Natural Law Theory: A Case for Objective Morality in a Secular Age

What can a Christian do when facing modern-day moral issues that the Bible does not directly address? Furthermore, how can Christians engage in current public moral debates with those who do not share our conviction in the authority of the Bible? The natural law theory of ethics provides a solution.

Although natural law theory offers immense insight for Christian moral reasoning, many Christians are unfamiliar with it. In this article, I explain why every Christian should know the natural law theory of ethics. In short, I contend that Christians who adopt natural law ethical reasoning will be more effective at applying the Bible’s principles to moral issues and questions.

What is natural law theory?

Natural law

Before considering natural law theory, let us first attend to what is meant by natural law.

David VanDrunen defines the natural law as “the law of God made known in the created order, which all human beings know through their physical senses, intellect, and conscience, although they sinfully resist this knowledge to various degrees.”¹

Through the natural law, people can discern basic moral goods, also called the basic human goods. They are basic because they are intrinsically valuable and self-evident. They are good because they secure human flourishing. Natural law philosopher John Finnis identifies seven basic human goods:

1. Life
2. Knowledge
3. Play
4. Aesthetic experience
5. Sociability (friendship)
6. Practical reasonableness
7. Religion²

Though not moral obligations themselves, they serve as foundations for moral duties because pursuing them leads to human flourishing.

Natural law theory

Natural law theory then aims to systematize God’s natural law into an ethical framework.

According to natural law theory, we derive moral precepts from the above basic human goods. Actions and virtues that promote and preserve the basic human goods are morally right, whereas actions that negate them are immoral.

Actions and virtues that promote and preserve the basic human goods are morally right, whereas actions that negate them are immoral.

For example, murder is immoral because it violates the basic good of life. Even without the Bible, people recognize murder is immoral. It violates the natural moral order, wounds the conscience, is against reason, and negates human flourishing. A Christian can condemn murder both because Scripture condemns it and because it violates the natural law written on every heart.

Genesis 1:26–27 reveals that God created people in his own image. God also created human nature to function in ways specifically good for humans. Natural law theory argues that what is moral aligns with what fulfills human nature’s good ends and purposes as God intended them.

Additionally, according to Romans 2:14–15, God gave every human a conscience to perceive his moral truth. The conscience functions as a type of moral sensor in partnership with reason that affirms or condemns these actions.

Thus, natural law theory is an ethical framework that affirms:

• Objective moral laws exist.
• God has encoded them within the natural order, forming a natural law.
• Humans have the rational capacities to discern these natural laws.
• God designed human nature so that aiming at these laws secures human good.
• All people are accountable to God for obeying these universally knowable moral laws.

Types of law in natural law theory

Finally, classical natural law theory distinguishes four kinds of moral law (see Aquinas, Summa Theologiae I–II, Q. 91, A. 1–6).

1. Eternal law: God’s secret will and counsel for his divine governance (cf. Eph 1:11).
2. Divine law: The revealed portion of God’s eternal law made known through Scripture (cf. Deut 29:29).
3. Natural law: The revealed portion of God’s eternal law made known through the natural order of the universe, discernable through reason and conscience. It is the moral law written on the heart (cf. Rom 2:15).
4. Human law: Societal laws derived from the natural law (and sometimes divine law) to promote civil order and flourishing.

Positive law refers to the legal codes enacted by human governments. Natural law theory holds that positive laws are legitimate when derived from the natural law.³

Natural law reasoning undergirds human legislation, even when lawmakers are unaware of it (Summa I–II, Q. 95, A. 2). For example, setting speed limit laws reflects the intuitive effort to protect the basic good, life.

What is the history of natural law theory?

From Aristotle to Aquinas

Thomas Aquinas (1225–1274) is the father of natural law theory, but the theory’s philosophical roots trace back to Aristotle (384–322 BC). Aristotle taught in his Nicomachean Ethics that every creature has a distinct nature with a corresponding ultimate purpose (telos). Aristotle believed human telos to be happiness (eudaimonia), which is achieved through virtuous actions consistent with human nature.

Aquinas integrated Aristotle’s philosophical teleology with Christian theology in his Summa Theologiae and developed the natural law theory. He affirmed that humans, made in God’s image (cf. Gen 1:26, 27), are rational creatures. Therefore, people can discern moral norms that align with human nature’s divinely given telos.

Aquinas surmised that moral norms flow from God’s good nature and are encoded in creation. God has given people synderesis (συνείδησις, “conscience”), a divinely implanted character disposition that enables people to discern good and evil (Summa I, Q. 79, A. 12). Aquinas also first articulated the four categories of moral law, listed above.

Aquinas theorized that through the exercise of reason, people instinctively know we should do good and avoid evil (Summa I–II, Q. 94, A. 2). He called this the first principle of practical reason, even though the effects of sin cause inconsistent adherence. From the first principle, people discern that to do good, they must uphold the basic human goods.

Aquinas identified five basic human goods (Summa I–II, Q. 94, A.2–4).

1. God, directing human reason towards our Creator, finding fulfillment in him
2. Life, preservation, protection, and flourishing of human life
3. Family, encompassing marriage, sexual union, procreation, and child-rearing
4. Truth, valuing truth over falsehood and pursuing knowledge over ignorance
5. Reason, properly exercising rational faculties

Protestantism and natural law theory

Roman Catholicism has embraced natural law theory for centuries. Up until the twentieth century, Protestantism also broadly accepted natural law reasoning. Reformers like John Calvin and Martin Luther affirmed the principles of natural law,⁴ which were later re-articulated within Neo-Calvinism’s concept of common grace.

Modern Protestants grew skeptical, believing natural law theory undermines biblical authority and underestimates the noetic effects of the fall.⁵ They perceive sola scriptura and total depravity as inconsistent with the natural law.

Despite these modern concerns, Protestants—such as G. C. Berkouwer—point out that the Reformers largely agreed with natural law reasoning.⁶ Aquinas himself even argued that the natural law is limited, and that special revelation is required to teach all of God’s law (Summa I–II, Q. 91, A.4). Thus, natural law and special revelation work in harmony, not in competition.

Natural law theory today

How do we see natural law theory being received in contemporary times?

As we saw, Aquinas’s classical natural law version rooted morality in God and his creation of human nature. The current new natural law theorists, such as John Finnis, Robert P. George, and Francis Beckwith, recast natural law in philosophical ways that stretch beyond theological commitments. They attempt to maintain the rational credibility of natural law theory among secular thinkers while affirming moral realism.

Natural law theory is also currently undergoing a revival in Protestant scholarship, most notably in evangelicalism. Scholars such as David VanDrunen, Andrew T. Walker, and J. Daryl Charles are examples.

Finally, we should note that natural law tradition gave rise to the modern idea of natural rights. Natural law thinkers reason that rights derive from the basic human goods. Rights are meant to protect these goods. Natural law reasoning then is an influential voice in the debate over the origin and nature of human rights.

Does natural law theory accord with Scripture?

While the Bible never mentions natural law theory, it clearly teaches the existence of moral law encoded in creation and human conscience.

We find the natural law either taught or implied in the following ways.

1. The gentile law-keepers (Rom 1–2)

Paul gives the clearest case in Scripture for natural law in the first two chapters of Romans. In Romans 1:18–20, he says that ungodly gentiles actively “suppress [κατέχω] the truth” they already know. They know God’s moral standards through the created order (natural revelation), thus leaving them “without excuse” for their unrighteousness. In Romans 1:32, Paul adds that they intuitively recognize God’s righteous standards yet willingly rebel against them.

In Romans 2:12–15, Paul explains that even gentiles who never knew the Mosaic law (divine law) still perish according to its condemnation. They instinctively, “by nature [φύσις],” know God’s moral demands. Though lacking the clarity of the written Mosaic law, these gentiles have its moral essence “written on their hearts.” God gave all people a conscience (συνείδησις) that testifies to their hearts, either accusing or excusing their actions.

God can hold all people accountable because the natural law teaches the essence of the divine law externally through creation and internally through conscience.

2. Creation ordered towards the good

Genesis 1 reveals that God created the world with a natural orderliness toward goodness. After each creative act, God declared that it was “good” (טוֹב). The Hebrew word טוֹב suggests that what God made was not only pleasant but properly ordered to its intended function.

In Genesis 2:18, God declared Adam’s lack of a helpmate “not good” (לֹא־טֹ֛וב). God created Eve and established marriage, sexual union, and procreation as parts of his naturally good order. These actions reveal that creation possesses built-in orderliness toward goodness—a natural law.

A Logos Bible Word Study on the Hebrew word טוֹב (“good”).

3. Pre-Mosaic moral accountability

After humanity’s fall into sin, God held people morally accountable before he gave the Mosaic law (see Rom 5:12–14; cf. Rom 5:20–21; Gal 3:19). Therefore, a natural law of morality existed that contained enough moral knowledge to hold violators culpable before God.

In Genesis 15:16, God says he will judge the Amorites for their iniquity. Thus, God judged pagan nations according to a moral standard they could naturally know. Likewise, Sodom and Gomorrah’s “very grave” sins (Gen 18:20) brought about God’s judgment. Their sexually deviant, violent sins reflected an “unnatural” desire (cf. Jude 7), suggesting they intuitively knew it was immoral.

These examples demonstrate that God expected pagans to live morally because God had revealed sufficient moral truth to them through nature and conscience.

4. The morality of the Ten Commandments

The Ten Commandments (Exod 20:1–17) are an instance of the divine law articulating natural law moral precepts. The moral precepts undergirding the Ten Commandments were already moral precepts before they became part of special revelation. Acts like murder, theft, adultery, and lying were already immoral before God codified them in writing.

Further, the Ten Commandments aim to protect the basic human goods, such as:

• God (no other gods, no idols, do not take God’s name vainly, keep sabbath)
• Family (honor one’s parents and one’s marriage)
• Life (don’t murder)
• Community (no stealing, false testimony, or coveting)
• Truth (same as above)

In sum, the Bible presents a case for the existence of natural law. It maintains God’s good order in nature and that this is knowable by all. It contains enough moral data to hold all people morally accountable to God.

FAQs about natural law theory

1. Does sin render the natural law theory ineffective?

Sin causes people to ignore the natural law’s demands intentionally, but sin does not make people ignorant of them.

Romans 2:14–15 makes clear that in our post-fall era, God holds all people accountable for violating the natural law revealed through conscience.

2. If natural law theory is true, why are people not more moral?

Although sin leads people to suppress the moral truth they know, humanity still evidences moral awareness. Societies often establish governments and laws based on the moral commitment to promote the common good.

I believe that if not for God’s natural law bestowing a moral common grace, no stable society could have ever formed.

3. If natural law theory is true, why is there disagreement over the basic human goods?

While natural law theorists may differ in their lists of basic human goods, they all agree that they exist. Debates arise over the categorization of certain moral goods. For instance, all theorists agree that justice is an essential moral good. But there is disagreement over whether justice is a primary moral good or a secondary good dependent on another, primary one.

Why does natural law theory matter?

There are several key applications of natural law theory for Christians.

1. Natural law theory enhances Christian ethics

Natural law theory enhances Christian ethics by demonstrating how the Bible’s moral principles apply to extrabiblical issues. Natural law reasoning shows that Christian morality rests on rational, universally knowable moral truths, not merely on faith-based commitments. It shows the world that Christian ethics apply to everyone, not just Christians.

2. Natural law theory equips Christians to engage the public square

Western societies have in many respects abandoned a shared morality that the Bible informed. Natural law theory helps meet this state of affairs. It equips Christians to address moral issues in the public square among those with secular minds who deny the Bible’s authority.

Natural law theory equips Christians to address moral issues in the public square among those with secular minds.

Natural law reasoning shows Christians how to argue for morality in the public square rationally and intelligently, not just theologically.

3. Natural law informs our moral reasoning

Consider the issue of lying. Natural law reasoning asserts that lying is immoral because it denies truth, a basic human good. Truth is essential for human relationships and communities to flourish. Human reasoning and our conscience instruct us that lying is contrary to morally sound behavior.

Gene editing, though not directly addressed in the Bible, can be evaluated with natural law reasoning. Its morality depends on intention, process, and outcome. Gene editing technology can be used to treat genetic diseases. This intention upholds the basic human good of life and is therefore moral.

However, gene editing technology also permits the preferential genetic design of babies during embryonic development. The intention behind designing babies’ traits violates the basic goods of God and life. It usurps God’s sovereign place as the one who makes people in his image. It violates life because it reduces people to a customizable commodity. A case can also be made that it violates human rights by undermining natural human dignity and equality.

Conclusion

Natural law theory is an ethical theory that uses the natural law of God to inform moral reasoning. It posits the existence of objective moral principles knowable to every person since God has encoded them in his creation. God has designed human nature in such a way that people intuitively know the moral norms necessary for human goodness. Therefore, natural law theory posits that through reasoning and conscience, every person knows what they morally ought to do.

Natural law theory has biblical warrant and justification. The reality of a natural moral law that God expects all people to obey is illustrated throughout Scripture. Most notably, Paul argued that the basis upon which God judges gentile pagans is that they deny his natural law of morality that they knew through conscience.

Proponents of natural law theory stand in good company with many luminaries from church history. Aquinas was its father, but it has been carried forward in both Catholic and Protestant streams of Christianity. To this day, natural law theory is an influential voice in Christian ethics, moral reasoning, and human rights debates.

Natural law theory matters for believers today because it:

• Effectively applies biblical principles to complex issues
• Strengthens our moral witness for Christ
• Shows secular listeners that Christian values are rational and intuitive
• Gives us a compelling moral voice in the public square

Dustin Burdin’s recommended books for further study

• George, Robert P. In Defense of Natural Law. Oxford University Press, 2004.

Additional resources on natural law

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