In a recent essay at Law and Liberty, F. H. Buckley sought to rehabilitate the old charge that natural law and natural lawyers commit the so-called naturalistic fallacy by violating Hume’s dictum that it is impossible to derive an ought from an is. As I see it, Hume’s is/ought dichotomy is driven by his radical epistemic skepticism of everything of consequence: God, the soul, the self, other minds, an external world, and any oughtness that is more than what he designates (seemingly by fiat) as a moral sentiment. Moreover, his metaphysics—in particular, his rejection of final causality as part of the nature of things—constitutes a necessary condition of the is/ought dichotomy, as Alasdair MacIntyre shows in After Virtue (pp. 57-59 and 148). MacIntyre rightly holds that an ought can be inferred from an is in a metaphysic in which the function of something is part of its nature, part of what it is—for in that case the is does not refer to brute facts devoid of oughtness; oughtness is built into the nature of things (see also my argument here, Anthony Lisska pp. 195-201 here, and Edward Feser pp. 138-40 here).

But there is another, perhaps much stronger and more important objection to the misguided allegation that natural lawyers commit the naturalistic fallacy. No natural lawyer in the classical natural law tradition derives an ought from an is (or from facts devoid of oughtness), because, when it comes to practical (or moral) reason, natural lawyers do not derive ought at all—at least not the most fundamental oughts. Rather, when it comes to moral reason—and especially the apprehension of our most fundamental obligations—they begin with ought. Put another way, in an important sense ought is underived. Or, if you will, it’s stipulated in the major premise. This can be seen by considering the order of natural law precepts as conceived by Thomas Aquinas in that part of the Summa Theologiae often denominated the Treatise on Law (ST I-II, Question 90-108).

First Principles of Reason

Like Aristotle, Aquinas distinguishes between theoretical and practical reason. In all reasoning, according to Aristotle and Aquinas, there are first principles of reason that do not admit of demonstration. They are beginning points of reasoning and, as first principles, are indemonstrable. Consider geometry. In geometry, theorems are proved by way of axioms. But axioms cannot themselves be proved. They’re axiomatic. For theoretical reasoning more generally, the law of non-contradiction constitutes a first principle, as does the law of identity (a thing is identical with itself or A=A). While the law of non-contradiction cannot coherently be denied (its denial presupposes its universal validity, making the denial self-defeating), it also cannot be argued for without begging the question. Yet, as Aristotle and Aquinas hold, all theoretical demonstrations assume its universal validity. The fact that the law of non-contradiction cannot be proven does not count against it. The same goes for geometric axioms, since they are the first principles of reasoning.

For classical natural lawyers like Aquinas, something analogous is true of practical or moral reason (what Aristotle calls phronesis). According to Aquinas there is an order to the precepts of natural law. There are universal first principles, or primary precepts, and then there are secondary precepts that derive from the primary ones. Secondary precepts include immediate implications from first principles that, like the first principles, hold for all people, at all times, and in all places—without exception—and more remote implications that hold for the most part but admit of exceptions.

For our purposes, what matters is that while the secondary precepts of the natural law are derived, primary precepts are not. Rather, primary precepts are first principles and as such are indemonstrable. They are the beginning of moral reasoning and, like geometric axioms, the basis of moral demonstration. They are not theorems or conclusions. We begin with them without arriving at them by a chain of reasoning. This shows how Hume and others misconceive natural law, and shows why the naturalistic fallacy, though misconceived, is also beside the point. Humean critics of natural law presume natural lawyers like Aquinas derive every ought. But since the most fundamental oughts are first principles, they are—in the order of moral reasoning—underived (something argued both by Aquinas and C.S. Lewis, among others).

The Good and Human Nature

According to Aquinas, the principle of morality that serves the role in the realm of practical reason that the law of non-contradiction serves in theoretical reason is this: Good is to be done, and evil avoided. As a first principle of practical reason, this precept is not derived from anything else. When it comes to moral reasoning, this is a beginning point. In a misbegotten argument in his Ethics Without God, Kai Nielsen dismisses Aquinas’s first principle as purely formal and tautological. But this is quite obviously not so—as is apparent to anyone who has read Anthony Lisska, Ralph McInerny, J. Budziszewski, or Edward Feser on Aquinas and the good (see also Chapters 4 and 5 of my Uncovering the Constitution’s Moral Design).

In classical philosophy the good of anything has the nature of an end. The good of a thing is the fulfillment or performance of its proper function; its highest good is therefore the performance of its proper function with excellence. We must understand the nature of things and their good in terms of final cause (purpose, aim, or goal). The good of the heart consists in circulating blood through the body and thereby providing life to it. Any paramedic seeking to save the life of someone who is non-responsive understands this just as much as a heart surgeon.

Aquinas understands human nature as complex. Human beings are substantial, animate, and rational (ST I-II, Q. 94, a. 2). And there are goods perfective of each part of human nature. For instance, the good of any substance is existence. From this Aquinas infers that human beings have an obligation to preserve the good of human life. But he does not infer this obligation from an oughtless is. Rather, the obligation to preserve human life flows from the indemonstrable and underived primary precept that good is to be done and evil avoided and the fact that the conservation of life is good for humans as existing things.

The same goes for the animal nature of human beings. The good perfective of our animal nature (given the sort of animals we are) includes having and educating our young. The obligations in question, however, derive from animal nature—and what perfects it—together with the primary precept that good is to be done and evil avoided. So also with the rational element of human nature. Because human beings are rational, Aquinas holds they have obligations with respect to knowing the truth about God and living in society as well as avoiding both ignorance and incivility toward those with whom one must live in community. But, again, the obligation does not come simply from the fact that knowing the truth about God, shunning ignorance, and living in society are the proper functions or goods of human rationality (though they are). Rather, it comes from the fact that these are good for human beings as rational together with the primary, first principle that good is to be done and evil avoided.

The foregoing account of moral reason applies to obligations to refrain from actions like murder, theft, and adultery as well. These acts obstruct human well-being and are contrary to the proper function of human nature. But the obligation to refrain from them follows from the precept that good is to be done and evil avoided together with the reality that these are evils that distort and corrupt human nature. Here too there is no move to ought from some oughtless fact or is. There is no derivation of a value from some valueless fact.

Ought and Is

No natural lawyer has ever proposed inferring oughts from oughtless facts. Taking the locus classicus of natural law, Thomas Aquinas, as our point of departure, we discover something true of every major thinker in the classical natural law tradition. Natural lawyers of varying backgrounds begin moral reasoning from indemonstrable first principles of practical or moral reason that prescribe and therefore stipulate an ought right at the outset—namely, that good is to be done and evil avoided.

If one reads philosophical, theological, and political-theorist natural lawyers, one never encounters a proponent of natural law deriving an ought from an oughtless is just because they begin any moral demonstration with the first principle of natural law, where the first principle is a prescription, i.e., an ought. That natural lawyers begin here should be unsurprising. As Lewis writes in The Abolition of Man regarding the first principles of practical and moral reason:

Unless you accept these without question as being to the world of action what axioms are to the world of theory, you can have no practical principles whatever. You cannot reach them as conclusions: they are premises. You may, since they can give no “reason” for themselves . . . regard them as sentiments: but then you must give up contrasting “real” or “rational” value with sentimental value. All value will be sentimental; and you must confess (on pain of abandoning every value) that all sentiment is not “merely subjective.” You may, on the other hand, regard them as rational—nay as rationality itself—as things so obviously reasonable that they neither demand nor admit proof. But then you must allow that Reason can be practical, that an ought must not be dismissed because it cannot produce some is as its credential. If nothing is self-evident, nothing can be proved. Similarly, if nothing is obligatory for its own sake, nothing is obligatory at all (40).

Aquinas and Lewis and natural lawyers more generally begin with prescription. Moral reason starts with an ought in the premises whose apprehension is immediate and prior to a process of reasoning.

Variation in Natural Law

Once the red herring criticisms of natural law derived from Hume and advanced by folks like Nielsen and Buckley have been dismissed, I can imagine only one perhaps initially plausible objection that remains. If according to natural law there are first principles of morality that are part and parcel of reason itself, how come there is so much variation in morals, customs, and laws across cultures? Ancient sophists raised this objection to the idea of natural right, which Socrates, Plato, and Aristotle in turn defended (see my treatment of the ancient argument over natural right here).

If according to natural law there are first principles of morality that are part and parcel of reason itself, how come there is so much variation in morals, customs, and laws across cultures?

We should begin by noting that the move from cultural relativism (even with regard to moral convictions) to moral relativism is a non sequitur. It may be that there are things right for all but that opinions about these nevertheless vary considerably. We could ascribe the variance to many things including the noetic effects of sin and the Fall. Natural law holds that some things are right for all people, at all times, and in all places. Varying convictions about what these are is neither here nor there as to whether some things are in fact right always, everywhere, and for everyone.

Still, Thomas Aquinas held that some things are the same in all both as to rectitude and knowledge—or as J. Budziszewski likes to put it, some things are both right for all and known to all. Aquinas did not, of course, mean that this knowledge was conscious or formulated. So far as his claim is concerned, the knowledge in question may be latent and inchoate—built into or impressed upon the very frame of human reason. And it may be the sort of knowledge by means of which, for instance, we know the wrongness of murder without knowing that we know (classical natural law does not presuppose the sort of internalist epistemology that we find in Descartes or Locke).

What about this claim of radical cultural variation in moral knowledge across time and place? Well, the claim is empirical. And, as it happens, the claim is also empirically false. There is of course real and important variation across time and place (as any reader of Herodotus knows). Nevertheless, as C.S. Lewis writes in “The Poison of Subjectivism”:

[W]hat of the . . . modern objection—that the ethical standards of different cultures differ so widely that there is no good common tradition at all? The answer is that this is a lie—a good, solid, resounding lie. If a man will go into a library and spend a few days with the Encyclopedia of Religion and Ethics he will soon discover the massive unanimity of the practical reason in man. From the Babylonian Hymn to Samos, from the Laws of Manu, the Book of the Dead, the Analects, the Stoics, the Platonists, from the Australian aborigines . . . he will collect the same triumphantly monotonous denunciations of oppression, murder, treachery, and falsehood, the same injunctions of kindness to the aged, the young, and the weak, of almsgiving and impartiality and honesty. He may be a little surprised (I certainly was) to find that precepts of mercy are more frequent than precepts of justice; but he will no longer doubt that there is such a thing as the Law of Nature. There are, of course, differences. There are even but the blindnesses in particular cultures…But the pretence that we are presented with a mere chaos—though no outline of universally accepted value shows through—is simply false and should be contradicted in season and out of season wherever it is met. Far from finding a chaos, we find exactly what we should expect if good is indeed something objective and reason the organ whereby it is apprehended—that is, a substantial agreement with considerable local differences of emphasis and, perhaps, no one code that includes everything.

While there are significant differences across culture, other scholars provide evidence that supports Lewis’s conclusion. Thus, in “The Relations Between Religion and Morality in Primitive Culture” in the journal Primitive Man, John M. Cooper famously wrote the following:

The peoples of the world, however much they differ as to the details of morality, hold universally, or with practical universality, to at least the following basic precepts. Respect the Supreme Being or the benevolent being who takes his place. Do not “blaspheme.” Care for your children. Malicious murder or maiming, stealing, deliberate slander or “black” lying, when committed against friend or unoffending fellow clansman or tribesman, are reprehensible. Adultery proper is wrong, even though there be exceptional circumstances that permit or enjoin it and even though sexual relations among the unmarried may be viewed leniently. Incest is a heinous offense. This universal moral code agrees rather closely with our own Decalogue understood in a strictly literal sense. It inculcates worship of and reverence to the Supreme Being or to other superhuman beings. It protects the fundamental rights of life, limb, family, property and good name.

In a similar vein, ancient Greeks like Socrates in Xenophon’s Memorabilia or Aristotle in his Rhetoric spoke of the unwritten, common laws of right and wrong that have their foundation in nature. Cooper and Lewis, among others, supply evidence that supports their claim (see this piece by Richard H. Beis).

For natural lawyers, the fundamental requirements of the moral law are inscribed on the human heart and attested by conscience, even if our fractured condition obscures them to some degree.

This claim that the unwritten, common laws of right and wrong are founded in the nature of things does not mean that right and wrong are inferred from what always or usually happens. The claim is not statistical. The claim is not that the natural law is usually obeyed or that we can infer its requirements simply by observing human behavior. Nor is there an inference as to what counts as right or wrong from the brute facts of a morally indifferent human nature. Rather, for natural lawyers, the fundamental requirements of the moral law are inscribed on the human heart and attested by conscience, even if our fractured condition obscures them to some degree. In Christian terms, the Creator has not left Himself without a witness. When it comes to moral reasoning, natural lawyers start from there.