"THE human will can, by common agreement, make a thing to be just provided it be not, of itself, contrary to natural justice, and it is in such matters that positive right has its place. Hence the Philosopher says (Ethic. v, 7) that "in the case of the legal just, it does not matter in the first instance whether it takes one form or another, it only matters when once it is laid down." If, however, a thing is, of itself, contrary to natural right, the human will cannot make it just, for instance by decreeing that it is lawful to steal or to commit adultery. Hence it is written (Is 10:1): "Woe to them that make wicked laws.""
~St. Thomas Aquinas: Summa Theologica, II-II, Q. 57, Art. 2, ad. 2.
