Sometimes you see religious conservatives online argue for a moral position by simply stating that “the natural law says x.” This happened recently when Michael Knowles posted a video in which he argued, that, unlike drag shows, visiting a Hooters bar is morally legitimate because it does not “contradict the natural law.” One gets the idea that “natural law,” like appeals to “the common good,” just saves everyone the trouble of making an argument.

The discourse about it is usually so poor it makes it hard for outsiders to take it seriously. But that is not how natural law theory works. There is a great deal of disagreement and debate among advocates of natural law theory. Various standpoints carry the banner of natural law, including various theories that claim to represent natural law theory’s greatest thinker, Thomas Aquinas. But there is also something common that unites them. I would venture to say that most people embrace that common element of natural law theory whether they realize it or not. But it does not save its advocates from the work of defending their positions with arguments. And so it is with a more filled-out account of natural law, like that of Thomas Aquinas. Rather than an end to all moral arguments, such accounts provide tools to make moral arguments possible.

In perhaps its most basic sense, to invoke natural law is to affirm moral objectivity and to acknowledge a standard that transcends positive or civil law. According to Thomas Aquinas, some of natural law’s requirements are more obvious than others. Some are recognized by most societies, such as prohibitions against murder, assault, stealing, fraud, and lying—though interpretations of the specific scope and demands of these norms might differ among peoples. There is some overlap between these basic norms of natural law and what is called the law of nations, or ius gentium: the positive law common to all or most places, insofar as the rationale for such laws follows closely from these basic moral norms.

Just as some demands of natural law are more obvious than others, some may be more obvious to certain cultures than they are to others (e.g., norms against polygyny or against cousin marriage were less obvious in many cultures). In some cases, genuine moral norms may only be grasped by the wise and, it is hoped, taught by them to the rest of the community. Discussing natural law in this way will not settle many debates about its content but, again, is to affirm the existence of a moral law graspable by human reason and one which sets limits on the legitimacy of positive or civil law. Such a claim has value, and most people affirm it even if they do not speak explicitly of “natural law.” It is also a foundational presupposition of modern constitutional democracy, with its attention to abuses of sovereignty, whether from a despot or a mob, even when such abuses are consistent with current law.

Thomas Aquinas’s doctrine of natural law is at the same time a doctrine of practical reason and its principles. As such, it provides a framework for moral argument and teaching, not readymade answers to settle arguments before they start. For Aquinas, practical reason is reason applied to action—reasoning about what to do rather than what is or why. Practical reason, moreover, has its own principles—goods that we are inclined by nature to grasp in ordinary experience as we learn our native language and progress to an age of reason. These first principles of practical reason might include survival, life, health, knowledge, skillful activity, friendship, virtue, and religion. Goods like these serve as a horizon of value in which we reason about what to do here and now. Following earlier medieval thinkers, Aquinas calls the intellectual habit through which these and additional principles of practical reason are grasped “synderesis,” which other times he simply calls natural (practical) reason.

Between these most basic principles of practical reason and moral norms like those mentioned above (e.g., norms against stealing, murder, etc.) stand the common precepts of natural law, the most general normative principles grasped by natural reason—e.g., do no harm, love your neighbor as yourself, the golden rule. Some, like Thomas de Vio (Cajetan), or more recently Martin Rhonheimer, include as principles of natural reason the basic ends of the cardinal virtues—to give to each his/her own (justice), to train our passions and affections according to reason (temperance), to develop strength to overcome obstacles to the good (fortitude)—seeing the other principles, e.g., the golden rule, as more obvious implications of these. New Natural Law theorists like John Finnis have unique terminology but cover this with talk of basic requirements of practical reasonableness, which also includes what might be called maxims of prudence (e.g., the demand for commitment in projects).

Thus, according to this kind of interpretation of Thomas Aquinas, we are naturally inclined to grasp certain goods as the ends of our inclinations, along with basic moral principles that we bring to our daily reasoning about what to do. And with authentic moral experience and instruction, we can come to understand these principles and their implications for conduct further. It is easy to see how we are thus inclined to recognize certain obvious moral norms, such as those against murder, assault, etc. For instance, we recognize survival—or more abstractly, life—as a good, and we recognize that this or that person is just as deserving of this good as we are (the golden rule); we thus recognize it is wrong to take that life from them. Note that this basic moral insight is shared by all cultures.

But if there is disagreement about harder cases—euthanasia, for instance—Aquinas’s natural law theory also provides a framework for making moral arguments about them. Most of the disputes about natural law are not really about its general validity—though, for instance, opponents of moral realism deny it—but about the conclusions natural lawyers draw from it, or about what constitutes genuine moral principles. For example, the neo-scholastic “perverted faculty” argument, arguing against behavior based on the natural purpose of bodily organs, implies an especially contentious principle. But that principle is hardly embraced by all natural lawyers.

Therefore, one does natural law theory a disservice by pretending that disputed questions can be settled by simply invoking natural law. In its most general sense, natural law is an affirmation that morality is objective, as well as a claim that truths about it can be recognized and defended. If you want to persuade someone who disagrees, make an argument. Now it may be that some moral norms require additional good-faith moral experience or even practical wisdom to grasp, and thus even good arguments for a genuine moral norm may not convince everyone. But the goal of such arguments is to identify true moral norms and explain them in terms of their principles. If they are good explanations, they will at least give more credibility to the norm even if they do not convince everyone. When they do not convince, supplementary arguments might help, such as appeals to empirical research about the effects of the disputed behavior.

Finally, natural law is complementary to virtue ethics. The general norms that natural law theory allows us to identify and make explicit may rule out certain options, but they do not identify with exact precision what a reasonable course of action is in this or that context. Prudence is still necessary, and prudence requires the other virtues. At the same time, natural law theory provides an account of practical principles that are normative in the identification and pursuit of authentic virtue. Therefore, it provides general moral principles and norms that are eschewed by many contemporary accounts of virtue ethics.

There are many misconceptions about natural law theory, even by purported advocates of it. It may be unpopular in name, but it is popular in spirit, and everyone would benefit from engaging with its best proponents. Moreover, despite what some purported advocates imply online, it does not rid us of the burden of making moral arguments. In its best forms, it is a perennial doctrine that survives the many passing fads of academic moral philosophy, and it is not going anywhere. Therefore, it is in the best interest of those serious about moral philosophy to at least understand it for what it is—as a framework to begin a discussion, not a blunt instrument used to end one.