102. Natural Law Theory and Social Justice, Part 1

The philosopher John Rawls, in the beginning of his classic book A Theory of Justice, wrote the following intuitively appealing description of justice:

“Justice is the first virtue of social institutions, as truth is of systems of thought. A theory however elegant and economical must be rejected or revised if it is untrue; likewise laws and institutions no matter how efficient and well-arranged must be reformed or abolished if they are unjust. Each person possesses an inviolability founded on justice that even the welfare of society as a whole cannot override. For this reason justice denies that the loss of freedom for some is made right by a greater good shared by others. It does not allow that the sacrifices imposed on a few are outweighed by the larger sum of the advantages enjoyed by many. Therefore in a just society the liberties of equal citizenship are taken as settled; the rights secured by justice are not subject to political bargaining or to the calculus of social interests.”

We can clarify this description by introducing three elements of justice articulated by John Finnis:

(1) Other-directedness: justice is ‘inter-subjective’ or interpersonal insofar as it is about relations and dealings with other persons.

(2) Duty: justice requires obligations to each other with regard to what is owed.

(3) Equality: justice is incompatible with any view that supports the good of any individual or group at the expense of another. Common forms of equality are equality before the law, material equality, political equality, and equal opportunity.

Given these elements, we can go on to discuss things like distributive justice, which seeks to fairly allocate the benefits and burdens of society thus limiting economic, racial, gender, and health inequalities, as well as commutative justice, which involves the regulation and treatment of individuals as far as certain social transactions and transgressions are concerned. We can also go on to formulate rights that protect people’s equality and establish a solid foundation for our obligations to one another.

Now let us ask: how can we rationally justify these ideas? To be sure, they sound nice and many people agree with them. Most people feel justice is good and can point to certain legal and political documents supporting it. But can we go deeper and provide a more fundamental foundation for these principles of social justice? We can if we turn to philosophy and utilize a moral theory that has traditionally been connected to social justice, namely, natural law theory. Indeed, this theory has served justice many times over the centuries and was employed by Martin Luther King, Jr. to argue that segregation is morally wrong. But what exactly is natural law theory? This is the first question I want to answer. Once we have a basic understanding of the theory, I want to show how King’s natural law theory argument against segregation can be generalized to show how all forms of social injustice are immoral. To anticipate, we will see that all acts of social injustice are immoral insofar as they hinder rather than help the development of our rational and free nature.

The Basics of Natural Law Theory

The origins of natural law theory can be traced back to ancient philosophers such as Heraclitus, Plato, Aristotle, Marcus Aurelius, and Cicero who employed ideas central to it. It was then developed by medieval thinkers such as Tertullian, Justinian, and St. Augustine. But perhaps the first comprehensive formulation of the theory appears in the writings of the medieval philosopher St. Thomas Aquinas. Natural law theory is then subsequently developed over the centuries in various directions, many theistic, some more secular in nature. Figures as diverse as Moses Maimonides, Francisco Suarez, Thomas Hobbes, Hugo Grotius, and John Locke made substantial philosophical contributions to its development. And the tradition continues to thrive in contemporary philosophy, political action, law, and religion. There are four basic ideas behind natural law theory that remain constant despite the diverse aspects of its rich tradition:

(1) There are moral laws to be found in nature just like there are scientific laws to be found in nature. Scientific laws are only descriptive: they are generalizations that claim to describe how the physical world does in fact work. 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. 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 scientific laws, would be universal (they would apply everywhere at all times), objective (not only a matter of personal or cultural opinion), and intelligible (capable of being rationally understood either immediately or after careful consideration).

(2) We can know a natural law using our reason—we don’t need revelation from God or any mysterious capacities or talents.

(3) We can know what natural laws exist by rationally analyzing human nature and formulating moral prescriptions based on this nature. It is important to point out that our essential traits are typically not things we infer from a fact or set of facts. Rather, we analyze human nature and then immediately see the traits as self-evidently good once all the relevant factors are understood.

(4) Once we have natural laws we can use them to justify natural rights. Natural rights will be those things that are essential to us if we are to realize our natural potential. Natural rights, just like natural laws, are not contingent on the decisions of a particular society like civil rights are. Rather, they are inalienable and necessary if our natural potentials are to be actualized at all.

Before turning to some historical examples of the theory in reference to social justice, let’s consider a plausible example to make things less abstract. Aristotle (322-384 BC) 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. Thus we could articulate a second natural moral law:

NML: Everyone should get educated and should have a right to education.

We could also argue that people shouldn’t grow up in a totalitarian regime where dissent is crushed and propaganda replaces the truth. After all, such a society would be bad insofar as truth and free debate are integral to the development of reason. And we could argue that forms of substance abuse that impair the proper function of the brain are wrong as well. These observations could also be formulated as natural laws offering us further guidance in many diverse areas of life.

Of course, there are many more natural traits than just reason. St. Thomas Aquinas’ (1224-1274) account is helpful in seeing what other traits we might consider. Aquinas was profoundly influenced by Aristotle and comprehensively developed his emphasis on the actualization of our natural rational potential within a Christian context. First, he argued that, as biological beings, we tend by nature to grow and mature and therefore we should preserve our being and our health by avoiding undue risks, eating healthy, exercising, etc. Second, we are animals capable of sensing the world around us. Therefore we ought to develop our senses and make use of them to observe, assess, understand, etc. Third, we are rational beings that can know the world and choose freely. Therefore, we should, on the one hand, develop our rational capacities through education and, on the other hand, develop our will and moral virtues like temperance and courage so we can choose wisely. Fourth, we are by nature social animals. Therefore, we should find ways to live harmoniously with one another under civil laws that do their best to reflect the prescriptions of natural laws. Lastly, we are created and sustained by an all good, all knowing, and all-powerful God. Therefore our greatest happiness can only come from being in the presence of God and therefore we should live a life in accordance with Christian teachings. Given this more comprehensive account, we can see how many prescriptions could be developed to guide us in various aspects of our lives.


Ethical theories attempt to: (1) define for us terms like good/bad and right/wrong on a general and fundamental level and (2) give us some guiding principle that will help us make and defend moral judgments. According to natural law theory, the unfolding of something in accordance with its essential nature is good; right action will be action that facilitates this natural unfolding; and action can be both guided and judged by articulating objective, intelligible, and universal natural moral laws found in human nature. These moral laws can then serve as guiding principles for moral inquiry. They can also serve as the grounds for natural rights that can help insure the flourishing of our essential nature.

In the next two parts of this series, we will look at a few examples of how natural law theory was used to combat social injustice.



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