Our subject is called natural law because it has the qualities of all law. Law has rightly been defined as an ordinance of reason, for the common good, made by the one who has care of the community, and promulgated. Considerthe natural law against murder. It is not an arbitrary whim, but a rule that the mind can grasp as right. It serves not some special interest, but the universal good. Its author has care of the universe, for he (God) created it. And it is not a secret rule, for God has so arranged his creation that every rational being knows about it.
Our subject is called natural law because it is built into the design of human nature and woven into the fabric of the normal human mind. Another reason for calling it natural is that we rightly take it to be about what really is—a rule like the prohibition of murder reflects not a mere illusion or projection, but genuine knowledge. It expresses the actual moral character of a certain kind of act.
“The Natural Law Is What We Naturally Know.” Intervju med J. Budziszewski (Religion & Liberty, Vol. 13, nr. 3 Mai-Juni 2003), s. 1. http://www.acton.org/publicat/randl/pdf/rl_v13n3.pdf (25.06.2007)