ABSTRACT: When some hear the phrase “natural law,” they think of animal instinct, survival of the fittest, or the laws of physics. In Christian history, however, natural law refers to basic moral principles woven by God into the fabric of creation. Political laws derive from the natural law, and they carry the force of God’s standard only insofar as they accurately reflect nature. The biblical writers also assume the relevance of natural law, both in establishing proper customs and testifying to our need for forgiveness. Even still, nature cannot teach us where our deepest hope lies: not in the law itself, but in the Christ who saves the law’s transgressors.

The issue of natural law may confound the people . . . you and I at least know what we are talking about here. . . . You know and I know it is a big, big deal. (Joe Biden, from 1991)

I have no idea what he was talking about. (Clarence Thomas, from 2020)¹

Discussions over natural law can be just as confusing within the church as they are in American politics, demonstrated by the two quotes above. Some hold strong feelings about natural law, whether it exists at all and, if so, what it teaches. Others argue that it’s a foreign influence fundamentally opposed to biblical revelation. Others still try to understand what natural-law thinkers are even talking about.

In this essay, I would like to help us understand the key terms and concepts involved in a philosophy of natural law. I discuss what these terms and concepts mean and how they can be used, and then I discuss a few passages of the New Testament that use the logic, and even occasionally the language, of natural law. The Bible does indeed show that nature can teach, and this is important. But just as importantly, the Bible shows there are some lessons that nature cannot teach, or at least not well enough. So, I conclude with a look at the limits of natural law.

What Is Natural Law?

In the twenty-first century, the average person hears nature and thinks of modern biology or even zoology. Natural law, then, is assumed to be something like animal instinct. Worse, some might interpret it along the lines of the survival of the fittest, thus making natural law merely a contest of appetite and might. This is not what natural law meant in older Christian thought. Another misconception is that natural law is an invisible textbook in the sky. Most humans have “always known” certain things, and so the assumption is that if we simply go back to the appropriate time in history or look at the appropriate cultures, we will find the true list of moral laws that can be our standard. This is a sophisticated trump card, but it’s a trump nonetheless.

More accurately, natural law is a method of moral reasoning. Instead of only discussing a positive set of do’s and don’ts, natural law is instead an attempt to locate and demonstrate the rational foundation for a particular duty or prohibition. Thomas Aquinas calls it “participation of the eternal law in the rational creature.”² More properly, it is an exercise in reasoning from the most basic rational moral principles applied to various moral questions, eventually leading to specific legal cases. Considered wholly on its own, natural law is the earliest philosophical stage of this exercise. As we move from speculative argument into practical application, we quickly move into politics — not the sometimes-unseemly business of cutting deals or building a coalition, but rather the art of ordering human society. Even the early stages of natural-law reasoning, however, imply the need for further application, since the law imprinted in our nature causes various inclinations.³

Sixteenth-century Reformed theologian Franciscus Junius explains the natural law this way: “The natural law is that which is innate to creatures endowed with reason and informs them with common notions of nature, that is, with principles and conclusions adumbrating the eternal law by a certain participation.”⁴ While impressively tight, this is a loaded definition. Innate reason informs the creature by way of common notions that highlight both principles and conclusions. This means that the applications and eventual positive laws are themselves contained, at least in seed form, in the basic teaching given by the natural law.

But this still requires a process of argument. As Junius goes on to note, the natural law has never been “equally perceived by all.”⁵ Human sinfulness tends to distort or suppress the natural law, and error increases as men move from general principles to particulars.⁶ So natural-law thinking has always included the need for teaching, as well as social and moral formation in particular settings.

“The content of the natural law can be explained most basically as ‘seek the good and avoid the evil.’”

The content of the natural law can be explained most basically as “seek the good and avoid the evil.”⁷ Christian authors have universally argued that this also implied the moral content of the Ten Commandments. John Calvin writes, “The very things contained in the two tables are, in a manner, dictated to us by that internal law, which, as has been already said, is in a manner written and stamped on every heart.”⁸ The Westminster Confession of Faith states, “This law [given in Eden], after his fall, continued to be a perfect rule of righteousness; and, as such, was delivered by God upon Mount Sinai, in ten commandments, and written in two tables.”⁹ The Confession, citing Matthew 22:37–40, explains that this law can be understood as teaching our duty toward God, “Love the Lord your God,” and our duty toward our fellow man, “Love your neighbor as yourself.” This means that “the good” that we are seeking is the love of God and then, following that, the love of man, and “the evil” that we are avoiding is the opposite.

Human Law, Custom, Decorum

So then, the natural law, in its most basic form, is the root understanding of goodness and the inclination toward actions that are consistent with that goodness. However, to go much further, humans need actual legislation, the passing and enforcing of positive laws, as well as moral formation through social relationships and teaching.

The most basic distinction in this discussion is between natural law and human law. Thomas Aquinas explains it this way:

Just as, in the speculative reason, from naturally known indemonstrable principles, we draw the conclusions of the various sciences, the knowledge of which is not imparted to us by nature, but acquired by the efforts of reason, so too it is from the precepts of the natural law, as from general and indemonstrable principles, that the human reason needs to proceed to the more particular determination of certain matters. These particular determinations, devised by human reason, are called human laws.¹⁰

This means that natural law, as such, consists of the moral principles themselves, known innately and immediately, whereas the “particular determinations” of a person or group applying those principles in conversation with other sciences is “human law.” To call it human law is not to denigrate such laws, but it is to admit that they are more particular and more varied between peoples.¹¹ It is also to acknowledge that human law can be changed as necessary.¹² Importantly, the distinction between natural law and human law also explains the limits of human law. If a human law is inconsistent with the natural law, if it violates more basic principles of justice, then it is not a true law at all and rightly can be resisted.¹³ “Every human law has just so much of the nature of law, as it is derived from the law of nature. But if in any point it deflects from the law of nature, it is no longer a law but a perversion of law.”¹⁴

Another important category for understanding this latter idea is that of custom. A custom is any activity commonly enacted and respected by a particular community in order to teach a certain concept, particularly a moral one. In modern times, people often speak of something being “merely a custom” and so therefore less authoritative or perhaps not authoritative at all. But for classical thinkers, customs were powerful and important means by which to train people for virtue. As such, they were said to sometimes obtain the force of law. Aquinas puts it this way: “When a thing is done again and again, it seems to proceed from a deliberate judgment of reason. Accordingly, custom has the force of a law, abolishes law, and is the interpreter of law.”¹⁵ John Calvin interprets the apostle Paul in 1 Corinthians 11:14 as speaking of custom when he writes, “Does not nature itself teach?” Calvin writes, “What was at that time in common use by universal consent and custom . . . he speaks of as being natural,” and “he reckons as nature a custom that had come to be confirmed.”¹⁶ Elsewhere Calvin states, “When there is an accepted custom, and it is a good and decent one, we must accept it. And whoever tries to change it is surely the enemy of the common good.”¹⁷

One more important concept in the broader natural-law discussion is what has been called fittingness or becomingness. This concept is discussed by the Roman lawyer and philosopher Cicero in his book On Moral Duties. Cicero uses the term “becoming” to explain when something is “in accordance with nature” and presents itself in an appropriate way given the occasion.¹⁸ A simple way to describe this idea would be to say that something is proper. Something that is proper is moral, because it is based on the natural law, but it is also carried out in the right manner. It fits the occasion. The maintenance of fittingness on a social scale is sometimes called decorum. Calvin and others make use of this concept in their ethical teaching. It is important to note, however, that an idea like decorum necessarily involves a greater level of subjectivity than does the moral law itself, and so it also requires a respect for order and submission to the appropriate authorities.

Sola Scriptura

At this point in the discussion, some readers might wonder if this is a philosophy that Protestants should endorse. After all, most of the argument has relied on tradition, including non-Christian sources. Shouldn’t we instead want to adhere only to biblical law?

This sort of concern is well-meaning, but it is based on a misunderstanding. The Reformation principle of sola Scriptura does not mean that the Bible is the only authority at all. Instead, it means that the Bible is the highest authority, the authority by which all others are judged. It also means that the Bible is the only source of authority for matters absolutely necessary — that is, necessary for salvation, true worship, and righteous living.¹⁹ But sola Scriptura does not mean that no other authorities are legitimate, nor does it deny that the light of nature supplies true knowledge from God. In fact, the Westminster Confession of Faith refers to the light of nature at least five times.²⁰ In one section, the Confession states that Christian liberty does not allow for “the publishing of such opinions, or maintaining of such practices, as are contrary to the light of nature.”²¹ This is because, ultimately, the light of nature and the natural law are aspects of general revelation and therefore reflections of God’s own character.

The Scriptures themselves presuppose a certain amount of natural knowledge. After all, the Bible nowhere lays out the basic laws of logic or attempts to defend the legitimacy of causation. Indeed, the Bible proclaims that certain attributes of God can be seen “in the things that have been made” (Romans 1:20). It even says that man knows God’s righteous decree concerning the demands of justice (Romans 1:32). In short, the Bible presumes the existence of natural law and appeals to it on multiple occasions.

Natural Law in the Bible

Romans 1 is the most common source for natural law in the Scriptures. There, the apostle Paul states,

What can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. (Romans 1:19–20)

Thus, one of the lessons nature teaches is that God exists. Paul goes on to say that people knew this fact but refused to worship God or give him thanks (Romans 1:21), and so we can also say that the natural law teaches that the worship of God is a moral imperative.

Paul also speaks of “natural relations” between men and women, by which he means sexual relations. He is clear that homosexuality is unnatural since it goes against the design of creation. Romans 1:32 even says that fallen humanity “know[s] God’s righteous decree” concerning morality, as well as what we deserve if we violate it, “that those who practice such things deserve to die” (Romans 1:32). So a basic knowledge of justice, as well as the satisfaction for violating justice, is also taught by the natural law.

Philosophy with the Greeks

The New Testament also maintains that nature testifies to the difference between the Creator and the creature. In Acts 14, Barnabas and Paul say,

Men, why are you doing these things? We also are men, of like nature with you, and we bring you good news, that you should turn from these vain things to a living God, who made the heaven and the earth and the sea and all that is in them. (Acts 14:15)

Interestingly, the Greek term translated as “like nature” is actually homoiopatheis, which means more literally “like passions” or “like affections.” And so Paul claims not only that humans have a qualitatively distinct nature from God’s but also that God does not have human passions — and he assumes that his Gentile audience can learn this truth from natural law. Interestingly, when he is on Mars Hill, Paul also argues against idolatry and appeals to what his Greek audience already knows. He explains that it is wrong to think of the divine nature as “an image formed by the art and imagination of man,” since even man is prior to and above such creations (Acts 17:29). Interestingly, throughout the book of Acts, Paul argues from nature and local philosophical literature when he evangelizes Greeks, but he argues from the Old Testament when he evangelizes Jews.

Head Coverings and Submission

Paul also makes use of custom, fittingness, and decorum. We see this especially in 1 Corinthians 11:1–6, but also in 1 Timothy 2. The head covering in 1 Corinthians 11 confounds many modern readers. It clearly seems to be a cultural artifact, a custom from Paul’s time and place, and Paul even calls it a custom in 1 Corinthians 11:16 (the term sometimes translated “practice” is also translated “custom,” and this better fits the intellectual context of the passage). But just as clearly, or so it seems, Paul is commanding the custom, and he links it to nature itself. This does not make much sense if we use only modern categories, but in light of the natural-law reasoning found in earlier eras, it is perfectly intelligible and consistent. Paul’s point is that the practice of women wearing head coverings in order to speak in the assembly is consistent with the natural-law principle of submission and good order. Therefore, to preserve that good order, Paul instructs the church to retain the custom. Seeing this as an application of the natural law through the maintenance of decorum also helps us to understand how we can apply this passage faithfully today, even in a time when the specific custom has been lost in most places. We must teach the same principles, but we can find new ways to apply them to our cultural context if we follow the same concepts of propriety.²²

“Our God is a God of order, and so his creation reflects that same reality.”

We also see an emphasis on decorum in 1 Timothy 2. There, Paul is not only discussing the relationship between men and women but in fact submission to all appropriate authorities. He begins by asking for prayer for “kings and all who are in high positions” (1 Timothy 2:2a) and then moves to discuss “a peaceful and quiet life” (1 Timothy 2:2b). Everything that follows is a further discussion on the same theme. An important concern is modesty, and Paul even says that certain sorts of apparel are “proper” to this goal (1 Timothy 2:10). Again, modern readers do not immediately see how this is a sort of specialized discourse, but it comes precisely from the natural-law reasoning and rhetoric that this essay has been explaining. Paul’s goal is to promote social harmony by way of submission to one’s proper authorities. He then instructs the church about actions and customs that will help them live in such submission.

This means that what we now call “complementarianism” is a reflection of the natural law, but as one component of the larger concept of obedience to authority and peaceable order within human society. Rebellion is contrary to the natural law, as is disrespect for authority and disregard for propriety. This is because our God is a God of order (1 Corinthians 14:33), and so his creation reflects that same reality.

What Nature Can’t Teach

Nature teaches that there is a God, that he is worthy of worship, and that he has given us a basic moral order, the sum of which is equivalent to the moral content of the Ten Commandments. But there are some crucial lessons that nature cannot teach us. Ever since the fall of man into sin, natural law reveals the right way to live, and as such, it also reveals that men are not living that way. It shows that something is broken, that there is a problem. But natural law cannot explain why the order is broken. It cannot tell us what the problem is (sin) or how it came to be. For that, we need God’s special revelation, the revealed law. As Paul writes, “If it had not been for the law, I would not have known sin” (Romans 7:7). From the context, it is clear he is speaking of God’s revealed law.

“Natural law cannot explain why the order is broken. It cannot tell us what the problem is (sin) or how it came to be.”

And just as the natural law cannot explain the source of the problem, it also cannot explain the solution. “Who will deliver me from this body of death?” (Romans 7:24). The only answer is Christ, and this requires the light of the gospel, special revelation from God (Hebrews 1:2; Isaiah 49:6; Acts 13:47). And special revelation further requires a message and a proclaimer. “How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching?” (Romans 10:14). And so, while Christianity has taught the importance of nature as a teacher and a means of accountability, it has also taught the absolute necessity of grace. The only name by which men may be saved is the name of Jesus Christ (Acts 4:12), and that name must be preached by his people.

Finally, it’s important to note that the natural law does indeed teach basic compassion. The New Testament everywhere assumes that unbelievers take care of their own (Luke 6:33; 1 Timothy 5:8). Paul even states, “Perhaps for a good man one would dare even to die” (Romans 5:7). But the natural law would never direct someone to sacrifice himself for a person who didn’t deserve it. It would never teach self-sacrifice with no earthly reward in view. “But God shows his love for us in that while we were still sinners, Christ died for us” (Romans 5:8). The gospel does not contradict the natural law, but it does go above and beyond it, and in this we find our salvation.