III.

Christian Conceptions

Christians found the natural law doctrine of the Stoics quite compatible with their beliefs. St. Paul spoke of Gentiles who do not have the Mosaic law doing “by nature what the law requires” (Romans 2:14). The 6th-century Spanish theologian St. Isidore of Seville affirmed that natural law is observed everywhere by natural instinct; he cited as illustrations the laws ordaining marriage and the procreation of children. Texts from Isidore cited at the beginning of the Italian scholar Gratian's Decretum (circa 1140), the canon law textbook of the Middle Ages, stimulated extensive discussion among the Scholastics. The teaching of St. Thomas Aquinas on the natural law is the most widely known. In his Summa Theologiae (Summary Treatise of Theology, 1265-73) Aquinas called the rational guidance of creation by God the “Eternal Law.” The Eternal Law gives all beings the inclination to those actions and aims that are proper to them. Rational creatures, by directing their own actions and guiding the actions of others, share in divine reason itself. “This participation in the Eternal Law by rational creatures is called the Natural Law.” Its dictates correspond to the basic inclinations of human nature. Thus, according to Aquinas, it is possible to distinguish good from evil by the natural light of reason.