By St. Thomas Aquinas, The Catholic Thing, Nov. 5, 2019
As Augustine says, “There never seems to have been a law that was not just.” Thus it has the force of law insofar as it is just. In human affairs, something is said to be just insofar as it is right according to the rule of reason. The first rule of reason is, however, natural law. Thus every human law has the nature of a law insofar as it is derived from natural law. If it conflicts with natural law in any way, then it is not law but a corruption of law.
But it should be noted that something can be derived from the natural law in two ways: First, as conclusions from premises; second, as determinations of certain generalities. The first way is similar to that in which conclusions are demonstratively derived from premises in the sciences. The second is similar to the way general ideas are given special shape in the arts, as when a builder decides that he will actualize the general form of a house by constructing this or that particular model. ….
