THERE IS in fact a true law - namely right reason - which is in accordance with nature, applies to all men, and is unchangeable and eternal. By its commands this law summons men to the performance of their duties; by its prohibitions it restrains them from doing wrong. Its commands and prohibitions always influence good men, but are without effect upon the bad.
To invalidate this law by human legislation is never morally right nor is it permissible ever to restrict its operation, and to annul it wholly is impossible. Neither the Senate nor the people can absolve us from our obligation to obey this law, and it requires no Sextus Aelius to expound and interpret it. It will not lay down one rule at Rome and another at Athens, nor will it be one rule today and another tomorrow.
But there will be one law, eternal and unchangeable, binding at all times and upon all peoples; and there will be, as it were, one common master and ruler of men, namely God, who is the author of this law, its interpreter and its sponsor.
Republic III, 22.