Nature isn’t complicated.  An animal behaves according to its nature.  Nothing more is needed to explain it.  Human action is no different.  There’s an objective structure to ethics rooted in the facts of human existence.  Natural law is discoverable by reason, not invented by preference.  Its principles are often ignored, not because they are unclear, but because they limit the ambitions of those who seek control.  As Rothbard noted, even defenders of liberty routinely fail to understand the natural law they claim to support.

At the center is an absolute principle of justice: the ability to determine what counts as violence in human relationships.  John Locke understood this clearly.  “Every man has a property in his own person.” When an individual mixes his labor with unowned resources, the result becomes his property.  This is not an opinion.  It is a logical extension of self-ownership.

The distinction between ethics and morals follows from this.  Ethics concerns what one may do with one’s own property without invading another’s.  Morals refer to what a community approves or disapproves.  Morals vary, ethics don’t.  Ethics identifies whether an action is legally permissible in the natural law.  Morals identify whether others find the action admirable.  Confusing these two has allowed the state to smuggle preference into legality.

Natural law requires no value system.  It’s value-free.  It simply describes the boundary where violence begins.  Policy isn’t value-free.  Even minor regulation is an expression of someone’s preferences imposed on someone else’s property.  When natural law is understood, these values become obvious.  They reveal who’s introducing coercion through the backdoor and who benefits from the intrusion.

Consider the classic example.  Crusoe fishes.  Friday gathers berries.  Crusoe’s fish are Crusoe’s because he produced them.  Friday’s berries are Friday’s for the same reason.  If Friday demands Crusoe surrender fish against his will, that demand isn’t natural law.  It is positive law—law created by Friday and enforced against Crusoe.  Natural law is discovered.  Positive law is created.

The conflict between the two is simple.  Natural law defines boundaries that no human can alter.  Positive law is an attempt to redraw those boundaries for someone’s advantage.  Wherever positive law contradicts natural law, violence is legitimized by decree.

That’s the entire structure: natural law discovered by reason, positive law imposed by men.

Reference

Murray Rothbard; The Ethics of Liberty