First, by way of introduction: a delightful scene from Whit Stillman’s recent movie Love and Friendship, in which Sir James Martin attempts to have an erudite conversation with Frederica, Lady Susan’s daughter, as Sir Reginald DeCourcy looks on:

Sir James Martin: Just yesterday, [your mother] cited to me a story from the Bible about a very wise king. This reminded me of many such accounts one learns in childhood. Perhaps most significant in forming one’s principles is that of the old prophet who came down from the mount with tablets, bearing the 12 commandments, which our Lord has taught us to obey without fail. Sir Reginald DeCourcy: 12 commandments. Sir James Martin: Mm. Charles Vernon: Excuse me but, uh, I believe there were only 10. Sir James Martin: Really? Only 10 must be obeyed. Excellent. [chuckles] Well, then, wh… which two to take off? Perhaps the one about the Sabbath. I prefer to hunt. Charles Vernon: Well… Sir James Martin: After that, it becomes tricky. Many of the “shalt nots”– don’t murder, don’t covet thy neighbor’s house, or wife — (laughs) — you– one simply wouldn’t do anyway, because they are be wrong, whether the Lord allows us to take them off or not.

It is telling that the buffoonish Sir James, who does not even know how many Commandments there are, understands their relation to the law of nature better than many modern Christians do: “Many of the thou shalt nots…[o]ne simply wouldn’t do, anyway. Because they are wrong.” What Sir James recognizes is that the laws that are contained in the Decalogue (or the Dodecalogue, as he would have it) are the publication in Israel of principles that are true and binding at all times and in all places, whether Moses had ever brought the Commandments down from Sinai or not.

And this is, in fact, the classical Protestant understanding. According to this line of thinking, the natural law–by which I mean the basic principles of knowing what things should be done and what should be avoided, or the ability to distinguish between good and evil, imprinted on man’s heart by God– is the same in its principles as the moral law, and the moral law is summarized in the Ten Commandments. This is a position that is shared by both the Lutheran and the Reformed traditions, as will be demonstrated by what follows.

First, let us look at a couple of examples on the Lutheran side. One might cite, first, Philip Melanchthon from the 1559 edition of The Chief Theological Topics:

As light has been set before our eyes by God, likewise certain knowledge has been implanted in the minds of men by which they understand and evaluate many things. The philosophers call this light the knowledge of the first principles, which they also call common notions or preconceptions.

But what about the Fall? Doesn’t sin destroy man’s natural knowledge? To be sure, Melanchthon does not mean that such natural knowledge has not been weakened by sin; it has:

[E]ven though the knowledge of the truth has been strongly impressed upon men that there is one God who is the eternal mind, the creator and preserver of things, who is wise, good, just, etc., and that this God is to be obeyed in keeping with the difference between honorable and evil things, yet this knowledge of the truth is suppressed and rejected in unrighteousness, that is, it is held captive and does not have the rule, but rather unrighteousness rules in opposition to this knowledge, by turning away man’s will from God, by contempt for Him, by confidence in human abilities, and finally by various desires which conflict with the light which has been divinely kindled in our minds.

It has been weakened, then. Notice what this does not mean, however: it does not mean that all matters of human law and morality suddenly become subject to human opinion, it being impossible to determine from any “outside” vantage point whether a particular law is just or vicious. In other words, it does not mean that all natural knowledge (and all natural responsibility) has been destroyed:

Thus the philosophers (when they saw that the assent of man was very weak and that men were carried away with great force to different pleasures) asked whether what was right and what was wrong were to be determined by nature or merely by human opinion. To have doubt on such a matter is shameful and disgraceful, just as if one were to ask whether two times four is eight is a matter of nature or merely an accident. The divine light in the minds of men must not be extinguished; rather, the mind must be stirred up and strengthened in order that it may recognize the first principles of action and embrace them and to determine that the immutable decrees of God are just as sure and certain as the visible principles.

Melanchthon thinks, in short, that the principles of the law of nature are knowable even given sin. Given that that is the case, we should be able to define this law of nature. How does Melanchthon do it?

The law of nature is the knowledge of the divine law which has been grafted into the nature of man. For this reason man is said to have been created in the image of God, because in him shone the image, that is, the knowledge of God and the likeness to the mind of God, that is, the understanding of the difference between the honorable and the shameful; and the powers of man concurred or agreed with this knowledge. The will had been turned to God before the fall, the true knowledge of God glowed in man’s mind, and in his will was love toward God….Although in this corruption of our nature the image of God has been so deformed that the knowledge of Him does not shine forth like it did, yet the knowledge does remain, but our heart contends against it and our doubts arise because of certain things which seem to conflict with this knowledge.

A couple of things stand out: The content of the natural law is the same for Melanchthon as the content of the “divine law.” Our access to it is predicated on our having been made in the image of God. The Fall does not utterly destroy the image, but it does mar it; correspondingly, the Fall therefore corrupts our knowledge of the natural law, but it does not obliterate it. Though the Fall has epistemological consequences, we should not forget that a large part of man’s postlapsarian trouble is also moral and dispositional: our hearts contend against the knowledge of God, as Paul teaches in Romans 1. Nevertheless, all are still accountable to this law that is implanted in the minds of all by God himself.

Melanchthon then proceeds with with an exposition of the law of nature in the order of the commandments of the Decalogue (he thinks that those of the First Table “are not as clear as those which follow which refer to civil life,” but they are still knowable to man, even in his fallen state). This method of discussion for Melanchthon is not arbitrary:

In reviewing the laws of nature I have followed the order of the Decalogue, for this order is clearest and shows the way which our own reason points out for us to follow. But regardless of the order and the number, the substance is the same, if something foreign does not confuse things. Further, it is beneficial to follow this order so that the agreement of the laws of nature with the Decalogue may be evident, and it is useful for many reasons that this be kept in view: First, in order that we may understand that the laws of nature themselves are also divinely instituted and that we may stress and correctly understand that the philosophers and law-givers approve of them and agree with them, and in order that we may reject statements contrary to this. It was for this reason that the divine law was proclaimed from heaven so that God might testify that He is the author of this natural knowledge and that He demands obedience in accordance with this knowledge and that He is accusing the human race because of its stubbornness.

Though in our day it is customary to treat natural law and the Decalogue as two different things (recall all the controversy surrounding Judge Roy Moore; I note the case only to observe that many Christians who favor a natural-law ordering of positive law are also opposed to public displays of the Ten Commandments), for Melanchthon they are identical in content: “Our own reason” points to the same principles as those on which the Ten Commandments are based–all ten, not just six of them.

Melanchthon was not unique in holding to this position. In fact, the position was utterly pedestrian and uncontroversial. For instance, here is how his (unjustly forgotten) disciple Niels Hemmingsen puts the matter in his “Assertions on the Law of God and the Proper Definition of the Gospel”:

Although the word “law” means rather many things in Scripture, nevertheless here I only want to be understood the part that we call the “Decalogue” from the number of its commandments and the “moral law” from its common use. This divine law, which is also called [the law] of nature, was born together with the first men–[the law] that, imprinted on their minds, orders that God must be worshiped and men must be loved.

Notice all of the terms Hemmingsen equates. The Decalogue, the moral law, the divine law, the natural law: all have the same content. Again, this applies to both tables of the law, and not just to the Second Table. Everyone knows by nature that “God must be worshiped and men must be loved.”

Melanchthon and Hemmingsen were both Lutherans. Do we find something similar when we turn to the Reformed? Indeed, we do.

Take, for instance, the Italian Reformed Thomist Girolamo Zanchi: though in other respects his approach to natural law is quite different from Melanchthon’s, they are in agreement with respect to the basic point set out above. In his eighth thesis concerning natural law, he defines it as follows:

Natural law is the will of God, and, consequently, the divine rule and principle for knowing what to do and what not to do. It is, namely, the knowledge of what is good or bad, fair or unfair, upright or shameful, that was inscribed upon the hearts of all people by God himself also after the Fall. For this reason, we are all universally taught what activities should be pursued and what should be avoided; that is, to do one thing and to avoid another, and we know that we are obligated and pushed to act for the glory of God, our own good, and the welfare of our neighbor both in private and in public.

Natural law is once again theocentric: It is the “will of God” and a “divine rule” by which all people know that they are “obligated and pushed to act for the glory of God.” Although Zanchi does not address the Decalogue directly in his section on natural law, that is not because the two are unrelated. In his discussion of Thesis 11, he writes:

Yet, because the Decalogue defines and describes the same things that are called natural law, the Ten Commandments themselves are often called “natural law.” Therefore, I will not here describe what sins against natural law are included because that same thing should be done in the explanation of the Decalogue.

Once again: The Decalogue–that is, all Ten Commandments–are equivalent in content to the natural law. As another example, consider what John Calvin has to say in Institutes 2.8.1:

Moreover, the very things contained in the two tables are, in a manner, dictated to us by that internal law, which, as has been already said, is in a manner written and stamped on every heart. For conscience, instead of allowing us to stifle our perceptions, and sleep on without interruption, acts as an inward witness and monitor, reminds us of what we owe to God, points out the distinction between good and evil, and thereby convicts us of departure from duty. But man, being immured in the darkness of error, is scarcely able, by means of that natural law, to form any tolerable idea of the worship which is acceptable to God. At all events, he is very far from forming any correct knowledge of it. In addition to this, he is so swollen with arrogance and ambition, and so blinded with self-love, that he is unable to survey, and, as it were, descend into himself, that he may so learn to humble and abase himself, and confess his misery. Therefore, as a necessary remedy, both for our dullness and our contumacy, the Lord has given us his written Law, which, by its sure attestations, removes the obscurity of the law of nature, and also, by shaking off our lethargy, makes a more lively and permanent impression on our minds.

Calvin takes rather a dim view in this passage of the “cash-value,” as it were, of the natural law for man in his fallen state–dimmer, perhaps, than what we have seen so far. Nevertheless, that impression should not obscure what he does affirm: that natural law exists; that it is universally known and given to every human being by way of conscience; and that the Ten Commandments are given to clarify for fallen man that very same natural law. Once again, Calvin equates the universally-known law of nature with both Tables. The Decalogue, then, is the same as the natural law, which is also the same as the moral law, and the natural/moral law ought to serve as the basis for all positive law, according to Calvin in Institutes 4.20.16:

Now, as it is evident that the law of God which we call moral, is nothing else than the testimony of natural law, and of that conscience which God has engraven on the minds of men, the whole of this equity of which we now speak is prescribed in it. Hence it alone ought to be the aim, the rule, and the end of all laws. Wherever laws are formed after this rule, directed to this aim, and restricted to this end, there is no reason why they should be disapproved by us, however much they may differ from the Jewish law, or from each other (August. de Civit. Dei, Lib. 19 c. 17).

What we find in Zanchi and Calvin long remained standard Reformed teaching. One finds it long after the death of Calvin, for example, in the work of 17th century theologian Francis Turretin (Institutes of Elenctic Theology 11.2.16):

Fourth, the moral law (which is the pattern of God’s image in man) ought to correspond with the eternal and archetypal law in God, since it is its copy and shadow (aposkimation), in which he has manifested his justice and holiness. Hence we cannot conform ourselves to the image of God (to the imitation of which Scripture so often exhorts us) except by regulating our lives in accordance with the precepts of this law. So when its observation is enjoined, the voice is frequently heard, “Be ye holy, for I am holy.” Now this law is immutable and perpetual. Therefore the moral law (its ectype) must necessarily also be immutable.

The moral law, which Turretin calls the “pattern” of the divine image in man, cannot be changed and must regulate the lives of all people at all times. He goes on to expand upon the point in the following section (11.2.17):

Fifth, the moral law is the same as to substance with the natural, which is immutable and founded upon the rational nature; both because the sum of the law (which is exhausted by the love of God and of our neighbor) is impressed upon man by nature and because all its precepts are derived from the light of nature and nothing is found in them which is not taught be sound reason; nothing which does not pertain to all nations in every age; nothing which is not necessary for human nature to follow in order to attain its end. Therefore it ought to be of perpetual right because the rational nature is always the same and like itself. Hence what is founded upon it must also be such. If by the sin of man the rational nature was changed in the concrete and subjectively, the law was not forthwith altered in the abstract and objectively.

Though Turretin does not refer directly to the Ten Commandments in this passage, it is clear from his reference to “the sum of the law” (which Christ in fact uses as a sum of the Decalogue) that yet again all three (moral law, natural law, and the Ten Commandments) are the same in content, and their principles binding on “all nations in every age.” If man ceases to follow these principles, according to Turretin, he cannot attain his end–that is, he cannot reach the goal for which he was created, nor, by implication, can human societies reach the goal for which they were established.

In every instance we have examined, we can see that the content of the Decalogue and the law of nature are the same at the level of principle. The fact that the Decalogue was given to Israel in particular, as the preface to the Ten Commandments makes plain, should not be allowed to obscure this fact. That God gave the law inscribed on tablets of stone to a particular people as part of a particular covenantal administration does not render the commandments arbitrary, or less universal and less binding on all people, even if the admixture of ceremony in the Ten Commandments is not a matter of universal law.

This should be obvious: the Lord does not condone murder so long as you happen not to be in the covenant community. No less does he condone polytheism or idolatry. As B.B. Warfield says (in an essay on the Sabbath–he shows himself to to be somewhat less lax on the Fourth Commandment than Sir James Martin above), “There is no duty imposed upon the Israelite in the Ten Commandments, which is not equally incumbent upon all men, everywhere. These commandments are but the positive publication to Israel of the universal human duties, the common morality of mankind.”

For this reason, the Protestant tradition in both its Lutheran and Reformed streams has traditionally recognized the substantial identity of the law of nature and the Decalogue, or moral law, and its consequent supremacy over all peoples and all human laws. Whatever disagreements these two sub-traditions have on other matters, they are in agreement on this point. And given our current cultural confusion and inability to give a coherent ground for the authority of positive law, rigorous ressourcement of the tradition in this matter is not just desirable; it is essential.