There has been a resurgence of Protestant interest in natural law in recent years, which would have seemed unlikely even a couple of decades ago. For much of the twentieth century, a broad Protestant consensus held that prominent Reformation and post-Reformation theologians opposed natural-law thinking, especially in its medieval forms. That was pure mythology. But plenty of Protestants remain uneasy and skeptical about natural law.

One chief source of unease concerns the so-called noetic effects of sin, the idea that sin has damaged not only human decision-making and conduct but our thinking as well. If this is the case, some ask, why would Christians have any expectation that natural law can play a useful role in ethics, law, or politics?

Christians do have good reason to affirm the noetic effects of sin. Scripture teaches that sin has crept into all aspects of the human person: “every intention of the thoughts of his heart was only evil continually” (Genesis 6:5). Humans have thus become “futile in their thinking” (Romans 1:21). This sobering conviction ought to temper Christian claims and expectations about natural law, but this is no reason to set the noetic effects of sin against natural law altogether. What follows is a brief case for why these two ideas are compatible and why Protestants should not set one part of their Reformation heritage against another.

Clearing Some Misconceptions

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Without doubt, some Protestant unease about natural law derives from common ideas about what natural law is—ideas that, I believe, either are misconceptions or suffer from a lack of clarity. Hence, clearing away misconceptions and clarifying some issues may be a helpful way to begin.

First, it is important to distinguish natural law from natural law theory. The former is objective while the latter is subjective. That is, natural law is the moral truth God has revealed in the created order and made accessible to human minds, while natural law theory is what human beings have thought and taught about the natural law. The reality and truth of natural law is independent of how people respond to it. For the sake of clarity, then, it’s more accurate to speak of the noetic effects of sin on natural law theory than on natural law itself. Just as Christians don’t dismiss Scripture because sinful people misinterpret it, so they shouldn’t dismiss natural law because natural law theorists make mistakes and disagree with each other.

Second, some people believe that holding a positive view of natural law means believing that moral truths are obvious to all humans and perhaps even instinctive. Were this true, there would be good reasons to dissent, since plenty of moral truths are not obvious or instinctive to many people. But Christian natural-law theorists have generally not believed that the existence of natural law entails the obviousness of moral truth. One might think of Thomas Aquinas’s discussion in Summa Theologiae I-II.94.3-4, where he acknowledges the need for “the inquiry of reason” to think and live according to natural law and distinguishes between the natural-law knowledge of “general principles” and their “proper conclusions.” The biblical book of Proverbs confirms this perspective. Proverbs does not treat wisdom (moral perception) as something obvious or instinctive, but as acquired in large part through the natural order, over time, through experience, observation, and reflection on the world. This is why Proverbs generally depicts youths as having less wisdom and elderly people more of it. The fact that natural-law truths are not obvious or instinctive to many people is no reason to reject the importance of natural law.

Third, a word of clarification about the noetic effects of sin. Even according to Protestant traditions with the gravest views of sin (such as my own Reformed tradition), fallen human beings do not get everything wrong when thinking about morality. God continues to uphold the world and human society, keeping them from utter disintegration despite their corruption. As part of this preserving grace, God keeps sinful human minds from thinking as badly as they might. To say that sin has permeated human minds is not to deny that we remain complicated creatures. Honest Christians have to admit that they get many things wrong, even with the benefit of Scripture, and that non-Christians get many things right. Scripture itself illustrates this in the remarkable story in Genesis 20, where the pagan king Abimelech (rightly!) rebuked Abraham, the man of faith, for doing to him things “that ought not to be done.”

The Prospects of Natural Law among Sinners

The preceding discussion has offered some clarifications meant to discourage a simplistic rejection of natural law because of the noetic effects of sin. But the question remains: If sin has dire noetic effects, aren’t Christians (and others who are sympathetic) fighting a losing battle when they engage the broader world using natural-law discourse? If people are sinfully prone to reject truth made known in the natural order, why not just appeal to Scripture and present moral truth as clearly and unambiguously as possible? I will respond primarily to the first question before reflecting briefly on the second.

Are Christians fighting a losing battle when they engage the broader world through natural law discourse? Part of the answer depends on how one defines victory and loss. If victory consists in the entire human community acknowledging the truth of the natural law (in the way Christians have generally understood it), then yes, it’s a losing battle. As long as this world endures, sinful people will resist the truth, and no one, Christians included, will be able to overcome this by natural law argumentation, no matter how cogent and eloquent. The kingdom of God does not come by natural law.

Nevertheless, embracing and appealing to the natural law puts a person on the right side of history. That might be a surprising claim, especially for those who have found it frustrating to engage people of different moral convictions through natural law, and who perhaps have heard that they’re on the wrong side of history for embracing natural-law morality. But it’s true. Deniers of natural law may have a temporary advantage, since it’s easier to play the skeptic and force others to make a constructive, fool-proof case for their position. But in the long run, living and arguing against the natural law is self-destructive. The case for natural-law morality proves its worth over time.

Reality Is on the Side of Natural Law

Consider this from an ontological perspective. If there is a morally meaningful natural order, then reality is on the side of natural law. Moral claims contrary to natural law may seem attractive and compelling to certain people at certain times. But because such claims run contrary to the way the world works, individuals and societies who put these views into practice will eventually get pulled back to reality.

Honoring human life, other people’s property, and truth among neighbors is not morally upright in just an abstract way. It is concretely true, in the sense that following it promotes peace and prosperity in human relationships. It provides a context in which human beings can do the sorts of things that human beings were designed and equipped to do.

By contrast, individuals and societies that despise human life, others’ property, and truth among neighbors destroy themselves. Without a context in which they can do what humans were designed and equipped to do, such people will fall into regret and despair. If they do not turn course, they will flounder, and perhaps not survive at all. It is not a coincidence that poverty and suicide rates were high in the Soviet-bloc countries, nor that rates of anxiety and mental illness have risen alarmingly among college students living amid the culture of hookups and safe spaces. To use a current buzzword, such things are unsustainable. Objective reality is on the side of natural law.

We may also consider this from an epistemological perspective. Ideas tend to work themselves out to their logical conclusions, and this also promotes the long-term advantage of natural law proponents. Moral claims contrary to the natural law are usually most compelling when they’re relatively modest and offer only a subtle threat to human goods. But over time, people push and extend such moral claims in less modest directions. If the underlying ideas that justified the initial claims are valid, then why stop there? But as people keep pushing the boundaries, the threat to human goods becomes increasingly less subtle. In the name of consistency, people feel compelled to affirm more and more radical things.

The sexual revolution over the past half century illustrates this well. It began, more or less, by challenging objections to premarital sex. It appealed to what many people found attractive anyway and it was difficult for traditionalists to explain what was so bad about it. But once that boundary was breached, toleration for homosexual relations seemed increasingly reasonable, and from there it was only a few steps to approving homosexual marriage, and from there it has proved a quick step to making gender a matter of personal choice. Few who took the first step would have found the latest step anything but bizarre, but in hindsight the progression of thought makes sense. And though most of those who have gone along with the sexual revolution to this point would forswear further steps such as legalizing polygamy, polyandry, or pedophilia, it is difficult to see what intellectual defenses will keep them at bay for long—and they already have their advocates.

By following mistaken assumptions to their logical conclusions, the sexual revolution creates a host of intellectual inconsistencies. The homosexual movement depends on an objective view of gender, but the transgender movement opposes it. The sexual revolution was supposed to be liberating for women, but it justifies things such as pornography and polygamy that have always been demeaning and oppressive to women.

If this is where opposition to natural law takes us, perhaps natural law is not on the wrong side of history after all. Because they have reality on their side, advocates of natural law have the advantage over its deniers. To appeal to the natural law is not to fight a losing battle, although it does take a broad perspective to see—and to help others see—why that’s the case.

But What’s the Use?

But why should Christians not just appeal to Scripture when engaging the world about ethics, law, or politics? To conclude, I mention two considerations briefly.

First, since Scripture itself affirms that the created order reveals God’s moral law and that all people are accountable to God for their response to it, it is self-defeating for Christians to turn their backs on natural law for the sake of promoting biblical teaching. Scripture should be a source of confidence that creation is morally meaningful and that objective reality is on Christians’ side.

Second, appealing only to Scripture in public discourse sends a bad message, one that’s also self-defeating because contrary to Scripture itself. The bad message is that matters of great moral importance—whether protection of all human life, the good of marriage and family, or the like—are simply Christian things. On the contrary, such matters are human things. Their moral truth rests ultimately not in biblical commands but in how God created human beings in his image. In matters of basic morality, Scripture commanded what it did, not to make certain responsibilities obligatory, but because they were already obligatory for human persons.

We should not want people in the public square to think that respect for all human life, property, or the family is just a quirk of those who believe the Bible. Whether or not we use the term explicitly, by appealing to natural law we send the message that these are truths that every human being can know—and truths that we all have a duty to uphold.