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What Is Natural Law?

Understanding the Nature of Law: A Foundational Perspective


The concept of law is foundational to both human society and the moral framework within which individuals operate. Law, in its essence, serves as a measure or rule by which human actions are directed or restrained. It is not merely a set of arbitrary rules but a principle of action rooted in reason and aimed at guiding individuals toward the common good. As Thomas Aquinas famously articulated, law is a rule or measure of human activity, where reason directs actions toward their proper ends (Aquinas, Summa Theologica, 1a2ae. 90, 1). This understanding of law as a guiding principle is essential to grasp before delving into the specific kinds of law, particularly natural law, and their implications.


Law, as a first principle of action, is concerned with directing human behavior toward an ultimate end, which is often identified as the common good or happiness. This concept is not merely a human invention but is rooted in the very nature of being and reason. Just as there are first principles of thought, such as the law of non-contradiction, there are also first principles of action, such as the directive to "do good and shun evil." These first principles form the foundation of natural law, which is the focus of our exploration.



The Proclamation and Effectiveness of Law


For any law to be effective, it must be communicated or proclaimed to those it governs. The principle that no one is obligated to obey a law of which they are unaware is both reasonable and just. Aquinas argued that law, by its nature, must be promulgated to be binding. This follows from the fact that law is intended to direct individuals toward the common good, and to do so, it must be made known to them (Summa Theologica, 1a2ae. 90, 4). Ignorance of the law, therefore, may excuse one from the obligation to follow it, unless that ignorance is culpable—meaning it is the result of negligence or willful disregard.


The proclamation of law is not merely a formality but a necessary step in ensuring that individuals are aware of their duties and the standards by which their actions will be judged. Without this proclamation, law loses its power to guide and regulate behavior effectively.



Differentiating the Kinds of Law


Law is not monolithic; rather, it encompasses various forms, each with its sphere of influence and authority. Aquinas identified four primary kinds of law: eternal law, natural law, human law, and divine law. Each of these serves as a measure or rule in different contexts, and together they form a comprehensive framework for understanding the moral and legal obligations of individuals.


Eternal Law: The Divine Principle of the Universe


Eternal law, as the name suggests, is the principle that lies at the very heart of the universe, governing all things. It is the divine reason by which God rules and orders the universe. Aquinas described eternal law as the idea in the mind of God that serves as the blueprint for all creation (Summa Theologica, 1a2ae. 91, 1). It is the source from which all other laws derive their authority and rationality. Because it resides in the eternal mind of God, it is unchanging and has been set in place from eternity.


Eternal law is not only the foundation of the physical order of the universe but also the moral order. All things that exist and all laws that govern them share in the eternal law to the extent that they align with right reason. This alignment with right reason is what gives human laws their legitimacy and binding force.


Natural Law: The Human Participation in Eternal Law


Natural law is the communication of eternal law to rational creatures. It is the way in which human beings, through the use of reason, participate in the eternal law. Natural law is not something external imposed on humanity; rather, it is inscribed in the very nature of human beings. It is the "law written on the heart" that Paul speaks of in Romans 2:15, which gives all people an innate sense of right and wrong.


Aquinas emphasized that natural law is the light of reason by which we discern what is good and what is evil (Summa Theologica, 1a2ae. 91, 2). It is not arbitrary but is rooted in the rational and moral nature of human beings. To act in accordance with natural law is to act in harmony with one's true nature as a rational and moral being. Conversely, to violate natural law is to act against one's nature, leading to moral disorder and, ultimately, unhappiness.


However, natural law is not the ultimate measure; it is subordinate to eternal law. Human reason, while capable of discerning the precepts of natural law, is not infallible and must align itself with the eternal law to ensure that actions are truly good. When human acts are in harmony with the order of reason and eternal law, they are right; when they deviate from this harmony, they are wrong (Summa Theologica, 1a2ae. 21, 1).


Human Law: The Practical Application of Natural Law


Human law, also known as positive or civil law, is the attempt by human reason to apply the general principles of natural law to the specific circumstances of society. It is the process by which practical reason takes the broad directives of natural law and formulates concrete laws that govern social behavior (Summa Theologica, 1a2ae. 91, 3). Human law is, therefore, a particularization of natural law, adapted to the needs and conditions of a given society.


Human laws can be seen as conclusions drawn from the general principles of natural law. For example, the natural law precept "do not harm others" may be particularized into the human law "do not kill." Some human laws are direct conclusions from natural law, while others are more specific applications that may vary depending on circumstances. For instance, natural law dictates that wrongdoers should be punished, but the exact nature of the punishment may be determined by human law based on what is most fitting for the community.


Not every human law, however, is necessarily just or valid. A law has the force of law only if it serves the common good and aligns with the principles of natural law. Laws that violate natural law or fail to promote the common good do not have true legal authority, even if they are enforced by a government. Aquinas noted that human law should not attempt to forbid all vices, as it is impossible to legislate perfect virtue. Instead, human law should focus on prohibiting the gravest offenses that threaten social stability and the common good (Summa Theologica, 1a2ae. 96, 2).


Divine Law: The Guidance Toward Eternal Good


Divine law differs from natural law in its purpose and scope. While natural law is accessible to all human beings through reason and governs temporal matters, divine law is revealed through Scripture and is directed toward leading individuals to God. Divine law is concerned with eternal rather than temporal good, and it is binding on those who belong to the church, guiding them toward salvation and a deeper relationship with God.


Divine law is given specifically to believers and is designed to bring them into conformity with God's will. It is not limited to the moral principles accessible through reason but includes specific commands and prohibitions that are revealed through Scripture. For example, the moral law given in the Ten Commandments is an expression of divine law, as is the teaching of Jesus in the Sermon on the Mount.


Aquinas pointed out that divine law, unlike natural law, can change because it is based on God's will rather than His unchanging nature. This is evident in the transition from the Old Testament to the New Testament, where certain ceremonial and judicial laws were abrogated or fulfilled in Christ (Summa Theologica, 2a2ae. 57, 2). However, the moral principles underlying divine law remain consistent, as they reflect the character of God.



The Purpose and Function of Law in Human Life


The purpose of law, in its various forms, is to regulate human activity in accordance with God's will and the common good. Each kind of law—eternal, natural, human, and divine—has its specific sphere of influence and contributes to the overall order and harmony of creation.


Promoting Friendship and Community


One of the key purposes of law is to promote friendship and social harmony. Just as human law is intended to foster peaceful relationships among individuals within a society, divine law is designed to establish and nurture the relationship between humanity and God. Aquinas noted that law is essential for maintaining right relationships, as it provides the standards by which individuals interact with one another in a just and equitable manner (Summa Theologica, 2a2ae. 99, 2).


The promotion of friendship through law is not merely a utilitarian goal but is rooted in the very nature of God, who is love. The law of love, as articulated by Jesus, sums up all other laws: "You shall love Jehovah your God with all your heart and with all your soul and with all your mind. This is the great and first commandment. And a second is like it: You shall love your neighbor as yourself" (Matthew 22:37-39). The law of love is the highest expression of God's will and serves as the foundation for all other laws.


Curbing Evil and Protecting Society


Another purpose of law is to curb evil and protect society from harm. While the primary goal of law is to guide individuals toward the good, it also serves a secondary function of penalizing those who disobey and thereby safeguarding the community. This is true not only of human law but also of divine and natural law. Sanctions and penalties are necessary to maintain order and prevent the spread of vice and corruption (Summa Theologica, 2a2ae. 68, 1).


The role of law in curbing evil is particularly important in a fallen world where human beings are prone to sin and wrongdoing. By establishing clear standards of right and wrong and enforcing them through appropriate penalties, law acts as a deterrent to immoral behavior and helps to preserve the common good.


Achieving the Common Good


The ultimate purpose of law is to achieve the common good, which is the well-being of the entire community. The common good is not merely the sum of individual goods but the flourishing of the community as a whole. Human laws, therefore, must be crafted with the common good in mind, ensuring that they promote justice, peace, and the welfare of all members of society.


Aquinas recognized that it is impossible to create laws that account for every possible situation or exception. Therefore, legislators must focus on what happens in the majority of cases and frame laws accordingly (Summa Theologica, 2a2ae. 120, 1). However, when a specific case arises where following the letter of the law would result in harm rather than good, equity—a principle of fairness that seeks to uphold the spirit rather than the letter of the law—should prevail. This approach ensures that the law serves its true purpose of promoting the common good, even in exceptional circumstances.



The Hierarchy of Laws and Their Conflicts


In a world governed by multiple kinds of law, conflicts can sometimes arise between different laws or between the letter and the spirit of the law. When such conflicts occur, there is a hierarchy of laws that determines which law takes precedence.


The Priority of Natural Law


Natural law, being a direct participation in the eternal law, holds a higher place in the hierarchy of laws than human law. While human laws are necessary for regulating society, they are not infallible and must yield to natural law when there is a conflict. For example, the natural law precept "do not harm others" may override a human law that commands the return of a borrowed weapon to someone in a murderous rage. In such cases, the virtue of justice or equity demands that the higher law of natural law be followed (Summa Theologica, 2a2ae. 120, 1).


This principle of prioritizing natural law over human law is crucial in ensuring that human laws do not become instruments of injustice. When human laws are unjust or contrary to the common good, individuals are not morally obligated to obey them. Instead, they must follow the higher law of natural law, which reflects the unchanging moral order established by God.


The Unchanging Nature of Natural Law


Natural law, unlike human or divine law, is based on the unchanging nature of God and therefore cannot be altered. While divine law may change according to God's will—as seen in the transition from the Old Testament to the New Testament—natural law remains consistent across time and cultures. This consistency is rooted in the fact that natural law reflects the very character of God, who is the same yesterday, today, and forever (Hebrews 13:8).


Because natural law is unchanging, it provides a stable foundation for moral reasoning and legal systems. It serves as the ultimate measure by which all other laws are judged, ensuring that they align with the eternal moral order. When conflicts arise between changeable laws (such as human or divine law) and the unchanging natural law, the latter takes priority, as it is rooted in the very nature of God.



The Relationship Between Letter and Spirit of the Law


In addition to the hierarchy of laws, it is important to consider the relationship between the letter and the spirit of the law. The letter of the law refers to the explicit wording of legal statutes, while the spirit of the law refers to the underlying principles and intentions that the law seeks to uphold.


Christian thinkers have long recognized that there are situations where following the letter of the law may not achieve justice or the common good. In such cases, the spirit of the law should take precedence, as it better reflects the true purpose of the law. Aquinas noted that the judgment that the letter of the law is not to be followed in certain circumstances is not a criticism of the law but an appreciation of the particular situation that has arisen (Summa Theologica, 2a2ae. 120, 1).


This distinction between letter and spirit is important in preventing legalism, where the strict adherence to the letter of the law leads to injustice or harm. Instead, equity should guide the application of the law, ensuring that it serves its intended purpose of promoting the common good and upholding moral principles.



The Role of Natural Law in Christian Apologetics


Natural law plays a significant role in Christian apologetics, particularly in discussions about morality, justice, and the basis for ethical behavior. The concept of natural law provides a bridge between believers and non-believers, as it appeals to a universal moral order that is accessible to all human beings through reason.


The Universality of Natural Law


One of the key strengths of natural law is its universality. Natural law is not dependent on special revelation or religious belief; it is accessible to all people, regardless of their faith or background. This universality makes natural law a powerful tool in apologetics, as it provides a common ground for discussing moral issues with those who may not share the same religious beliefs.


Romans 2:15 states that God's moral law is written on the hearts of all people, giving them an innate sense of right and wrong. This innate moral knowledge is a reflection of the natural law that God has inscribed in human nature. Even those who do not acknowledge God can recognize basic moral principles, such as the prohibition against murder or the duty to care for others.


Addressing Moral Relativism


Natural law also provides a strong response to the challenge of moral relativism, which denies the existence of objective moral standards. Moral relativism asserts that moral values are subjective and vary from culture to culture or from person to person. In contrast, natural law affirms that there are objective moral truths that are universally binding on all people, regardless of their individual beliefs or cultural norms.


By appealing to natural law, Christians can argue that certain moral principles, such as justice, honesty, and compassion, are not merely social constructs but are rooted in the very nature of humanity as created by God. These principles are self-evident and can be recognized through reason, even by those who do not have access to special revelation.


Engaging with Secular Thinkers


Natural law provides a framework for engaging with secular thinkers and philosophers who may not accept the authority of Scripture. Because natural law is grounded in reason and accessible to all people, it can be used to build a case for moral truths that are consistent with biblical teachings but do not require an appeal to Scripture.


For example, Christian apologists can use natural law to argue for the sanctity of human life, the importance of marriage and family, and the necessity of justice and mercy in society. These arguments can resonate with those who value reason and ethical principles but may not share the same religious convictions.


The Challenge of Suppressing Conscience


While natural law provides a universal moral standard, it is important to recognize that individuals can suppress their conscience and become morally dull. The apostle Paul warns in Romans 1:18-32 about those who suppress the truth in unrighteousness, leading to a darkened mind and a life of moral decay.


This suppression of conscience is a significant challenge in a fallen world, where sin distorts human reason and moral judgment. While natural law is written on the hearts of all people, sin can obscure this moral knowledge and lead individuals to act contrary to their true nature. This is why the proclamation of the gospel and the work of the Holy Spirit are essential in bringing people to a true understanding of God's moral law and leading them to repentance.



The Integration of Natural and Divine Law


Finally, it is important to consider the relationship between natural law and divine law in the life of the believer. While natural law provides a universal moral standard accessible to all people, divine law, as revealed in Scripture, offers a fuller and more specific understanding of God's will for humanity.


For believers, natural law and divine law are not in conflict but are complementary. Natural law provides the foundation for moral reasoning, while divine law offers the specific guidance and commands needed to live a life pleasing to God. The integration of these two forms of law is essential for a holistic understanding of morality and ethics.


In summary, natural law is a fundamental concept in Christian thought, providing a universal moral standard that is accessible to all people through reason. It reflects the eternal law of God and serves as the basis for human law and ethical behavior. By understanding and applying natural law, believers can engage with the world in a way that upholds justice, promotes the common good, and bears witness to the truth of God's moral order.


About the Author

EDWARD D. ANDREWS (AS in Criminal Justice, BS in Religion, MA in Biblical Studies, and MDiv in Theology) is CEO and President of Christian Publishing House. He has authored over 220 books. In addition, Andrews is the Chief Translator of the Updated American Standard Version (UASV).


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