Religious vs. Secular Natural Law

Introduction

Welcome to your next lesson. In our previous explorations, we've seen how natural law theory provides a foundation for justice derived from nature and reason. We started with Aquinas, who grounded this law in a divine cosmic order, and then analyzed Locke, who used natural law to construct a powerful theory of individual rights, particularly property rights. Locke represents a pivotal moment: while he invokes God, his system of rights derived from reason became a cornerstone of secular liberal thought.

This lesson builds directly on that tension. Our learning outcome is to compare religious natural law (grounded in divine order) with secular natural law (grounded in rational human nature). We will dissect the fundamental assumptions of each approach, exploring how their different starting points—one in theology, the other in philosophy—lead to distinct conceptions of law, morality, and the human purpose. For your interest in the "architecture" of justice systems, this distinction is crucial, as it represents a foundational split in the blueprints for Western legal and moral thought.

1. The Two Historical Fountains of Natural Law

The idea of a "natural law" has two major streams of influence flowing from the ancient world, and their differences set the stage for the religious/secular distinction. One stream is rooted in Judeo-Christian theology, and the other in Greco-Roman philosophy, particularly Stoicism.

John Milbank, a contemporary theologian, provides a concise history of these two origins.

As Milbank outlines, the two foundational traditions are:

• The Biblical/Philonic Tradition (Religious): This view, originating with thinkers like Philo of Alexandria who merged Hebrew scripture with Greek philosophy, sees the cosmos as governed by a personal, transcendent God. Natural law is an expression of God's will and eternal law. In this tradition, revealed law (like the Ten Commandments) is not separate from natural law but is its clearest and most perfect articulation. The world is seen as a megalopolis—a single great city under divine rule, implying a "politicization of nature."

• The Stoic Tradition (Proto-Secular): The Stoics also saw the world as a single cosmopolis, but their conception of divine will was less about a personal, transcendent God and more about an impersonal, immanent force of reason (logos) or fate that pervades the universe. For the Stoics, natural law's dictates are intelligible without reference to citizenship in any particular city or revealed text. This "naturalization of politics," as Milbank puts it, laid the groundwork for thinkers like Cicero, Grotius, and Locke to develop theories of natural rights and international law focused on protecting the individual, largely independent of a specific theological framework.

This ancient fork in the road—one path starting from divine revelation, the other from immanent universal reason—defines the core of our comparison.

2. The Religious Model: The Thomistic Synthesis

The most sophisticated and influential model of religious natural law is that of Thomas Aquinas. He masterfully synthesized Christian theology with Aristotelian philosophy to create a comprehensive framework where nature and grace, reason and faith, all have their place.

To understand this architecture, we'll use a helpful metaphor introduced by philosopher J. Budziszewski.

Budziszewski's metaphor illustrates the Thomistic system perfectly:

• The First Floor (Nature): This represents the domain of natural goods and natural law. These are truths accessible to all human beings through the use of their natural reason. This includes basic moral principles like "do good and avoid evil," the wrongness of murder, and the goods of social life. The state, as a natural institution, has authority on this floor—its proper role is to enforce the natural law to promote earthly flourishing.

• The Second Floor (Grace): This represents the supernatural goods of salvation and eternal life with God. These truths are not accessible by reason alone; they require divine revelation (Scripture) and the gift of faith. The Church, not the state, is the authority on this floor.

This two-story model is the essence of the religious conception: reason can get you on the first floor, but it's an incomplete picture. For the religious natural lawyer, human nature is fallen and our reason is "slippery" (what Budziszewski calls the "basement" of the house). Therefore, to fully understand our purpose and fulfill the law, reason must be aided by divine grace and guided by revelation. Natural law is a participation in God's eternal law, but divine law is a more perfect guide.

3. The Secular Turn: Reason Alone

Beginning in the early modern period, especially in the wake of the devastating Wars of Religion, thinkers sought a foundation for law and morality that did not depend on a specific, contested theological doctrine. This spurred the development of secular natural law theories.

Let's clarify what this "secular" turn entails and look at a modern example.

As the video explains, secular natural law attempts to ground moral and legal principles in philosophy alone, using arguments from reason that are accessible to anyone, regardless of their religious beliefs.

A key figure here is the Dutch jurist Hugo Grotius (1583-1645). He famously argued in De Jure Belli ac Pacis (On the Law of War and Peace) that the principles of natural law would have "a degree of validity" etiamsi daremus non esse Deum—"even if we were to grant that there is no God." This was not an atheistic statement; rather, it was a methodological move to establish a basis for law (especially international law) that could bind all people, regardless of their faith.

The video's introduction to John Finnis (1940-) shows how this project has evolved. Finnis's "New Natural Law" theory is a sophisticated contemporary example.

• It does not begin with a theological concept of a human telos (end/purpose) given by God.
• Instead, it starts by identifying several "basic human goods" that are self-evidently valuable and pursued for their own sake: life, knowledge, play, aesthetic experience, friendship, practical reasonableness, and religion (in the sense of considering ultimate questions).
• Principles of morality and justice are then derived as the requirements of "practical reasonableness" in the pursuit of these goods. For example, one must have a coherent plan of life, not arbitrarily discount certain goods or people, and favor the common good of one's communities.

This is a secular theory because it grounds itself in an analysis of human reason and action, not in divine command or revelation.

4. Is the "Secularization" Story Too Simple?

The clean narrative of a "switch" from religious to secular natural law is, of course, an oversimplification. Your interest in orthogonal perspectives will appreciate the nuances here. The historical reality was a complex interplay of traditions.

This reading challenges the simple narrative in two key ways:

1. Secularization can mean different things: It wasn't necessarily a deliberate rejection of God. It could be an unintended long-term effect, or a jurisdictional shift where jurists, rather than theologians, became the primary interpreters of natural law. This reframes it as a change in institutional authority, a theme central to this course.
2. Parallel Traditions Existed: While thinkers like Grotius were developing a more universalist, reason-based framework, a robust "Hebraist natural law" tradition flourished. These scholars looked to the ancient Hebrew polity and Mosaic law not just as revealed divine commands, but as a source of universal political and legal wisdom, often seeing it as older and more profound than Roman law.

This shows that the "secular" turn was not the only story. Different groups continued to ground their understanding of natural law directly in sacred texts, offering an alternative model of societal organization.

Conclusion

Today we have compared the two great traditions of natural law. We've seen that they diverge on the ultimate source and justification of moral principles.

Key Takeaways:

• Religious Natural Law (e.g., Aquinas) grounds justice in divine order. Natural law is humanity's participation in God's eternal, rational plan for the cosmos. Its principles are discoverable by reason, but this reason is considered fallible and incomplete without the aid of divine grace and revelation (Scripture). The ultimate human purpose (telos) is supernatural: union with God.
• Secular Natural Law (e.g., Grotius, Finnis) grounds justice in rational human nature. Moral principles are derived from reason alone, whether by analyzing the logical requirements for social life or identifying self-evident "basic goods." It seeks to provide a universal foundation for law that is independent of specific theological commitments. The human purpose is typically understood in this-worldly terms of flourishing.
• The historical shift from the former to the latter, often termed "secularization," is not a simple story of abandoning religion, but a complex process involving methodological shifts, changes in institutional authority, and the co-existence of competing traditions.

Ultimately, the choice between these foundations is a choice about the nature of reality itself: Is the moral order inscribed in the cosmos by a divine legislator, or is it a structure that human reason builds to make sense of its own condition?

Preview of the next lesson:

Having examined how natural law can be derived from both divine order and secular reason, we will conclude our module on Classical and Natural Law by exploring what happens when these principles are put into practice. The final lesson will ask you to apply natural law reasoning to evaluate conflicts between positive law (the law of the state) and moral law. This will bring these abstract principles to bear on concrete legal and ethical dilemmas.