The origins of natural law theory in ethics can be traced back to the ancient Greek philosophers Plato (427-347) and Aristotle (384-322) who certainly employed various ideas central to it. But the first explicit formulation of the theory is found in the medieval Catholic philosopher St. Thomas Aquinas (1224-1274). Natural law theory is then subsequently developed over the centuries in various directions, many theistic (including God), some more secular in nature. Indeed, there are plenty of efforts currently underway to base natural law theory on evolutionary theory. But despite the nuances among these approaches, there are some basics that remain constant.
The Basics of the Theory
In ethics we are always trying to (1) consider theories that define ethical terms for us on a general and fundamental level; (2) consider various guiding principles based on these theories; and (3) see how these theories and principles can be used to make rationally justified moral judgments in the face of a variety of moral dilemmas. Natural law theory tries to satisfy (1)-(3) by looking to nature in order to define and distinguish good/bad and right/wrong. According to natural law theory, the unfolding of something in accordance with its nature is good, and right action will be action that facilitates this natural unfolding. So the recognition of the natural good comes first; then right action follows on this recognition.
The theory also maintains there are moral laws to be found in nature just like there are scientific laws to be found in nature. Recall that scientific laws are only descriptive: they are generalizations that claim to describe how the physical world does in fact work on a very fundamental and general level. For example, Isaac Newton’s Third Law of Motion (when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction to that of the first body) is just a description of how motion occurs on a general level. There is no prescription regarding what we should or should not do. But a natural moral law is prescriptive or normative insofar as it will tell us how we should act. If we can know natural moral laws then we can have moral guidance in our efforts to judge how to realize natural goodness. Indeed, these laws would be authoritative for all insofar as they, like so many scientific laws, would be universal, objective, and intelligible or capable of being understood. But how do we come to know these laws? Despite the differences between various natural law philosophers, the following two principles of knowing natural moral laws hold:
(1) We can know a natural law using our reason—we don’t need revelation from God or any mysterious capacities or talents.
(2) We can know what natural laws exist and how to apply them by rationally analyzing human nature, what our very essence is, and formulating moral prescriptions based on this essence.
Let’s consider a plausible example to make this less abstract. Aristotle argued that to fully understand something it is necessary to understand its natural purpose or essential function (telos in Greek). In Book I of his Nicomachean Ethics, Aristotle argues that mankind’s natural purpose is reason (see 1098a ff). It is the one trait unique to us and definitive of our nature. But if reason is our defining characteristic—our essence—then our natural purpose, according to Aristotle, is to actualize this potential reason as much as possible in the form of moral and intellectual virtue. By doing so we can become fully actualized human beings and reach happiness or fulfillment (eudemonia). Now once this view of human nature is in place we can formulate the following natural moral law:
NML: We should all develop our rational capacities.
Again, according to natural law theory, the unfolding of something in accordance with its nature is good and right action will be action that facilitates this natural unfolding. So the recognition of the good comes first; then right action follows on this recognition. In this case, we have the recognition of a natural good we possess—reason—and then we have a moral prescription of right action based on that recognition. Far from being just an unbiased description of what we in fact are—rational animals—it goes on to provide a prescription. This prescription can lead to concrete ways to guide our behavior and evaluate our motivations, the acts that follow from these motivations, and the consequences that follow from our acts. For example, we could argue that everyone should get educated and should have a right to education. After all, one of the bad consequences of not getting educated is that it prevents the realization of our rational nature. Moreover, any motive to prevent education would be bad and any act thwarting education would be wrong.
An Example from Martin Luther King, Jr.
Throughout history there are many examples of people appealing to a deeper, moral order in their efforts to criticize the unjust laws and practices of their time. Civil laws are made by particular people in particular societies. But if a certain society disintegrates then the civil laws of that society may or will disappear. Not so with natural laws: they exist independent of our wishes and decisions and provide a ground for morality that is universal, objective, and intelligible. As such, a natural law can be a powerful platform from which to morally and rationally criticize various unjust social practices. One of the best examples of this use of natural law can be seen in the following passages from Martin Luther King, Jr.’s “Letter from a Birmingham Jail” (April 16, 1963):
“Since we so diligently urge people to obey the Supreme Court’s decision of 1954 outlawing segregation in the public schools, at first glance it may seem rather paradoxical for us consciously to break laws. One may well ask: “How can you advocate breaking some laws and obeying others?” The answer lies in the fact that there are two types of laws: just and unjust. I would be the first to advocate obeying just laws. One has not only a legal but a moral responsibility to obey just laws. Conversely, one has a moral responsibility to disobey unjust laws. I would agree with St. Augustine that “an unjust law is no law at all.” Now, what is the difference between the two? How does one determine whether a law is just or unjust? A just law is a man made code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law. Any law that uplifts human personality is just. Any law that degrades human personality is unjust. All segregation statutes are unjust because segregation distorts the soul and damages the personality. It gives the segregator a false sense of superiority and the segregated a false sense of inferiority. Segregation, to use the terminology of the Jewish philosopher Martin Buber, substitutes an “I it” relationship for an “I thou” relationship and ends up relegating persons to the status of things. Hence segregation is not only politically, economically and sociologically unsound, it is morally wrong and sinful. Paul Tillich has said that sin is separation. Is not segregation an existential expression of man’s tragic separation, his awful estrangement, his terrible sinfulness? Thus it is that I can urge men to obey the 1954 decision of the Supreme Court, for it is morally right; and I can urge them to disobey segregation ordinances, for they are morally wrong…. We should never forget that everything Adolf Hitler did in Germany was “legal” and everything the Hungarian freedom fighters did in Hungary was “illegal.” It was “illegal” to aid and comfort a Jew in Hitler’s Germany. Even so, I am sure that, had I lived in Germany at the time, I would have aided and comforted my Jewish brothers. If today I lived in a Communist country where certain principles dear to the Christian faith are suppressed, I would openly advocate disobeying that country’s antireligious laws.”
Clearly we have an appeal to a moral law that is deeper than civil law and deeper than the racist social practices that are taken to be good by many people. And we can see the appeal to the good of natural development when he writes “any law that uplifts human personality is just. Any law that degrades human personality is unjust.” Insofar as certain laws facilitate good natural development they are just; if they thwart this natural development they are unjust. Notice, too, the reference to the great natural law theorist St. Thomas Aquinas, as well as the careful formulation as to the origins of the moral law: “A just law is a man made code that squares with the moral law or the law of God.” I think this formulation – “the moral law or the law of God – allows us to see how both a God-based and secular account of the moral law are compatible with his argument. There is room for many people of diverse persuasions to take something away from his words.
Of course natural law theory, like all moral theories, has many problems: do we really have a nature to discover and actualize? Perhaps we have no nature at all! And even if we do have a nature, can we really figure out what it is? And even if we could figure it out, can we really derive moral prescriptions from descriptions about human nature? And don’t we have plenty of disturbing natural traits? If so, how do we say which ones should be cultivated and which ones should not? Perhaps we are just bad creatures bound to be bad? Perhaps God did create us and therefore we are naturally good since we come from an all good source. But if God is needed to ground the theory then isn’t that bound to make this moral theory more complicated and problematic than other secular theories?
Those are just some of the common issues one has to face when trying to adopt natural law theory. Nevertheless, in reading Martin Luther King Jr.’s deeply moving passages one can see the theory’s great appeal: it can show that what is legal is not necessarily moral and that there is an objective, universal, and intelligible moral law that can serve as the foundation for moral and rational social critique.