A RATIONAL FOUNDATION OF ETHICS
"MANKIND is ruled by two laws: Natural Law and Custom. Natural Law is that which is contained in the Scriptures and the Gospel." These words are taken from another great law-book, the authority of which for a time evenly balanced that of the Corpus Iuris Civilis. They form the opening paragraph of the Decretum Gratiani (ca. 1140), the oldest collectio of Church law embodied in the Corpus Iuris Canonici.1 They provide the best introduction to the medieval conception of the law of nature.
Once again that ancient notion was called to play a capital role in the history of thought. In the hands of professional philosophers it became the corner-stone of a complete system of ethics. But that remarkable achievement would probably not have been possible had not the notion of natural law undergone a thorough transformation. The lawyers of the Church-- the Canonists--stand out among medieval lawyers for the freedom and daring with which they recast the whole problem of law and morals. They gave natural law an unprecedented coherence, clearness and force. Canon law has been said, and correctly, to constitute the principal vehicle, in the Middle Ages, of the doctrine of the law of nature2____________________