One of those significant references to the natural law that we have had the opportunity to see in the context of the references to the eternal law, comes from St. Augustine's work entitled On Eighty Three Diverse Questions or De Diversis Questionibus Octoginta Tribus:
From this ineffable and sublime arrangement of affairs, then, which is accomplished by divine providence, a natural law [naturalis lex] is, so to speak, inscribed upon the rational soul, so that in the very living out of this life and in their earthly activities people might hold to the tenor of such dispensations." (Boniface Ramsey, tran.).
Hac igitur ineffabili atque sublimi rerum administratione, quae fit per divinam providentiam, quasi transcripta est naturalis lex in animam rationalem, ut in ipsa vitae huius conversatione moribusque terrenis homines talium distributionum imagines servent.
The natural law, in so many words, again makes its appearance in St. Augustine's Commentary on the Sermon on the Mount:
For who but God has written the law of nature (naturale legem) in the hearts of men? that law concerning which the apostle says: "For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: which show the work of the law written in their hearts, their conscience also bearing them witness and their thoughts the meanwhile accusing or else excusing one another, in the day when the Lord shall judge the secrets of men." [Rom. 2:14-16] And therefore, as in the case of every rational soul, which thinks and reasons, even though blinded by passion, we attribute whatever in its reasoning is true, not to itself but to the very light of truth by which, however faintly, it is according to its capacity illuminated, so as to perceive some measure of truth by its reasoning . . .
Quis enim scripsit in cordibus hominum naturalem legem nisi Deus? De qua lege Apostolus dicit: Cum enim gentes, quae legem non habent, naturaliter quae legis sunt faciunt, hi legem non habentes ipsi sibi sunt lex; qui ostendunt opus legis scriptum in cordibus suis, contestante conscientia illorum et inter se invicem cogitationum accusantium aut etiam excusantium, in die qua iudicabit Deus occulta hominum. Quapropter si omnis anima rationalis etiam cupiditate caecata tamen cum cogitat et ratiocinatur, quidquid in ea ratiocinatione verum est non ei tribuendum est sed ipsi lumini veritatis, a quo vel tenuiter pro sui capacitate illustratur, ut verum aliquid in ratiocinando sentiat . . . .
Therefore, let me explain briefly, as well as I can put it in words, the notion of that eternal law which is impressed upon our nature: 'It is that law in virtue of which it is just that all things exist in perfect order.'
Ut igitur breviter aeternae legis notionem, quae impressa nobis est, quantum valeo verbis explicem, ea est qua iustum est ut omnia sint ordinatissima . . .
During the course of that dialogue with Evodius, St. Augustine speaks about the quality of reason that exists in man, and how it distinguishes him from the beasts. Man shares life with vegetative and animal life (nutrition, growth, reproduction, health), and he shares the knowledge that he lives (e.g., senses, movement, even self consciousness). Man has somethings that he does not share with the brutes, such as the ability to laugh or to joke, i.e., risibility. "Anyone with a true discernment of human nature will say that this is a human quality, though of a lower order." De lib. arb., 1.1.18. Man also shows other unique qualities, the desire for glory and lust for power (he mentions love of praise, but had St. Augustine a dog, one wonders how he could have included this as specific to humans. What dog does not seek the praise of his master!). But these latter can make man unhappy if not subjected to reason. It is therefore reason that seems to be the compass of order in man:
Whatever sets man above the beast, whether we call it 'mind' [mens] or 'spirit' [spiritus] or, more correctly, both since we find both terms in Scriptures, if this rules over and commands the other parts that make up man, then man's life is in perfect order [tunc esse hominem ordinatissimum]. . . . We are to think of a man well-ordered, therefore, when his reason rules over these movements of the soul, for we must not speak of right order, of or order at all, when the more perfect is made subject to the less perfect. . . . It follows, therefore, that when reason, [ratio] or mind [mens], or spirit [spiritus], rules over the irrational movements of the soul, then that is in control in man which ought to be, by virtue of the law which we found to be eternal.
Illud est quod volo dicere: hoc quidquid est, quo pecoribus homo praeponitur, sive mens, sive spiritus, sive utrumque rectius appellatur (nam utrumque in divinis Libris invenimus), si dominetur atque imperet caeteris quibuscumque homo constat, tunc esse hominem ordinatissimum. . . . Hisce igitur motibus animae cum ratio dominatur, ordinatus homo dicendus est. Non enim ordo rectus, aut ordo appellandus est omnino, ubi deterioribus meliora subiciuntur . . . . Ratio ista ergo, vel mens, vel spiritus cum irrationales animi motus regit, id scilicet dominatur in homine, cui dominatio lege debetur ea quam aeternam esse comperimus.
For hence it is that even the ungodly think of eternity, and rightly blame and rightly praise many things in the morals of men. And by what rules do they thus judge, except by those wherein they see how men ought to live, even though they themselves do not so live? And where do they see these rules? For they do not see them in their own [moral] nature; since no doubt these things are to be seen by the mind, and their minds are confessedly changeable, but these rules are seen as unchangeable by him who can see them at all; nor yet in the character of their own mind, since these rules are rules of righteousness, and their minds are confessedly unrighteous. Where indeed are these rules written, wherein even the unrighteous recognizes what is righteous, wherein he discerns that he ought to have what he himself has not? Where, then, are they written, unless in the book of that Light which is called Truth? Whence every righteous law is copied and transferred (not by migrating to it, but by being as it were impressed upon it) to the heart of the man that works righteousness; as the impression from a ring passes into the wax, yet does not leave the ring.
. . . . unde omnis lex iusta describitur, et in cor hominis qui operatur iustitiam, non migrando, sed tamquam imprimendo transfertur; sicut imago ex anulo et in ceram transit, et anulum non relinquit.
As was common amongst the Fathers of the Church, St. Augustine links the natural law with the Golden Rule. "[T]his theme of popular ethical teaching found in the New Testament, was popular with the Fathers." Crowe, 66. St. Augustine was no exception. One sees the reference of the natural law in St. Augustine's 25th Sermon on Psalm 118:
No one injures another without at the same time hoping the same will not be done to himself, and in this respect he transgresses the law of nature; the very fact that he does not want to suffer the fate he inflicts on someone else means that he cannot plead ignorance of the natural law. Was this natural law not present in the people of Israel? Certainly it was, for they too were human. They could no more have been without the natural law than they could have been alien to the human condition itself.
Nullus enim est qui faciat alteri iniuriam, nisi qui fieri nolit sibi: et in hoc transgreditur naturae legem, quam non sinitur ignorare, dum id quod facit non vult pati. Numquid autem lex ista naturalis non erat in populo Israel? Erat plane, quoniam et ipsi homines erant: sine lege autem naturali essent, si praeter naturam humani generis esse potuissent. Multo magis ergo praevaricatores facti sunt lege divina, qua naturalis illa sive instaurata, sive aucta, sive firmata est.
Perhaps the best synthesis of St. Augustine's notion of the natural law may be taken from his correspondence. In Letter 157 (Crowe mistakenly cites Letter 158), a letter that he writes to a correspondent named Hilary, St. Augustine outlines his view on the natural law, seeing it in Pauline and Jeremian fashion as written in man's heart, as incorporating the Golden rule, and as supplemented by the positive legislation of the Mosaic law. The letter itself would warrant expansive treatment in itself, but here we shall only provide an exemplary quote:
Hence, since there is also a law in the reason of a human being who already uses free choice, a law naturally written in his heart, by which he is warned that he should not do anything to anyone else that he himself does not want to suffer, all are transgressors according to this law, even those who have not received the law given through Moses.
Proinde quoniam lex est etiam in ratione hominis qui iam utitur arbitrio libertatis, naturaliter in corde conscripta, qua suggeritur ne aliquid faciat quisque alteri quod pati ipse non vult; secundum hanc legem praevaricatores sunt omnes, etiam qui legem per Moysen datam non acceperunt.
Here shall end our patchwork treatment of St. Augustine and his doctrine of the eternal law and natural law. An obvious lacuna in this treatment is the absence of St. Augustine's great work De civitate Dei, On the City of God. However, to do it any sort of justice, that work requires a focus all of its own. Before we take part, however, it might be à propos to provide a synopsis or summary of all these teaching, one from the mind of Étienne Gilson as found in his The Christian Philosophy of Saint Augustine:
There is a law in God which, in Him, is simply God Himself, and to this law everything which is not God is subject. We call it the eternal law. Its content is a prescription of the divine reason or God's will ordering the preservation of the natural order and forbidding its disturbance. This immutable law illumines our conscience as the divine light enlightens our understanding. What the first principles of knowledge, seen in the eternal ideas, are to our reason in the order of knowledge, the first principles of morality are to our conscience in the order of action. There is therefore a kind of law in us also, consisting of the imperative commands of conscience; its rules are so many primary certitudes. We call it the natural law. It derives its certitude from the fact that it is simply a kind of transcript in our souls of the eternal law subsisting immutably in God. Consequently, all the detailed commands of our moral conscience, all the changing acts of legislation governing peoples spring from one and the same law. It is constantly being adapted to meet various changing needs. But in itself it never changes. Everything lawful in the individual and in the city is derived from it. It is truly the law of laws.
The fundamental demand the eternal law imposes on the universe in general and upon man in particular is that everything be perfectly ordered (ut ominia sint ordinatissima). Now in all places and at all times order should have the lower subject to the higher. There is no doubt that, generally speaking, everything created by God is good. From rational creatures to the lowliest of bodies, there is nothing man cannot use lawfully. His difficulty consists in distinguishing between things, all of which are good, but not equally good: he has to weight them, estimate their proper value, subordinate external goods to the body, the body to the soul of man, and then, within the soul, make the senses subject to reason and reason to God.
All english quotations from De libero arbitrio (The Free Choice of the Will) are from the translation of Robert P. Russell, O.S.A. in the text St. Augustine, The Teacher, The Free Choice of the Will, Grace and Free Will (CUA 1968); english quotations from Exposition 25 of Psalm 118 are from Maria Boulding, trans., Exposition of the Psalms 99-120 (New York City Press, 2003). English translation of Letter 157 is taken from Roland Teske, S.J., trans., Letters 156-210 (New York City Press, 2004). All latin quotations are taken from the excellent website on St. Augustine's works: http://www.augustinus.it/latino/.