The concept that there is a system of justice inherent in the world that is more certain, more just, and superior to the written laws of any society, which are always specific to time and place and made by imperfect human beings, and therefore fallible. The idea that there is an objectively discoverable set of principles of right moral conduct was originally postulated by the early philosophers in the classical period and has run through Western thought ever since.
In ancient Greece, Plato (c. 429-347 B.C.E.) conceived of law as a disposition or arrangement of reason, which was one of his “Universals” or “Forms.” Later, Aristotle (384-322 B.C.E.) thought that the permanent and change¬ less universal law was more important than laws written by states, which were the product of individuals like himself and therefore liable to errors of judgment. The Roman Stoic conception of universal reason led Cicero (106-43 B.C.E.) to believe that there are natural laws that have been built into the universe by a rational deity. The medieval Christian philosopher/theologian St. Thomas Aquinas (c. 1225-1274 C.E.) synthesized Catholic theology and Aristotelian metaphysics. He defined natural law in relation to God’s eternal law and held that the eternal law is Gods reason, which governs the relationship of all things in the universe to each other. Thomists (Aquinas’s followers) said that this eternal law is conveyed to human beings in part through revelation and in part by their own reason, introspection and dialogue, and it is the latter, the part that can discerned by reason and which relates to their own behavior, that is natural law. According to this thinking, the principles of natural law must not be understood to be immutable but could be allowed to be variously developed at different times and in different places. Protestant theologians like Karl Barth (1886-1968) and many others criticized this notion, holding that sinful and sinful and fallen men and women cannot have any direct knowledge of God’s intent without the special aid of revelation.