Natural Law without Nature? Aquinas to the Rescue

Natural law has had a hard time in the modern world. Jeremy Bentham (1748-1832) castigated the natural law theorists of his day for promoting “personal opinions and sentiments” as standards of right and wrong. He offered utilitarianism as a replacement, versions of which have taken the lead in modern university courses on ethical theory. Immanuel Kant (1724-1804), dissatisfied with utilitarianism and committed to a “Copernican revolution” in ethics and metaphysics, developed a subjective replacement for natural law: “Act only on that maxim whereby thou canst at the same time will that it should become a universal law.” Kant surmised that if we simply sat down and considered whether we would want everyone to do what we were planning to do, without self-contradiction, we would have sure-fire guidelines for right and wrong.

This is called the “universalization hypothesis.” Kant’s successors were unconvinced. G. W. F. Hegel (1770-1831), for example, argued that with the Kantian method one could justify either communism or a system of private property without any self-contradiction. More recently, Henry Veatch shows how a hypothetical Nazi, trying to “universalize” his maxim, “I should eliminate all Jews,” could justify it by carefully rephrasing the moral “test.”

Opposition to natural law theory continues in our own time. The magazine First Things, dedicated to defending “first principles, for the right ordering of public life,” published Paul Griffiths’s “The Nature of Desire,” which attacked natural law on the basis of the infinite number of unrealizable desires, as evidenced in the plays of Shakespeare and other literature. J. Budziszewski wrote “Natural Law, Revisited,” in the same magazine and, aside from a brief reference to a natural law governing reproduction, was silent about any particular version or theory. Even Hadley Arkes, whose book First Things initially inspired the creation of the magazine by that name, devotes only a single chapter in his most recent book, Constitutional Illusions and Anchoring Truths: the Touchstone of the Natural Law, to natural law, in which he disclaims any interest in any “theory” of natural law and gravitates toward Kant’s “universalizability” approach.

Arkes puts forward a brilliant analysis of the application of legal doctrines like ex post facto and “prior restraint” and brings out blatant infractions of the law of non-contradiction in specific cases like Lochner, which is considered a famous landmark by legal scholars like himself, and the “Pentagon Papers,” published during the Nixon administration. But such important constitutional insights are not traditional natural law as espoused by Cicero, Aquinas, the late-medieval Catholic scholastics, and even later Protestant spokesmen like Grotius, Cumberland, and Pufendorf.


Much of the contemporary disinterest in traditional natural law can be traced to David Hume (1711-1776) who, in his ethical work, warned against “deriving an ‘ought’ from an ‘is'” — in other words, basing moral rules on factual states of affairs. My 2004 book, Natural Law: An Introduction and Reexamination, argues that Hume has been widely misunderstood. And Hume himself, in the moral theory he ended up with, derives the fundamental “oughts” of human nature from inclinations and sentiments, which certainly qualify as an “is.” Rev. Frederick Copleston, S.J., famous for his nine-volume History of Philosophy, suggests that Hume himself should be categorized as a “natural law” philosopher.

But contemporary ethicists, fearing ridicule for even the appearance of deriving theories from something existing (and gradually emerging by biological evolution) like “human nature,” tend to look to “rationality” itself, in various guises, as the source of morality. Thus “new natural law” theorists, like John Finnis and Germain Grisez, noted for their stalwart defense of Pope Paul VI during the firestorm of rejection that followed his encyclical on contraception, propose a theory “without metaphysics” depending on certain “self-evident” basic human values, including knowledge, life, play, aesthetic experience, sociability (friendship), practical reasonableness, religion, and the pursuit of ultimate questions.

But I began to suspect the alleged “self-evidence” of these values when I read the long and intricate proof in Finnis’s Natural Law and Natural Rights that the value of knowledge is self-evident. The self-evidence he has in mind is certainly not the intuitive kind. I and other philosophers have concluded that this “new natural law” theory is interesting and perhaps valid, but it is not a natural law theory based on the givens of human nature.

Thomas Aquinas, who lived before the Humean restrictions about “is” and “ought,” dared to go beyond the abstract principle, “Do good and avoid evil,” to point out three specific “oughts” derived from the tendencies and appetites of human nature itself. (This triad of precepts is not original with Aquinas, but appears in Cicero, the Roman jurists, Aquinas’s scholastic predecessors and successors, and even as late as the 18th century in Montesquieu.)

The most important precept is indeed, as contemporary ethicists often maintain, to act rationally. But for Aquinas, rationality is not just about avoiding self-contradiction; he points out two specific and necessary manifestations of rationality: 1) in the theoretical realm, always pursue the truth; and 2) in the practical realm, contribute to communal and societal harmony. A second precept, experienced by humans as well as animals, is to procreate and care for offspring; humans, of course, require an extraordinarily long period of nurturing. And the third precept is what is called in common parlance the “law of self-preservation.”

These natural laws are also rights. The duty of seeking the truth implies the right to the truth, and certainly involves a right to necessary information and education; the duty of contributing to communal harmony implies the right to work towards that end — a right with political implications; the duty of caring for one’s offspring (Aquinas would consider this the main argument against abortion, not the general “right to life”) implies the right to reproduce (not the bizarre modern inversion of “reproductive rights”); and the duty of self-preservation implies the right of self-preservation (implying the right to the wherewithal necessary for maintaining physical life).


Although Protestant as well as Catholic philosophers have argued for natural law, some Protestants, for example Karl Barth, have found it inimical to the primacy of the Christian gospel. And the reaction against traditional natural-law theory continues among Protestants. A forthcoming Lutheran anthology on natural law boasts that it is not concerned with the wrong (Thomistic) version of natural law: “No contemporary thinker is interested in a wooden repristination of the natural law that is tied necessarily to the particular metaphysical foundations in the Thomistic-Aristotelian synthesis.”

The Thomistic theory of natural law has three important advantages over its avatars: 1) it is based legitimately on the realities of human nature, on the basic impulses that all humans share; 2) it is intuitively connected with natural rights, as “the other side of the coin”; and 3) it offers specific guidelines about moral behavior, whereas general guidelines about “universalization” or conforming to “basic values” do not.

By default, the Thomistic “metaphysical” natural law has been connected historically with Catholic tradition. In this tradition, natural law has been considered a bridge toward ethical and legal unanimity with non-Catholics and even non-Christians, on the supposition that the theory defends the basic moral presuppositions for all humans.

Optimally, however, Christianity will not be satisfied with mere adherence to natural law, but will impel believers to go even beyond the basic tenets — going “the extra mile” (Mt 5:41), offering your coat to someone who takes your tunic (Lk 6:29), lending to would-be borrowers and forgiving debts (Mt 5:42, 6:12), possibly even “turning the other cheek” when assailed by adversaries (Mt 5:29; Lk 6:29). Such responses, of course, leave natural law far behind.

Howard Kainz


Howard Kainz is professor emeritus at Marquette University. He is the author of several books, including Natural Law: an Introduction and Reexamination (2004), The Philosophy of Human Nature (2008), and The Existence of God and the Faith-Instinct (2010).

  • Donna

    depends on seeing things as having true natures. To the modern world, nature is Play-doh, to be shaped as we see fit. An example: Arizona gets too hot in the summer to be comfortable. The natural solution would be to leave Arizona during the summer. The real world solution : crank up the AC.
    I think of that saying of Pavel Chichikov Mark Shea quotes a lot : the world going from “What can it hurt ? ” to “How were we supposed to know ?” The thing is, the usual response to the latter isn’t, “Let’s stop doing it”. It’s either “Well, we can live with the consequences” or “We’ll keep doing it, and improve our technique to lessen the side effects. ”

  • Nick

    All the alternatives to the Divine and Natural Moral Law appear to just simply be variants of the Golden Rule. Fortunately for us Christians, the Golden Rule is Christian doctrine. So we got both the Natural Law and the Golden Rule, and I think that’s a pretty awesome package of morality.

  • HKainz

    To Nick: The Golden Rule is not just “Christian doctrine.” As I mention in my 1988 book, Ethics in Context, it is found in Judaism, Confucianism, Hinduism and Buddhism.

  • Mena

    We’re living in an age where postmodern experimental liberal society is hell-bent on implementing crazy ideas (via laws and public policy) and escalating commitment no matter the horrific results. The end game of that process is tyranny/despotism: the masses will be enslaved, and the government rulers will be the deciders, as it is in many immoral despotic regimes around the world at present.

    The only solution to this is to create heavily Christianized territories and states in the U.S.A. that legislate the correct ideas and enforce them. Moral anarchy and “progressives” must be constantly expelled and rejected. In this scenario, the Christianized territories and states will thrive and succeed while the pagan ones will implode under the weight of their own folly.

    This is where we are today. Any other solution will result in enslavement to dictatorship with ensuing persecutions. The left have become fascists.

  • Gordon

    The Golden Rule is only found in the positive form in the teaching of Christ. That is much more demanding morally than the negative version taught by others. Indeed the negative version might be seen as an expression of the law. In contrast, the positive version reflects the fulfillment of the law, the introduction of a deeper level of moral consciousness and a law written on the heart. This is made possible by the New Covenant and expressed in the Sermon on the Mount. It is summarised as love God and love your neighbour and starts with an act of faith in the One who has authority to determine good from evil. Thus do not murder becomes do not hate and do not commit adultery becomes do not lust. The negative version is an ethical code of law. The positive version is empowed relationships. God becomes the standard by which we should live – “Be Holy because I am Holy” Lev 11:44 and 1 Pet 1:15-16. It is only in the dynamic power of the Holy Spirit that this is possible. It is an ethic based on relationship with God which in turn impacts relationships with our neighbours. That is not achievable without active empowering by God (Christ living in us) and that is why the Golden Rule loses its meaning if it is reduced to a vague syncretist moral code or an unattainable ideal which we fruitlessly strive to fulfill in our own human wisdom and strength.

  • HKainz

    To Gordon: If the Golden Rule is understood as concerning human rights, the negative and positive versions become equivalent. For example, in Judaism, “What is hateful to you, do not do to your neighbor,” is saying that if you consider you have certain natural rights, you should grant those rights also to your neighbor.

  • Carlos

    Donna, it is worse than that. Play-Doh has a nature. Modern society denies the objective truth of anything and everything, remaining only subjective perception. This is why AC is peceived as the solution to a problem, even if it will blow even hotter air towards the neighbor, demanding his AC to be cranked up, and so on: as long as one is cooler, the heat *does not exist*. Likewise, human nature is perceived to be a construction: people build their “natures” by the way they dress, the appearance they choose to have (tattoos, piercings, etc.).
    It is a perverted form of a Kantian metaphysics, in fact. The only difference is that it does not allow for a universality of Reason, for which feelings substitute. That is why nowadays the same people who cannot believe in natural law support contradictory notions of 3rd-generation rights.

  • Michael PS

    Those, like John Finnis, who try to

  • AT

    So my question is this: when will the Church start applying concepts of natural law, including the Golden Rule, in her own affairs? It is possible that this not the case because utilitarian, might is right, concepts by modernists like Escriva prevail, rather than Aquinas? For example the view that the only path to