moral teachings conform perfectly to this law. Therefore, since all men know these principles in some degree, they will see the basic moral teachings of the Church as good and reasonable; therefore, the natural law provides a moral terminus a quo from which to begin in our conversations with non-Catholics.

Building upon that, we acknowledge, with St. Thomas and most other theologians, that there will be confusion about the application of the secondary principles of the natural law. Now, as St. Thomas teaches in the Summa Contra Gentiles, those who desire knowledge also desire to flee ignorance[5] and that which is imperfect desires to be perfected.[6] Therefore, people in pursuit of greater clarity, knowledge, and understanding of the law that is written in their hearts – if their pursuit be accompanied by a resolute good will – will see the reasonableness of those moral teachings of the Catholic faith, teachings which clarify the secondary precepts of the natural law.

This, of course, could be a grace leading to their conversion.


[1]Gaudium et Spes, No. 16. Translation on Vatican web site:
documents/vat-ii_cons_19651207_gaudium-et-spes_en.html (emphasis mine).

[2]The Catholic Encyclopedia, Volume IX, (Robert Appleton Company: 1910)

[3]Class notes, “Lecture 2: Natural Law.”


[5]III, 50, 6.

[6]III, 50, 2.