The Natural Law Origins of Private and Public Law

Daniel Z. Epstein, St. Thomas University College of Law


This article attempts to counter the widespread skepticism that surrounds any appeal to natural law principles, starting with Roman law at one end and the appeal to general law under Swift v. Tyson on the other. It steers a systematic middle course between moral absolutism, which treats all relationships as fixed and immutable, and modern realist positions that insist the infinite variety of legal approaches to most legal problems proves that there is no solid core to either natural law or general law. The natural law positions set out the basic relationships for marriage and family, for alluvion and avulsion of rivers and streams, for the formation of agreements, and for the transfer of various forms of property under the private law. But at that point, these rules may be modified as needed to create strong Pareto improvements by the introduction of various formalities that improve the security of transactions or, more substantively, which overcome key holdout issues that can arise, for example in the upper airspace on the one side or with caves on the other.

These principles can carry over to public law as well. Systems of taxation have to be structured (with flat taxes) as the best way to avoid theft from one group to another, and also for eminent domain powers when the public must be compensated, unless under the police power they are designed to prevent wrongful conduct from the party regulated, as under the common law of nuisance, which is not subject to infinite variation. Similarly on procedural matters, the two Roman principles of “hear the other side” (audi alterem partem) in cases before a neutral judge and “no one shall be a judge in his own cause” (nemo judex in causa sua) have to apply universally whereas other fact finding devices, for example juries, are subject to wider variations. These principles were tested in the Insular Cases where this norm held in check any American impulse to dictate legal practices and norms to conquered groups. This rule that explains why the Supreme Court was correct in refusing to hear the case intended to compel American Samoa to force federal citizenship on indigenous peoples who refused to have it. These basic natural law principles, most notably the rule that no one should profit from his own wrong explains, contrary to today’s understandings, why the common principle of birthright citizenship applies only to the offspring of legal aliens, but not illegal ones.

In dealing with the transition between Swift and Erie Railroad v. Tompkins, the key insight is that Swift was correct insofar as it used a set of general (i.e., neutral) principles to decide disputes that took place across state lines, but not for those that took place solely within a given state. Thus, using general principles for negotiable instruments and boundary disputes eliminates local favoritism and gravitates to the best of common practices. But there is no reason to use these common principles for complex private disputes (rules for mortgages or local antitrust laws) where the general law (as expanded before Erie) often slights local interests, such that the key decision in Clearfield Trust v. United States reestablishing general common law for negotiable interests and Hinderlider v. La Plata River & Cherry Creek Ditch Co. with respect to boundary disputes, pushed the law back in its correct direction.

It is only by patiently working through all of these ancient and modern, private and public law cases, the conceptual unity of our basic legal system can be defended.