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Until quite recently, natural law thinking had been a Catholic preserve. My interest in it was awakened during my days as a Jewish undergraduate at the University of Chicago, by the great Leo Strauss—himself a serious, though nonobservant, Jew. When I told Strauss of my interest in natural law, he told me, “I am not a natural law thinker,” and suggested I study with Yves Simon, a devout Catholic. Later, as a graduate student in philosophy, having received my rabbinical ordination, I went to Georgetown University to study under the Catholic natural law theorist Heinrich Albert Rommen.

It is understandable that many Catholics have been active in natural law discourse and advocacy, for one might say that natural law theory is the Catholic tradition’s most consistent exercise of practical reason. Of course, Catholics must admit that non-Catholics like me may also be natural law philosophers, because natural law presents itself as philosophy, and philosophy necessarily claims to be universal. In fact, most Catholic philosophers have welcomed non-Catholics like me into the natural law enterprise, in which they don’t wish to be alone. Because of this welcome from the earlier shareholders, modern natural law is a truly interreligious enterprise. It includes Jews, Protestants, and, most recently, Muslims.

But if natural law discourse and advocacy are pursued only by members of the three “Abrahamic” religions—Judaism, Christianity, and Islam—the question arises: Must one be religious in order to be a natural law advocate? The fact that natural law is an interreligious or interfaith enterprise does not necessarily imply its universal rationality. Indeed, isn’t it likely that advocacy of natural law arises from theological reasons, and is thus limited by them? Just as the Catholic magisterium could be seen as teaching a universally applicable morality, prescribed by its own revelation-based authority, so too the Jewish tradition’s teaching of a universally applicable morality could be seen as issuing from its revelation-based authority. In this view, then, natural law is universal only in its application; in its conception, it remains particularistic. What is universally binding is represented to the world as stemming from God’s particularly authoritative will rather than from his universally persuasive wisdom.

Let me cite an example of a more general Jewish view of the moral law that binds Gentiles as well as Jews. One of the greatest medieval commentators on the Talmud was the late-thirteenth-century Provençal theologian Rabbi Menachem ha-Meiri. He had to address the rather problematic Talmudic ruling that, were a society to be governed according to traditional Jewish law (halakhah), Gentiles would not have the right to be compensated for damages to their property, at least in certain circumstances. Several earlier theologians had tried to explain this seeming double standard as a penalty that the rabbis enacted because the Gentiles did not respect the property rights of others, especially Jews. These Gentiles were thus considered outlaws, like pirates who had been judged “enemies of humankind.” The rabbis had penalized these ancient Gentiles by denying them the right of due process of law. The law thus defends the property rights only of those who respect the property rights of others. But did the rabbis mean to penalize all Gentiles, or only the Gentiles in Roman Palestine, who were seen as agents of Roman persecution of the Jews?

Whereas his predecessors had offered an ethical and legal interpretation of the Talmudic ruling, Meiri offered an ethical and theological one. For Meiri, the immorality of these ancient Gentiles arose from their being idolaters who did not accept any law revealed by God. He makes this distinction in order to differentiate ancient Gentile idolaters from the Christians and Muslims of his own time. In Meiri’s view, Christians and Muslims differed from the ancient Gentile idolaters in that “they are bound (megudarot) by Law.” But what kind of “law” does Meiri mean? The Hebrew (originally Persian) word Meiri uses is dat—the same word that in modern Hebrew denotes “religion.” Indeed, for most thoughtful people in the Middle Ages, law and religion were two sides of the same coin. Law can make its demands because it is religious: It is revealed by God. God’s revelation is normative ipso facto. In this view, the religion that makes law authoritative is a revealed religion. It is the religion of the God who commands humans in the context of their own particular sacred histories.

Furthermore, in Meiri’s understanding of dat (“religious law” or “lawful religion”), the revealed law systems of Judaism, Christianity, and Islam all have an essential theological point in common, one that makes possible an interreligious recognition of a common morality. Each religion’s law claims to be the revelation of the same God, who is the Creator of heaven and earth. This is the same God who created law itself, by which God justly governs the human creatures created in his image. This would explain why the basic moral norms taught by Judaism, Christianity, and Islam are so similar: They come from the same God, the one and only Creator-God. Moreover, the lawful commonality Jews and Christians share is not only that we all obey the same divine Creator, Lawgiver, and Judge, but that we base our moral norms on the same particular revelation: the Hebrew Scriptures, or “Old Testament.” The result is what some have called the “Judeo-Christian ethic.” Yet in this interreligious view, Jews cannot and ought not tell non-Jews what Jewish law requires of them universally as human persons. Instead, Jews can only tell Christians and Muslims: “This is what your own revealed law commands you to do, which is the same as what our revealed law commands us to do.” Christians and Muslims can speak similarly when talking to one another, and when talking to Jews. Here, we have what is called an “overlapping consensus.”

Meiri’s interreligious approach to moral law represents a move toward a more general, inclusive view of moral law. It enables me as a Jewish thinker to engage both Christians and Muslims on moral issues with theological integrity. The type of interreligious dialogue I have been able to conduct would be religiously impossible without the theological achievement of Rabbi Menachem ha-Meiri and those who followed him.

With his mastery of the rabbinic sources, Meiri also argued against Jews who insisted that Judaism had a monopoly on truth and righteousness. Triumphalists always insist, down to our own time, that despite similarities in doctrine or praxis, Judaism shares nothing of substance with either Christianity or Islam. No doubt we can find triumphalists among Christians and Muslims, too. We Jews, Christians, and Muslims all perennially face such opposition to an interreligious approach to moral law.

However theologically valuable Meiri’s inclusive approach remains for us, it is not universalistic enough, at least not for philosophers; and we have to accept that the only way our natural law arguments can be heard in the public discourse of an essentially secular society is by being universal arguments in principle. These are arguments that can be made to any or all rational humans, and that must be more inclusive even than Meiri’s premodern “multi-culturalism.” Such arguments can only be made philosophically.

Though Meiri’s interreligious view of morality is impressive theology, another, more philosophical Jewish view sees a universal morality operating in the world ab initio, before uniquely Jewish revelation occurred. More than a century before Meiri, Maimonides went beyond the interreligious or “interhistorical” view of the origin of law by stressing that the inception of law takes place at the same time as the creation of humankind. The creation of an intelligible cosmic order by Divine Wisdom is pre-historic. Thus, law’s inception is likewise prior to history. Law is not produced by any people’s special historical revelation. It is “natural”—a truly ­universal creation.

The creation of natural lawfulness or morality (ius naturale) coterminous with the creation of human nature means that our existence is essentially lawful or moral. Natural law is knowable by humans because of the essential lawfulness of our created nature. Of course, we humans may act morally or immorally. We may uphold or transgress what is considered by ourselves or others to be the moral law. Often, when we transgress what others consider the moral law, we justify ourselves by calling that law “heteronomous,” an alien and imposed law, which we have not accepted. To say so implies, though, the existence of some moral law that we do accept. When we transgress the moral law we do accept, we cannot escape being accused of wrongdoing, even if the only accuser is our own conscience. We cannot be amoral. We cannot be without a moral law, however inchoate the law may be.

The task of human reason, therefore, is to distinguish between what is moral and to be done and what is immoral and not to be done. It is in our nature: We cannot evade distinguishing between right and wrong, justice and injustice. Plato pointed out that even a would-be tyrant has to convince those he would have obey him that the exercise of his might is just. Political authority requires moral justification in order to be acceptable to all free, rational human persons (a point made most famously by Kant).

This view of natural law is more philosophically attractive than the interreligious view examined above, for it sees a moral law that is universally evident to and valid for all humans. This law is ­naturally evident and valid because it is in accordance with the rational, normative nature of humankind. Kant called this view the “metaphysic of morals”; the German Jewish Neo-Kantian philosopher ­Hermann Cohen called it “the theory of praxis.” This view explains why natural law claims the obedience even of those humans outside the three Abrahamic religions. It explains why natural law demands the obedience even of those who have no religion at all.

Religious thinkers can argue more persuasively in the larger world by employing a philosophical conception of natural law than by employing the interreligious conception of common moral law. As philosophers dealing with human nature per se (the subject of natural law), they can enter public reasoning in a secular society with integrity. By a “secular society” I mean a society that does not take its legitimizing warrant from any particular historical revelation. In a secular society like the United States, the legitimizing warrant is not theological but philosophical, as when Thomas Jefferson declared American independence by invoking self-evident truths. Yet, for Jefferson, these self-evident truths concerned the rights with which all humans had been “endowed by their Creator.” Jefferson’s secularity, then, was not atheistic, but rather theistic or “Unitarian” in the ­early modern sense. Still, Jefferson was not arguing as a Christian (nor as a Jew), insofar as his argument was not based on revelation.

The acceptance of the divine source of natural law is not, then, philosophically necessary. But the acceptance of revealed law’s need for natural law is ­theologically necessary. The acceptance of natural law is what makes it possible for any human community to accept the higher, revealed law of God. The acceptance of the lower natural law (lex naturalis) makes the acceptance of the higher revealed law (lex divina) more than an irrational “leap of faith.” The acceptance of the higher law in history presupposes the prehistoric acceptance of the lower law, which is the retroactive acceptance of created, normative human nature. This relation between revealed and natural law provides the theological warrant for religious natural law thinkers to practice natural law as intellectual discourse and political advocacy. In this sense, this essay’s titular question—“Does Natural Law Need Theology?”—should be answered, “Yes.” Nevertheless, as we shall see, natural law does not need theology in the way a logical conclusion needs its premise. The connection is not that simple.

The ancient rabbis taught that any people who had not accepted basic natural law precepts (such as the unequivocal prohibition of murder) would be unable to accept the higher, more singular law of God revealed to Moses and the people of Israel at Mount Sinai. That is why the Edomites, the descendants and willing followers of blood-shedding Esau, rejected the higher law when it was offered to them by God. Those not living justly or correctly with their neighbors are in no position to live justly or correctly with God—for God’s covenantal relationship is with a human community, rather than with lone individuals. Humans living in an irrational, inhumane society are incapable of living with God in a covenantal relationship, inasmuch as they have no true community in which that relationship could be lived. Natural law is not revealed law’s product; it is revealed law’s precondition. That precondition is subjective insofar as it enables humans to accept rather than ignore God’s higher law. It is objective insofar as it enables humans to suppose the world is not impermeable to revelation.

Thomas Aquinas well expressed this precondition when he said: “Grace [or revelation] does not abolish nature (non tollit naturam), but perfects it.” Without the acceptance of human nature’s inherent and lawful limitations, without which a true human community could not function, revelation from heaven would have no place to land on earth. Aquinas’s insistence on the interrelation of revelation and nature resonates in Jewish theology no less than in Christian theology. Of course, Jews, Christians, and Muslims differ theologically as to what exactly constitutes “­perfecting grace.”

As for the question, “Must one be religious in order to be a natural law thinker?” the short answer is, “No.” But it certainly helps.

Religious commitment is helpful to the natural law thinker, in that universal natural law morality is a necessary though not sufficient condition for human flourishing. A commitment to natural law satisfies one essential aspect of human nature: what Aristotle called “human political being,” which is manifest in our need to live and discourse rationally with other humans in peaceful justice. It does not satisfy the other essential aspect of human nature: our nature as what the Bible calls “the image of God.” That term seems to denote our need and capacity to be in direct relationship with God, a relationship the Bible calls “the covenant” (ha-berit). Only our revelation-based theologies can constitute the domain that obtains, as the rabbis taught, “between man and God.” Yet this religious domain constantly intersects with the political domain that obtains “between humans themselves.”

The human domain is dealt with philosophically in natural law thinking and political advocacy, whereas the divine-human domain is dealt with theologically in our religious traditions. There is nothing in the human realm that does not have some theological implication; and there is nothing in the divine-human realm that does not have some philosophical implication. For example, God holds Cain responsible for violating the prohibition of murder. Cain is responsible for the murder of Abel because he should have recognized the rationality of its prohibition—even though the norm will not become direct revelation until the commandment given at Sinai: “You shall not murder” (Exod. 20:13). Murder is wrong because it is an irreparable assault on a fellow human—and, worse, an irreparable assault on God, performed on the body of a human who is the image of God.

The affirmation of human inviolability is enhanced by our theological doctrine that all humans are created in the image of God, that all humans are capable of a life with God, and that all humans can be redeemed from death by God. All humans are especially beloved of the God who has created us so uniquely to be like himself. Being the image of God, each human has the right to be loved by all other humans; and acting as the image of God, each human has the duty to love all other humans. To exercise that right and duty maximally, we require revelation to supply the norms; but to exercise them minimally, we need only human reason. Treating your neighbor justly is the minimal way of treating him or her lovingly.

However much the prior moral norms are reconfigured or recontextualized in revelation, they are not substantially altered. Their content remains intact. That is why these basic norms can be honestly kept by those who do not acknowledge, or do not yet acknowledge, the original Giver of natural law. But those who say there is not or cannot be any such Lawgiver deny the transcendent or “metaphysical” aspect of human nature, which human history has shown can never be successfully suppressed.

Formulating these minimal rights and their corresponding duties is the business of natural law discourse as philosophy. But this philosophical discourse can ultimately regard all human rights as entitlements from God and their corresponding duties as commands (mitsvot). These commanded duties are natural law when their formulation accords with rational human nature. Indeed, it is because of these rights that their corresponding duties have been commanded. Maimonides taught that when natural law’s prime origin in God’s creative will is recognized, natural law can then be recognized as the most universally knowable and applicable manifestation of divine law.

Our relationship with God is with the God who purposefully created the whole universe, and who gives us humans our portion therein. Part of that portion is our ability to discern by means of practical reason what is just and what is unjust in our relations with other humans. What we rightly discern here is natural law. My late revered philosophical mentor, Germain Grisez, once called our knowledge of natural law “an ­intellect-sized bite of reality.” Yet without the much larger acknowledgement of the whole universe as God’s creation—a truth that could only be known by its having been revealed to us by God—our commitment to natural law as our most rational modus vivendi would be like clinging to a shrinking island of rationality in an expanding, absurd, purposeless universe.

Due to the influence of Spinoza, Darwin, and the lesser thinkers who follow them in rejecting cosmic teleology, our human-worldly enclave is getting smaller and smaller. And, of course, the absurd universe has no place for a purpose-intending divine Creator, nor for human creatures whom God allows to choose either to cooperate with or to deviate from God’s creative purposes. Only a revelation-based theology can speak confidently of a purposeful cosmos in which our little island of natural law rationality is a participant, not an anomaly. Theology can thus help us address the fear that natural law is some fluke in an otherwise impersonal universe.

The sad acceptance of cosmic purposelessness, by contrast, is evident in the disappointment of those who engage in what could be called “theologically obtuse” public reason and political advocacy. This existential disappointment is especially acute in young secular idealists when they grow older and more cynical and realize that they cannot change the world after all. They have no position outside the world (like Archimedes’ fulcrum) from which to change it—or redeem it. They are among those who look to politics for salvation, who think the ultimate concerns of humans are essentially political, and we humans only satisfied by political victories. But as the Bible puts it: “Do not place your trust in worldly princes, in humans who do not provide salvation” (Ps. 146:3).

For true human flourishing, it is necessary but not sufficient for humans to be homo politicus. When politics is deemed self-sufficient, and when homo politicus proclaims his autonomy—often loudly, in our faces—religious natural law thinkers need to acknowledge our commitment to God the Creator behind all this, and our commitment to God the Redeemer ahead of all this, along with our commitment to God who guides us in the midst of all this. “I [God] am the first; I am also the last” (Isa. 48:12). In the words of my late theological mentor Abraham Joshua Heschel, “Our task is to conquer evils one by one, until the One comes and conquers all evil.”

Let me emphasize again that natural law precepts are not conclusions deduced from theological premises. Natural law is aided by theology in that theology shows natural law its origin and ultimate end; it does not show natural law’s intelligibility, nor its practicality. Even though we do not deduce from our theologically formulated doctrines (Torah) what is to be done or not done in secular space—in what Richard John Neuhaus called “the public square”—these larger doctrines strengthen and elevate our practical judgments concerning what is to be done or not done in specific circumstances. They do so by informing our moral acts, by placing or recontextualizing them in the reality of the created, purposeful cosmos. But our moral acts are not thereby removed or displaced from their more immediate political locale in the world.

Despite being certain that our theologies show us a more adequate source of law than do the modern theories of Hobbes, Rousseau, Kant, and Rawls, religious natural law thinkers should keep our theological certitude mostly to ourselves. We should bring our religious convictions into the public square only when we need to fend off the charge of secularists that our existential commitments not only do not help public reason, but in fact hinder it. This is the view John Rawls eventually came to advocate. In such controversial situations, which we do not seek, but to which we must respond, the best defense is a good offense. We need to show how our religious commitments reinforce and deepen our commitment to the principles any reasonable person would agree are necessary for a just society. Meanwhile, our religious convictions should constantly and explicitly enrich our moral reasoning within our own faith communities, and in dialogue among faith communities. In the public square, we are philosophers; at home, we are theologians; and the two disciplines are quite compatible. We religious natural law thinkers and advocates should practice them both with political savoir faire, philosophical perspicacity, and theological fidelity.

David Novak holds the J. Richard and Dorothy Shiff Chair of Jewish Studies at the University of Toronto. This was a lecture delivered at the annual conference of the James Madison Program of Princeton University on May 14, 2019.