Stoic, Jewish, and Christian thought are . . . substantially agreed in this: that there is a set of rules or precepts of conduct, constituting a divine law, which is binding upon all rational creatures as such, and which in principle can be ascertained by human reason. This universal or common code is what Jews and Christians came to refer to as "morality" or "the moral law" (lex moralis). They also called it "the law of nature" (lex naturae) and "natural law" (lex naturalis), because they believed that the moral law applies to man by virtue of his nature as a rational being, and is known to him primarily by the exercise of natural human reason.
(Alan Donagan, The Theory of Morality [Chicago and London: The University of Chicago Press, 1977], 6 [ellipsis added])
