Father Pegues continues his exposition of St. Thomas Aquinas’ teaching on law by discussing a second type of law: the natural law.
The natural law is “that inborn light of man’s practical reason by which he is able to direct himself and to act with knowledge consciously in such wise that his acts execute the eternal law, just as the natural actions of things produced by virtue of their natural inclination execute this same law unconsciously.”
The first precept of the natural law in man is that “man must seek what is good and avoid what is evil.” All the other precepts of the natural law are “applications thereof more or less immediate.” The first applications concern (1) “whatever is beneficial for or perfects his physical life”; (2) “whatever helps towards the conservation of the human species”; and (3) “whatever conduces to the welfare of his life as a rational being.”
“There follows from this that whatever is essential for the conservation of this threefold life, or that can help towards its perfection, is proclaimed a good thing by the practical reason of every man, in such a way, however, that among the three goods there is a certain subordination, so that by way of dignity the good of the reason comes first, then the good of the species, and then the good of the individual.” As regards the good of the individual, “this principle proclaims that man must eat for the sustenance of his body, and that he may never attempt his life.” As regards the good of the species, “this principle proclaims that there must be human beings who concern themselves with the conservation of the species by taking upon themselves the burden as well as the joys of fatherhood and motherhood; and that it is never lawful to do anything which tends to frustrate the object of fatherhood and motherhood.” As regards the good of reason, “this principle proclaims that man, who is the work of God from whom he has received his all, and who was made to live in the society of other men, should honour God as his Sovereign Lord and Master, and should act towards his fellow-beings according as the nature of his relations with them demands.”
Quotations from Thomas Pegues, Catechism of the “Summa Theologica” of Saint Thomas Aquinas, trans. Aelred Whitacre (New York: Benziger, 1922).