Law is something to be discovered

"In the Roman law system—a somewhat decentralized legal system superior in many ways to the common law—Roman jurists (jurisconsults) helped develop the great body of Roman law by providing opinions on the best way to resolve disputes. These disputes were often purely hypothetical or imaginary cases, in which the jurists asked: “under such and such a possible or conceivable combination of circumstances, what would the law require?”25 It is conceivable that a large part or even all of the legal code existing in a given society can be “deduced” in this fashion, and then these rules applied like precedents to actual controversies as they arise.

As a libertarian (and, I confess, a lawyer), I must say that I believe I would be more comfortable living under a set of concrete rules deduced by libertarian philosophers than the(perhaps more concrete) set of rules developed under the actual common law.

[The civil law was derived from principles developed in a common-law fashion in the Roman law. It is the Roman law, more than the more positivistic and legislation-worshiping civil law, that bears a similarity with the common law. See Kinsella (1995, pp. 135–36).]

Still, Barnett’s argument in favor of a common-law system makes sense, even to libertarians who favor a deductive approach to rights (Hoppe 1989b, p. 131; Rothbard 1998; Kinsella 1997, pp. 607–45). Legal rules must be concrete in the sense that the rules must take into account the entire relevant factual context. Since there are an infinite number of factual situations that could exist in interactions between individuals, a process which focuses on actual cases or controversies is likely to produce the most “interesting” or useful rules.26

It probably makes little sense devoting scarce time and resources to developing legal precepts for imaginary or unrealistic scenarios. If nothing else, a common-law type system that develops and refines legal precepts as new cases arise serves as a sort of filter that selects which disputes (i.e., real, commonly-encountered ones) to devote attention to. Barnett thus makes a convincing case that, in a decentralized legal system such as the English common law (or the early Roman law, the Law Merchant, and even modern arbitral systems)—especially one in which judges or arbitrators attempt to apply fundamental notions of justice to concrete situations—it is reasonable to expect a body of concrete legal concepts and precepts to develop, which are more or less compatible with fundamental notions of justice.27

If and when unjust legal precepts do arise, they are not necessarily permanent because a common-law process allows them to be modified or replaced when this becomes apparent. However, unless it is clear that a given legal precept is inconsistent with justice, then there should be reluctance to jettison established legal rules or precedents. This thus gives rise to the legal doctrine of stare decisis (or jurisprudence constante in continental or civil-law systems) (Kinsella 1994, p. 1278)."

Review Essays: KNOWLEDGE, CALCULATION, CONFLICT, AND LAW - N. STEPHAN KINSELLA
THE STRUCTURE OF LIBERTY: JUSTICE AND THE RULE OF LAW. BY RANDY E. BARNETT. NEW
YORK: OXFORD UNIVERSITY (CLARENDON) PRESS, 1998.