Thus they share in the eternal reason and responsibly pursue their proper affairs and purposes. This communication of the eternal law to rational creatures is called the natural law. The natural light of reason, by which we discern what is right and wrong, is naught else but the impression on us of divine light. Natural right is contained in the eternal law primarily, and in the natural judicial faculty of human reason secondarily. The precepts of natural law are to practical reason what the first principles of science are to the theoretical reason.
Natural right is what is fitting and commensurate of man s very nature.
This may come about in two ways. Secondly by a judgement of the consequences. Taken in this sense, natural right is common to us and the other animals. But for the ordinary and rational human decencies more factors have to be allowed for. To appreciate a situation with an eye to how things will work out in practice is proper to human reason.