The Natural Law (NL) is a well-developed scientific theory of law and is the basis of all legal systems in Western Thought. It was a system of law and political thinking which placed the law at the service of the human person. It presupposed that the human mind was capable of knowing truth, particularly the truth about the human person and the goal of human life.
The value system in the NL was based upon a rational concept of human nature and the perfection of that nature. The goal for the law, both civil and moral, was to protect the common pursuit of authentic human happiness. This good was not individualist and subjective. It was based in the human ability to know truth, universal and objective. NL presupposes the freedom of the human person to choose means appropriate for the attainment of the authentic good of human life, the good which is actually capable of winning the desire of all human beings. The subjective experience of that good is what is known as happiness. NL was not created by the Catholic Church but was the system of law and morality that, of necessity, was acknowledged and presupposed when Christians began their dialogue with the world.
Natural law wisdom was considered to be scientific wisdom and was accepted by the US political and legal systems until the early twentieth century. The most cited law books in the decisions of the US Supreme Court in the first half of the history of this country were the volumes of Blackstone's Commentaries on the Laws of England. Blackstone's views on Natural Law were essentially those accepted for millenia and acknowledged by Catholic thinkers. Natural Law was eventually replaced in the US legal system due to the strident efforts of certain legal thinkers who created a new system of thought. Most legal students today have no knowledge of the principles of the radical reinvention of the legal system that took place about a century ago.
NL began to be questioned by legal philosophers under the influence of the Pragamatists and political Progressivist Movement at the end of the 19th Century. Those who sought to revise the legal system believed in a theory of Social Darwinism and thought that law should be used as a means to bring about the new social eutopia. The "end" in this case were goals that the legislators and judges selected apart from any theory of human nature or other systems of valuing based upon a rational understanding of nature. The novelty of these ideas in the history of law can be seen in the inchoate state of the revised theory of law.
The new legal theory did not contain a system of valuing. The influence of the theory led to the creation of system of law that is no longer concerned with human flourishing which leads to happiness. Instead, by default, the orientation of legal theory became something akin to HLA Hart's view of freedom, the maximum expression of social freedom against every limitation. However, that has not solved the problem resulting from the lack of a theory of value. It is recognized that there must be limitations upon freedom of choice, but without a rational basis for valuing behavior, it is not clear today what the basis should be for establishing such limitations. This hiatus continues to lead to critical conflicts in political and legal processes. As the influence of the new theory continues to advance, there is an increasing tendency to equate any limitation on free choice as an impediment to happiness. But this concept is purely subjectivist. One will note that the concept of the "pursuit of happiness" as a value for law, and as stated in the Declaration of Independence, is unintelligible and seems unattainable in a diverse and pluralistic culture.
The early scholars of the transformation of the US political and legal system in the 20th were Roscoe Pound, Dean of Harvard Law School, and US Supreme Court Justice Oliver Wendell Holmes, Jr. Their main objective was to use the law to achieve social ends. Pound, in particular, sought to transform the judiciary into a means for a "more effective social engineering" (Pound's own words). Those familiar with Holmes will be aware of the fact that Holmes was a eugenicist, as were many of his contemporaries. Holmes and Pound were familiar with, and apparently accepted, the instrumentalist logic of John Dewey and the similar legal views of the German legal scholar, Gerhard von Ihering who wrote, Law as a Means to an End. Holmes's eugencist views apparently became part of his way of using the law to achieve desired social ends. Holmes wrote the US Supreme Court decision upholding the forced sterilization of Carrie Buck in Virginia saying "three generations of imbeciles is enough." By the middle of the 20th Century, the revisionists' theory of law, which was pragmatic and instrumentalist, became predominant at bench and bar and in the law schools of the country. This information has been well documented in research by Roberts Summers of Cornell University School of Law and other legal historians.