R.H. Helmholz begins his groundbreaking new book with a deceptively humble claim: In early modern Europe and early republican America, natural law had “real but limited success in determining the outcome of contested cases.”

Helmholz’s exhaustive analysis of historical records shows that arguments rooted in the natural law tradition influenced court cases in the years before the legal revolutions set in motion by the Napoleonic and American Civil Wars, but almost always in conjunction with citations of positive law. Natural Law in Court: A History of Legal Theory in Practice corrects those who dismiss natural law as mere ideological window dressing, as well as those who wish to present it as a comprehensive code properly determining cases and controversies of all kinds.

Today the natural law is, to say the least, not well understood. Helmholz takes a laudably practical approach to its definition. Eschewing theoretical disputes, he describes natural law as “the assumption that God had implanted certain principles of conduct and justice in the hearts of men and that these principles furnished a correct foundation for all positive law.” The law was assumed by nature to be rational, to recognize basic human dignity, and to uphold fundamental natural duties such as supporting one’s family. The intrinsic purpose of law, on this understanding, was for judges “to do right and secure to each person what was due to him.” Helmholz demonstrates this by sifting the evidence to assess what impact the natural law had in court.

The evidence, gleaned from case law and an extensive study of the texts and methods of legal education throughout the West, provided results that even surprised Helmholz, perhaps our most learned student of late medieval and early modern legal history. Natural law did not provide mere abstract statements of “some basic goals of the law.” Instead, it was looked to as a source of practical rules, as “a body of axioms for everyday judicial decision-making.”

Natural law axioms, rooted in a common assumption of law’s rational nature and intrinsic purposes, shaped a common legal language and mind. These were formed in different ways according to where and how lawyers trained. On the Continent, lawyers were required to receive a university education explicitly rooted in the natural law; they were taught from a variety of legal treatises explaining the nature and purposes of law as handed down in the Roman (“civil”) law tradition and in the canon law of the Church.

In England, most lawyers studied at the less formal and more practice-oriented Inns of Court; students nonetheless were exposed to treatises on using the natural law and to natural law argumentation in reports of common law cases. Yet more important in England was the presumption, often explicitly stated, that laws by nature accord with the dictates of reason and its natural offspring, natural justice.

As to the early United States, legal education throughout the early republican period can be summed up in the name William Blackstone. The natural law arguments of the Declaration of Independence and other arguments surrounding the War for Independence clearly had legal import. But Helmholz is too grounded in concrete aspects of law to overemphasize these materials, instead focusing on the pervasive influence of Blackstone’s great work from the 1760s: his Commentaries on the Laws of England, the primary source of most Americans’ legal education. The Commentaries went through multiple editions, including several brought out by prominent Americans that were extensively annotated to highlight their applicability to American cases. Including practical guidance and information, the Commentaries began with the law of nature (referenced more than 80 times) and its relation to the common law, which still applied in the former colonies.

What, then, was the impact of natural law in the Western world’s courts? Helmholz points to a number of famous cases in which the natural law clearly played a prominent role in the outcome, including Somerset’s Case (1772), in which the English court found that slavery’s denial of a person’s natural freedom was repugnant to natural law. Along with natural law, the decision relied upon the lack of a specific English statute protecting the slave-owner’s rights. The holding that resulted: a slave imported by his owner was in effect freed once he set foot on English soil. Helmholz is quick to point out that such decisions were not common and typically included references to positive law, but Somerset showed how arguments from nature could, at times, be important.

Statutory construction more generally was rooted in the presumption that the lawmaker could not have meant to violate natural justice, such that statutes should be read in a way that avoids such a result. Thus did natural law restrain the power of rulers. Natural law understandings over time became common law maxims with concrete implications—for example, the king is under the law and must keep his promises. Perhaps the most famous use of natural law reasoning in legal decision-making occurred in Bonham’s Case (1610). Here Sir Edward Coke held that a statute “against common right and reason” might be held null.

Issues of legal process, in effect limiting governmental power in the interests of individual rights, were of concern throughout the West. Legal process had explicit roots in the natural law—specifically in a right to self-defense derived by numerous judges and commentators from God’s having accused Adam of having eaten from the Tree of the Knowledge of Good and Evil before casting him out of Eden. It would be unnatural, it was argued, for a man, accorded by God Himself the right to hear the charges against him, to give up that right on entering civil society. These and other procedural concerns were raised in clear natural law terms, though, again, almost always buttressed by references to positive laws. They came to be formulated in the Anglo-American tradition as a right to due process. In America, they tended to be litigated in terms of constitutional rights, which lent them added power, but allowed all parties to forget or ignore their deeper grounding.

Such reasoning also was used regarding persons’ rights and duties in more mundane legal disputes. For example, the law of contract was shaped in significant measure by natural law assumptions that led courts to (for example) refuse to enforce a contract in which one party concealed material circumstances from the other. Where today presumptions against fraud would be explained away in terms of economic efficiency or would simply be taken for granted, English courts into the 19th century specifically noted their grounding in natural law duties.

The same can be said of a variety of legal maxims still active, though often caricatured, in American law. In Riggs v. Palmer (1889), for example, the court held that a convicted murderer could not inherit from the testator (his grandfather), whom he had murdered in order to secure his inheritance. The court stated that all laws

may be controlled in their operation and effect by general, fundamental maxims of the common law. No one shall be permitted to profit by his own fraud, or to take advantage of his own wrong.

Helmholz notes the continuity of this reasoning with Coke’s in Bonham’s Case. In effect, American courts “received” natural law through the Constitution and through common law maxims refined over centuries of development.

The contrast between the majority view in Riggs and the dissent, which argued that the letter of the law must be upheld regardless of the moral hazards thereby generated, was extremely pronounced. Indeed, it may be surpassed only by contemporary misinterpretations of the majority opinion. For today the Riggs decision is portrayed as a mere assertion by the majority of the primacy over law of vague social purposes—that is, as reasoning akin to the contemporary practice of judicial review.

Judges in the early republic on occasion did refuse to uphold governmental acts on natural law grounds, for example in a number of cases refusing to uphold state seizure of private property without compensation—cases handed down before the Fifth Amendment’s prohibition on such conduct was “found” to apply to the states. In many of these cases, natural law arguments played a significant role, though again almost always in conjunction with arguments rooted in statute and precedent.

As Helmholz is careful to point out, however, these cases do not resemble contemporary judicial review. Courts understood that “natural law did not authorize judges to strike down legislation because it conflicted with their own views of desirable public policy.” They simply read the law in accordance with maxims themselves rooted in natural law. These maxims had a long, storied history and played a powerful role in shaping constitutional law.

But public necessity and the common good often required enforcement of civil laws that veered from natural justice. Here Helmholz makes particular note of the prolonged development of laws concerning usury and their acceptance by courts. In family law, too (and especially in England),  primogeniture and other positive law doctrines essentially replaced significant aspects of natural law. As Thomas Aquinas himself acknowledged, prudence often demanded acceptance even of unjust, “corrupt” laws when necessary to maintain peace, order, and the public good. A law’s repugnance on natural law grounds provided an important reason for judges to limit its application and even hold it a “nullity” under the specific circumstances before it. It did not serve as license for judicial lawmaking.

What Helmholz has shown is that natural law mattered. It did not abolish slavery, enforce a “living wage,” or compel judges to reshape society into one of perfect justice. Indeed, it almost never served, on its own, as the basis for overturning an unjust law. But it did shape the mind and assumptions of judges and lawyers, enabling them to recognize the truism that law has normative purposes, that people do, in fact, expect that it will serve those purposes in a general sense, and that particular laws and their applications therefore should be read in light of those purposes.

The purposes themselves may be seen as rather abstract, such as providing due process, ruling under the law, and fulfilling one’s promises. But these purposes supported concrete rights and duties in both public and private law. They fostered a mutual confidence in contractual, constitutional, and familial duties—a confidence we have lost as judges have chosen to pursue justice through laws severed from their normative moorings.

It should not be surprising, then, that, having lost our faith in natural reason, we have not replaced natural law. It remains with us in the form of judicial maxims that too few judges and lawyers understand or use properly, but that remain essential to maintaining some kind of coherence in a profession increasingly dominated by cynicism, half-understood attempts at consistent legal positivism, and especially by the exercise of judicial will.