“The Ten Commandments, which constitute an extraordinary path of life and indicate the surest way for living in freedom from slavery to sin, contain a privileged expression of the natural law.” — Compendium of the Social Doctrine of the Church, #22.
“A civilized people is held together by its common understanding of what is virtuous and vicious, noble and base.”– Allan Bloom and Harry Jaffa, Shakespeare’s Politics, 1964. 
“Human freedom is always a freedom shared with others. It is clear that the harmony of freedom can be found only in what is common to all: the truth of the human being, the fundamental message of being itself, exactly the lex naturalis.” — Benedict XVI, “To the International Congress on Natural Moral Law.” 
The headlines in L’Osservatore Romano (English version), for the Holy Father’s lecture on the natural law read as follows: “‘Lex naturalis‘ reflects ‘lex divina.'” As far as I know, this sentence is not found in the comments that Benedict XVI gave in the Clementine Hall to the gathering of the natural law conference. Now, I suppose that this usage of natural law “reflecting” divine law could be defended with some careful distinctions. But normally one would say, at least in the language of St. Thomas, that the natural law reflects the lex aeterna. The lex divina refers rather to revelation, to “positive” divine law.
The only time “divine law” is used in the text is in a citation from Gaudium et Spes about marriage in which it says that “the institution of marriage has been ‘confirmed by the divine law.'” The obvious meaning here is that the natural law was already in place so that the divine law was not the origin of the original understanding of what marriage was. That understanding was already in the natural law through the eternal law. These remarks, however, should not be taken to mean that there is a conflict between the eternal and natural law over against the divine law.
Indeed, in the initial citation from the Compendium of the Social Doctrine of the Church, the relation of the Ten Commandments–which are revelation–to the natural law–which is reason–is that the former reinforces and confirms what is already in some real sense known in the latter. As such, we do not need the Ten Commandments to know what theft, murder, or adultery is. But the Commandments both reinforce our knowledge and strengthen our wills to act according to our reason. Ethical “knowledge” is always related to doing.
Aquinas says that the natural law is the eternal law looked at from the point of view of the creature-subject. Or better, the creature’s very being, his “natural law,” is a reflection of the eternal law that makes him to be this rather than that. He is what he is because of how the eternal law conceived him. Even though Hugo Grotius, in a famous and oft-cited remark, said the “natural law would be the natural law, even if God did not exist,” this is not the Thomist view. The natural law does not create itself to be what it is. The eternal law is the understanding in the mind of God of all those things in their diversity that are outside of God. As such, God did not need to create anything outside of Himself. God could have conceived something but decided never to create it. On the other hand, nothing exists but what is first conceived or anticipated in eternal law. Otherwise something would come from nothing.
The divine law, likewise, need not have been. “Human law” refers to the political or positive laws that men need or find helpful to achieve the practicalities of their social and political nature. When Aquinas talks of the divine law, he asks a very specific question: is it “reasonable,” that is, does it makes sense, for God, with some (to us) intelligible reason, to have given mankind–in addition to eternal, natural, and human law–a divine law?
Here a philosopher, considering the situation, really wants to know the relation of reason and revelation. Are they compatible? The natural law does not exactly “reflect” the divine law. Rather, it explains why natural law, in addition to itself and positive or human law, might “need,” or why it might be advisable to have, further explanations. These explanations were designed to help complete man’s actual purpose in this world. They were designed ultimately to achieve man’s particular destiny, the transcendent inner life of the Trinity offered to him as a gift..
Thus, Aquinas listed the four famous areas in which natural law might conceivably be open to further elucidations. These elaborations would at least make plausible why revelation might in fact have happened. That is, why is it not irrational to accept revelation on these points? What Aquinas was really driving at was thus whether it was “reasonable,” or whether it made sense, that God, without contradicting Himself or without being accused of initial negligence, might take the trouble to teach us more than what we could know by our own limited rational powers? But what was actually revealed in the Old and New Testaments was not “contradictory” to reason actively thinking on itself along its already established lines.
Aquinas thought several arguments could at least suggest to us that God might further instruct us in a way that, when spelled out, would make sense to us. Four reasons were given to consider: 1) that we need a more clear understanding of God than the vague, but valid, notion found in the philosophers by their methods; 2) that the positive law could only deal with external actions whereas the divine law commanded that we also have our inner souls in order (since this is where all disorders originated); 3) that we needed a more careful description of what we ought to do in every day life, hence the commandments; and, finally 4) that we needed to know about heaven and hell, that ultimately unrepentant crimes would be punished and unacknowledged good works would be rewarded. Otherwise, the universe would seem to be poorly made.
The term “divine law” in Aquinas is thus a specialized term. In a sense we could say, more properly, that the natural law, under conditions of time and finiteness, did not reflect adequately the eternal law. Thus, we needed a divine law addressed to our understanding about why we have so much difficulty in observing the natural law of our being. But if it is “natural,” why would we need more guidance? Two reasons are given. One has to do with the very nature of a finite being who has intelligence, and the other with the Fall, which involved us in an original disorder of soul that we repeat when we choose ourselves over what is right.
Be that as it may, the Pope began his lecture by noting man’s increasing capacity “to decipher the rules and structures of matter and in the consequent domination of man over nature.” This reference to a principle of order in matter is a favorite theme of Benedict XVI. He sees its Platonic origins. What is at stake is that when scientists undertake to examine nature, there is something there to find–something that is outside the scientists’ own minds. This is why they can, in fact, check or verify to others their own work to see whether it is true or not. The Holy Father also concludes that this scientific knowledge gives man “domination over nature,” words that recall the passage in Genesis in which man is given “dominion” over all things.
Benedict, likewise, sees a darker side of this “dominion,” as it recalls the project of Bacon that man can seemingly “improve” his estate apart from nature. The Pope next shifts attention from nature itself to the modern “methods” of analyzing it. Here, though he acknowledges the advantages, he is concerned with “method.” “The method that permits us to know ever more deeply the rational structures of matter makes us ever less capable of perceiving the source of this rationality, creative Reason.” What is being said here? Evidently nothing is wrong with knowing more about nature or its “rational structures.” Why then would this scientific method be dangerous? It obscures the question of the origin of nature itself. The method limits itself–a scientific “self-limitation”–to only the nature of mathematical objects, which as such prescind from motion.
“The capacity to see the laws of material being makes us incapable of seeing the ethical message contained in being, a message that tradition calls lex naturalis, natural moral reason.” The method is “reductionist,” that is, it can only see what its presuppositions allow it to see. It does not see all that is there to see. Spiritual and free choices are not “material.” Hence, they not mathematical, or based in matter. They do not appear under the method’s scope or field. Thus, for many people today, the world is “incomprehensible.” Metaphysics, the science of being as such, is excluded. The only thing that exists is that which is a priori assumed and falls under the object of scientific method, that is, mathematics.
Since ethics is not “scientific” in this view, people have a sense of “disorientation,” of guidelessness, of no place to discover what they are unless they are presumed to be only “material.” The Pope thinks this sense of no order is particularly a problem for the young who still must make “fundamental” life choices. This choosing is difficult to do if we have no moral guidance from our own nature and its order. Because of this problem, the Pope sees the need to return to “natural law and to rediscover its truth common to all men.” He then cites Paul to the Romans about the “law written on the heart of man.” The Pope affirms that this law is still accessible today. Its original location in our hearts has not changed as we are still men.
The first principle of this law recalls that already formulated by the philosophers: “to do good and to avoid evil.” We can find this principle in Aristotle or Cicero. This principle is self-evident; that is, one only affirms it by any effort to deny it. Suppose, for example, I say that what is “evil” by natural law standards is “good” (the Machiavellian problem). What have I affirmed? What in effect I do is to say it is “good” to do what is “evil.”
Following Aquinas, the Pope adds that from this first principle of doing good and avoiding evil, all the other principles flow and are connected. That is, each action is defined in terms of good and evil. They are not interchangeable at will. The man who says that it is “good” to do “evil,” says, at the same time, that it is “evil” to do “good.” Otherwise, he would not say anything. No one can escape, then, the question “what is good, particularly what is the human good?”
The first explicit example of doing good and avoiding evil that Benedict gives is “respect for human life from its conception to its natural end, because this good of life is not man’s property but the free gift of God.” This position was similar to an argument already heard in Cicero about suicide, that we should not take our own lives because these lives are from the gods. We do not cause our own “what we are,” our own human being. Nor do we cause that we are to come to be. St. Irenaeus says that “from the beginning God created man out of his own generosity” (Adv. Her. 4). Benedict says the same thing here. This position implies that we do not have “dominion” over what we are as human beings. Rather we discover what we are as given and, by reflection, follow the “law” of our human being..
Secondly, again recalling Aquinas, we have the duty to “seek the truth as the necessary presupposition of every authentic personal maturation.” This inclination includes the duty to seek the truth about God.
Thirdly, there is the question of freedom. Human freedom “is always a freedom shared with others.” Here Benedict makes a point that is, I think, characteristic to his own charism. “The harmony of freedom can be found only in what is common to all: the truth of the human being, the fundamental message of being itself, exactly the lex naturalis.” Freedom is for the sake of being; it does not make the being itself to be what it is. Modern freedom often wants to say “autonomy is freedom”–that we create ourselves. Not only is this dull, but it misses the depths of the being that we already are, a being greater than our own conceptions of ourselves.
Benedict next mentions those two themes of John Paul II, justice and solidarity. Here again the hopes of the poor and the weak are explained precisely in terms of the feelings of justice and solidarity that others have for their plight. This was a theme found in Deus Caritas Est, about active charity as a necessary function in any social order.
Benedict next turns to the term “values,” a very dangerous word in modern German philosophy, as he knows. In Max Weber, and through him in much of modern sociology, a “value” meant precisely a lack of knowledge of any good or a lack of a standard by which we could orient ourselves. Modern social science was designed to tell us how to do whatever we wanted to do, whatever it was. No one could decide which “value” was better or different from any others. Evil and good had the same relativity.
Benedict begins by separating himself from this dubious usage of the word “value.” “In these values (grounded in natural law) are expressed unbreakable and contingent norms that do not depend on the will of the legislator and not even on the consensus that the State can and must give. They are, in fact, norms that precede any human law: as such, they are not subject to modification by anyone.” This is why the natural law is universal. It is not created by the legislator or given final authority by any public consensus.
Benedict next speaks of “ethical imperatives” that flow from the law. The law is meant to be obeyed. It is not merely a statement of fact. The Pope means that these laws indicate, when the circumstances arise, that we should do good and avoid evil in this or that concrete way. Law is in “command form” because it refers to action, the “knowing” part is decided; we need to act or not act in this way or that.
Actions, however, becomes complicated in modern states because we have, more and more, positive (human, civil) laws that “command” us to do what is against the natural law. “In today’s ethics and philosophy of Law, petitions of juridical positivism (i.e., the law is only what the legislator says) are widespread. As a result, legislation often becomes only a compromise between different interests: seeking to transform private interests or wishes into laws that conflict with the duties deriving from social responsibility.” This passage shows a good grasp both of the law school philosophies and the practice of legislatures.
What is the source of any law’s authority or validity, if it is not itself and its own promulgation? “Every juridical methodology, be it on the local or international level, ultimately draws its legitimacy from its rooting in the natural law, in the ethical message inscribed to the actual human being.” It is the actual human being who lives within any legal framework. A “juridical methodology” is one that seeks to explain why it is justified in doing what it commands. It is not its own self-justification.
What is the reason we can call any legal system to explain and justify itself? Why can we object to unjust laws or regimes of terrorism or moral decay? “Natural law is, definitively, the only valid bulwark against the arbitrary power or the deception of ideological manipulation. The knowledge of this law inscribed on the heart of man increases with the progress of the moral conscience” This latter distinction between the natural law that does not change and our knowledge of it that does grow was found in Maritain’s discussion of natural law in his Man and the State.
The Pope understands that a more clear understanding of natural law can occur with reflection and experience. He even says that it is a “duty” of those with “public responsibility” to promote this progress. We are supposed to learn more and more about what is right, about what we are. We are not left isolated when more sophisticated problems arise because natural law is available to confront new problems..
“The law inscribed in our nature is the true guarantee offered to everyone in order to be able to live in freedom and to be respected in their own dignity.” The natural law is not “outside” of us. We can act freely and intelligently. Even when we obey the law, we can understand why there is law and why we obey it. We can also state why a positive law may be immoral, against reason. We have our own resources in our reason that is something that can be addressed to everyone. Benedict XVI has often indicated that he proposes to meet the modern world in precisely this basis, that of Logos, of reason.
Benedict again refers to a theme that seems to have become the special vocation of Catholics to defend: the family. This is the institution with no specific recognition or basis of defense, even in the American Constitution, though we might say that the founders presumed it. But modern individualism does not place the family in the central place that is found in Catholic social thought. No institution is more under fire than the family from almost every angle. Yet, with population decline, immigration, family breakup and crises, it seems clear that it is precisely the violation of family life that is not “working” to bring forth the good claimed by its attackers.
Benedict defines the family by citing Gaudium et Spes. It is the “intimate partnership of life and the love which constitutes the marriage state … established by the Creator and endowed by him with its own proper laws.” Here is where it is noted that the dignity of the family is “confirmed” by “divine law.” What needs to be emphasized is that the family has its own “proper” laws. The state does not define what the family is or give it its structure.
With a kind of stunning logic, Benedict continues, “therefore, no law made by man can override the norm written by the Creator without society becoming dramatically wounded in what constitutes its basic foundations.” We know laws made by man do seek to “override” the norm written by the Creator. Benedict says that society becomes “dramatically wounded.” There can be no doubt that this has happened among us.
In a rather personal remark Benedict adds, “I feel the duty to affirm yet again that not all that is scientifically possible is also ethically licit.” We can do in the name of law or science what we ought not to do while understanding what we are. Human beings are not “objects” of experimentation This was a theme most powerfully argued by C. S. Lewis in his Abolition of Man. Technology without ethical principles can do “violence” to human nature. Nonetheless, “the contribution of science is of primary importance.” The abuses of a thing do not negate against its good uses.
As in other areas, what Benedict is pursuing in this reflection on natural law is an intellectual place where everyone involved can talk of issues based on common principles that are philosophically defined. On this basis, it is possible “to develop a fruitful dialogue between believers and non-believers, between theologians, philosophers, jurists and scientists, which can offer to legislation as well precious material for personal and social life.” The Pope sees natural law as a central basis of “private life and social order”
“A civilized people is held together by a common understanding of what is virtuous and vicious, noble and base.” This is as good a statement of the meaning of natural law as any. One can, however, turn it around. “An uncivilized people is held together by having no common definition of what is virtuous and vicious, noble and base,” of what is good and what is evil. But a “people” with nothing in common except a denial of communality is not a people. It is a collection of isolated individuals, each living in his own world. Many want to define “democracy” in precisely this way, a people held together by no truth, or no possibility of truth except the “truth” that there is no truth. Aristotle would have called this “tyranny.” John Paul II did call it “tyranny.”
“The harmony of freedom can only be found in what is common to all.” There must, finally, be something in what is that all of us can, in reason, discover together, something we find but do not ourselves make. Among these things is our own “natural law,” itself reflective of the eternal law, aided by worthy positive laws, and addressed by divine law. The “natural law” of a human being, Aquinas said, is “what is reasonable.” It has not changed, but we know more about it, including, more and more, what happens to us when we deny it.
 Allan Bloom and Harry Jaffa, Shakespeare’s Politics (Chicago: University of Chicago Press, 1964),
 Benedict XVI, February 12, 2007, L’Osservatore Romano, English, February 21, 2007.