Only ‘Just Laws’ That Follow Natural Law Serve as the Foundation for Realizing True Good and Happiness
St. Thomas Aquinas viewed law as a protective barrier that enables humans to realize their rational nature and achieve happiness within the community.
However, he never agreed with the claim that “an unjust law is still a law,” a notion widely misinterpreted and disseminated based on Socrates’ words. Rather, he argued that an unjust law is “not a law but a corruption of the law” (I-II, 95, 2) or “violence” (96, 4). If a law does not aim for the common good but operates for the benefit of a specific group or the desires of those in power, it has lost its true nature. In such cases, it goes beyond a crisis of the rule of law to become a serious threat to human dignity. Therefore, the legitimacy of a law is not determined solely by form or procedure but by whether its content aligns with justice and the good.
In fact, throughout history, there have been many instances where rules took the form of law but destroyed human dignity. Laws that institutionalized racial discrimination, laws that deprived specific religious or ethnic groups of their rights, and emergency measures enacted to silence political opponents may all appear to be laws on the surface. However, by Thomas’s standards, they are not an order of reason aimed at the common good, but rather closer to the institutionalization of a distorted will of power. The racial laws of Nazi Germany and the apartheid legislation of South Africa are prime examples illustrating this point.
Particularly amid the crisis of positivism facing modern society, laws lacking a moral foundation do nothing but cause social chaos, let alone guide human conscience. To resolve the tension between the protective function of law and its potential for corruption, it is essential to clearly establish the criteria for a “just law.” This raises a fundamental question: What, exactly, makes a law just? Thomas’s answer is presented in terms of the relationship between natural law and eternal law.
Every just human legal system must be understood as part of the grand order of eternal law; human law possesses the authority of true law only when it reflects the objective truth indicated by eternal law.
The First Principle of Natural Law: “Do Good and Avoid Evil”
Thomas argues that just as the law of non-contradiction is the first principle of reason in the realm of speculative science, so too is there a first principle of ethics in the realm of morality: “Do good and pursue it, and avoid evil” (I-II, 94, 2). Thomas seeks the objective good presented in this seemingly simple principle within the concept of “natural law (lex naturalis).”
