Today’s Catechism sections discuss the Natural Moral Law. Supporting material comes from St. Augustine’s “On the Trinity”.

I. The Natural Moral Law

1954 Man participates in the wisdom and goodness of the Creator who gives him mastery over his acts and the ability to govern himself with a view to the true and the good.

The natural law expresses the original moral sense which enables man to discern by reason the good and the evil, the truth and the lie:

The natural law is written and engraved in the soul of each and every man, because it is human reason ordaining him to do good and forbidding him to sin . . . But this command of human reason would not have the force of law if it were not the voice and interpreter of a higher reason to which our spirit and our freedom must be submitted.5

1955 The "divine and natural" law6 shows man the way to follow so as to practice the good and attain his end. The natural law states the first and essential precepts which govern the moral life. It hinges upon the desire for God and submission to him, who is the source and judge of all that is good, as well as upon the sense that the other is one's equal. Its principal precepts are expressed in the Decalogue. This law is called "natural," not in reference to the nature of irrational beings, but because reason which decrees it properly belongs to human nature:

Where then are these rules written, if not in the book of that light we call the truth? In it is written every just law; from it the law passes into the heart of the man who does justice, not that it migrates into it, but that it places its imprint on it, like a seal on a ring that passes onto wax, without leaving the ring.7

The natural law is nothing other than the light of understanding placed in us by God; through it we know what we must do and what we must avoid. God has given this light or law at the creation.8

1956 The natural law, present in the heart of each man and established by reason, is universal in its precepts and its authority extends to all men. It expresses the dignity of the person and determines the basis for his fundamental rights and duties:

For there is a true law: right reason. It is in conformity with nature, is diffused among all men, and is immutable and eternal; its orders summon to duty; its prohibitions turn away from offense .... To replace it with a contrary law is a sacrilege; failure to apply even one of its provisions is forbidden; no one can abrogate it entirely.9

1957 Application of the natural law varies greatly; it can demand reflection that takes account of various conditions of life according to places, times, and circumstances. Nevertheless, in the diversity of cultures, the natural law remains as a rule that binds men among themselves and imposes on them, beyond the inevitable differences, common principles.

1958 The natural law is immutable and permanent throughout the variations of history;10 it subsists under the flux of ideas and customs and supports their progress. The rules that express it remain substantially valid. Even when it is rejected in its very principles, it cannot be destroyed or removed from the heart of man. It always rises again in the life of individuals and societies:

Theft is surely punished by your law, O Lord, and by the law that is written in the human heart, the law that iniquity itself does not efface.11

1959 The natural law, the Creator's very good work, provides the solid foundation on which man can build the structure of moral rules to guide his choices. It also provides the indispensable moral foundation for building the human community. Finally, it provides the necessary basis for the civil law with which it is connected, whether by a reflection that draws conclusions from its principles, or by additions of a positive and juridical nature.

1960 The precepts of natural law are not perceived by everyone clearly and immediately. In the present situation sinful man needs grace and revelation so moral and religious truths may be known "by everyone with facility, with firm certainty and with no admixture of error."12 The natural law provides revealed law and grace with a foundation prepared by God and in accordance with the work of the Spirit.


1978 The natural law is a participation in God's wisdom and goodness by man formed in the image of his Creator. It expresses the dignity of the human person and forms the basis of his fundamental rights and duties.

1979 The natural law is immutable, permanent throughout history. The rules that express it remain substantially valid. It is a necessary foundation for the erection of moral rules and civil law.

In his work, “On the Trinity” (14, 15, 21), St. Augustine discusses the natural law.

21. And of this certainly it feels no doubt, that it is wretched, and longs to be blessed nor can it hope for the possibility of this on any other ground than its own changeableness for if it were not changeable, then, as it could not become wretched after being blessed, so neither could it become blessed after being wretched. And what could have made it wretched under an omnipotent and good God, except its own sin and the righteousness of its Lord? And what will make it blessed, unless its own merit, and its Lord's reward? But its merit, too, is His grace, whose reward will be its blessedness; for it cannot give itself the righteousness it has lost, and so has not. For this it received when man was created, and assuredly lost it by sinning. Therefore it receives righteousness, that on account of this it may deserve to receive blessedness; and hence the apostle truly says to it, when beginning to be proud as it were of its own good, For what have you that you did not receive? Now if you received it, why do you glory as if you had not received it? But when it rightly remembers its own Lord, having received His Spirit, then, because it is so taught by an inward teaching, it feels wholly that it cannot rise save by His affection freely given, nor has been able to fall save by its own defection freely chosen. Certainly it does not remember its own blessedness; since that has been, but is not, and it has utterly forgotten it, and therefore cannot even be reminded of it. But it believes what the trustworthy Scriptures of its God tell of that blessedness, which were written by His prophet, and tell of the blessedness of Paradise, and hand down to us historical information of that first both good and ill of man. And it remembers the Lord its God; for He always is, nor has been and is not, nor is but has not been; but as He never will not be, so He never was not. And He is whole everywhere. And hence it both lives, and is moved, and is in Him; and so it can remember Him. Not because it recollects the having known Him in Adam or anywhere else before the life of this present body, or when it was first made in order to be implanted in this body; for it remembers nothing at all of all this. Whatever there is of this, it has been blotted out by forgetfulness. But it is reminded, that it may be turned to God, as though to that light by which it was in some way touched, even when turned away from Him. For hence it is that even the ungodly think of eternity, and rightly blame and rightly praise many things in the morals of men. And by what rules do they thus judge, except by those wherein they see how men ought to live, even though they themselves do not so live? And where do they see these rules? For they do not see them in their own [moral] nature; since no doubt these things are to be seen by the mind, and their minds are confessedly changeable, but these rules are seen as unchangeable by him who can see them at all; nor yet in the character of their own mind, since these rules are rules of righteousness, and their minds are confessedly unrighteous. Where indeed are these rules written, wherein even the unrighteous recognizes what is righteous, wherein he discerns that he ought to have what he himself has not? Where, then, are they written, unless in the book of that Light which is called Truth? Whence every righteous law is copied and transferred (not by migrating to it, but by being as it were impressed upon it) to the heart of the man that works righteousness; as the impression from a ring passes into the wax, yet does not leave the ring. But he who works not, and yet sees how he ought to work, he is the man that is turned away from that light, which yet touches him. But he who does not even see how he ought to live, sins indeed with more excuse, because he is not a transgressor of a law that he knows; but even he too is just touched sometimes by the splendor of the everywhere present truth, when upon admonition he confesses.


5 Leo XIII, Libertas praestantissimum, 597.
6 GS 89 # 1.
7 St. Augustine, De Trin. 14, 15, 21: PL 42,1052.
8 St. Thomas Aquinas, Dec. praec. I.
9 Cicero, Rep. III, 22, 33.
10 Cf. GS 10.
11 St. Augustine, Conf. 2, 4, 9: PL 32, 678.
12 Pius XII, Humani generis: DS 3876; cf. Dei Filius 2: DS 3005.