Natural Law and Positive Law
In Germany, as with most countries on planet Earth, we drive on the right side of the road. We do this because of one line in a book called Straßenverkehrsordnung: “Fahrzeuge müssen die Fahrbahnen benutzen, von zwei Fahrbahnen die rechte." (STVO §2 (1), “Vehicles have to use traffic lanes, if there are two, the right one.") We would call that positive law. “Positive” because of the Latin word “positus”, the perfect passive participle of “pono” – to place, to put: The ministry of traffic has put it in place.
According to Thomas Aquinas, law “is nothing else than an ordinance of reason for the common good, made by him who has care of the community, and promulgated." (STh I-II q. 90) Does his definition hold for our traffic law?
The obligation to drive on the right side of the road is an ordinance of reason. The goal is to reduce the number of traffic accidents, so it is safe to say that it aims for the common good. The German ministry of traffic has made this rule, and they have the care of the community in this regard. They have published it in the Bundesgesetzblatt to promulgate it.
There are two main differences between this positive law and the natural law: the author and the way of promulgation. Positive law is human law. The author is always either a human being (e.g. a king) or an institution made up of human beings (e.g. a parliament). Being of human origin makes it subject to change. The author of natural law is God, and that makes it part of the eternal law. The way of promulgation for positive law today is mostly by publication in some book or periodical. Contrarily, we have a natural capacity to recognize natural law: our capacity of practical reason. (STh I-II q. 94)
These two forms of law are not disconnected entities standing side by side. In his Defense of Natural Law, Robert P. George shows that “the positive law is derived from the natural law in two different ways." (Oxford, 1999) It can be a direct deduction of natural law into positive law like the prohibition of the killing of innocents. It can also be more indirect, like the obligation to drive on the right side of the road. Natural law does not prescribe the use of the right lane for vehicular traffic. It is, however, necessary for the common good that we should regulate traffic. The details of the regulation lie in the creative freedom of the lawgiver. This also means that we cannot consider human laws breaking the prescriptions of natural law as laws.
Historically, we see first mentions of this concept in early Greek and Latin philosophy. “For Platon, justice has to concur with the nature of things and the soul." (Delhaye, Ph. “Geschichte des Naturrechts” in LThK2) Aristotle distinguishes between a right of nature and a right of law, as do the Stoics. Even though there is little evidence of natural law in scripture, Ambrose and Augustin have quickly adopted the pagan theory for the Church. While secular philosophers and political theorists have started to separate the spheres of morality and law since the Enlightenment, the Church has held on to the concept till the present day. The phrasing of Can. 1055 §1 CIC is an example of this: “The matrimonial covenant, […] which is ordered by its nature to the good of the spouses and the procreation and education of offspring, […]"
Since the 19th century, proponents of legal positivism reject this connection between a god-given (or otherwise pre-existing) natural law and the positive human law. (Häussling, J. M. “Rechtspositivismus” in LThK2) What remains is a theory of law with only formal conditions: Is the lawgiver he “who has care of the community,” and is the law promulgated?
In the 20th century, events have put the legal positivist idea to the test. Without a universal law to check them against, the actions of the concentration camp death squads and the border guards shooting down families who were trying to leave the GDR would be lawful. But as we can see in these extreme cases, common sense seems to demand that laws hold up against some higher standard. With the Nuremberg Trials (1946) and the International Declaration of Human Rights (1948), natural law made a short-lived comeback.