St. Augustine, John of Salisbury, St. Thomas Aquinas on Political Authority


St. Augustine (A.D. 354-430)

City of God (A.D. 416)

Trans. Marcus Dods, D.D.

Book Nineteen (selections)


Chapter 13.— Of the Universal Peace Which the Law of Nature Preserves Through All Disturbances, and by Which Every One Reaches His Desert in a Way Regulated by the Just Judge.

The peace of the body then consists in the duly proportioned arrangement of its parts.  The peace of the irrational soul is the harmonious repose of the appetites, and that of the rational soul the harmony of knowledge and action. ; The peace of body and soul is the well-ordered and harmonious life and health of the living creature.  Peace between man and God is the well-ordered obedience of faith to eternal law. ; Peace between man and man is well-ordered concord.  Domestic peace is the well-ordered concord between those of the family who rule and those who obey.  Civil peace is a similar concord among the citizens.  The peace of the celestial city is the perfectly ordered and harmonious enjoyment of God, and of one another in God.  The peace of all things is the tranquillity of order.  Order is the distribution which allots things equal and unequal, each to its own place.  And hence, though the miserable, in so far as they are such, do certainly not enjoy peace, but are severed from that tranquillity of order in which there is no disturbance, nevertheless, inasmuch as they are deservedly and justly miserable, they are by their very misery connected with order.  They are not, indeed, conjoined with the blessed, but they are disjoined from them by the law of order.  And though they are disquieted, their circumstances are notwithstanding adjusted to them, and consequently they have some tranquillity of order, and therefore some peace.  But they are wretched because, although not wholly miserable, they are not in that place where any mixture of misery is impossible.  They would, however, be more wretched if they had not that peace which arises from being in harmony with the natural order of things.  When they suffer, their peace is in so far disturbed; but their peace continues in so far as they do not suffer, and in so far as their nature continues to exist. ; As, then, there may be life without pain, while there cannot be pain without some kind of life, so there may be peace without war, but there cannot be war without some kind of peace, because war supposes the existence of some natures to wage it, and these natures cannot exist without peace of one kind or other.

And therefore there is a nature in which evil does not or even cannot exist; but there cannot be a nature in which there is no good.  Hence not even the nature of the devil himself is evil, in so far as it is nature, but it was made evil by being perverted.  Thus he did not abide in the truth, John 8:44 but could not escape the judgment of the Truth; he did not abide in the tranquillity of order, but did not therefore escape the power of the Ordainer. ; The good imparted by God to his nature did not screen him from the justice of God by which order was preserved in his punishment; neither did God punish the good which He had created, but the evil which the devil had committed.  God did not take back all He had imparted to his nature, but something He took and something He left, that there might remain enough to be sensible of the loss of what was taken.  And this very sensibility to pain is evidence of the good which has been taken away and the good which has been left.  For, were nothing good left, there could be no pain on account of the good which had been lost.  For he who sins is still worse if he rejoices in his loss of righteousness.  But he who is in pain, if he derives no benefit from it, mourns at least the loss of health.  And as righteousness and health are both good things, and as the loss of any good thing is matter of grief, not of joy,— if, at least, there is no compensation, as spiritual righteousness may compensate for the loss of bodily health,— certainly it is more suitable for a wicked man to grieve in punishment than to rejoice in his fault.  As, then, the joy of a sinner who has abandoned what is good is evidence of a bad will, so his grief for the good he has lost when he is punished is evidence of a good nature. ; For he who laments the peace his nature has lost is stirred to do so by some relics of peace which make his nature friendly to itself.  And it is very just that in the final punishment the wicked and godless should in anguish bewail the loss of the natural advantages they enjoyed, and should perceive that they were most justly taken from them by that God whose benign liberality they had despised. ; God, then, the most wise Creator and most just Ordainer of all natures, who placed the human race upon earth as its greatest ornament, imparted to men some good things adapted to this life, to wit, temporal peace, such as we can enjoy in this life from health and safety and human fellowship, and all things needful for the preservation and recovery of this peace, such as the objects which are accommodated to our outward senses, light, night, the air, and waters suitable for us, and everything the body requires to sustain, shelter, heal, or beautify it:  and all under this most equitable condition, that every man who made a good use of these advantages suited to the peace of this mortal condition, should receive ampler and better blessings, namely, the peace of immortality, accompanied by glory and honor in an endless life made fit for the enjoyment of God and of one another in God; but that he who used the present blessings badly should both lose them and should not receive the others.


Chapter 14.— Of the Order and Law Which Obtain in Heaven and Earth, Whereby It Comes to Pass that Human Society Is Served by Those Who Rule It.


The whole use, then, of things temporal has a reference to this result of earthly peace in the earthly community, while in the city of God it is connected with eternal peace.  And therefore, if we were irrational animals, we should desire nothing beyond the proper arrangement of the parts of the body and the satisfaction of the appetites,— nothing, therefore, but bodily comfort and abundance of pleasures, that the peace of the body might contribute to the peace of the soul.  For if bodily peace be awanting, a bar is put to the peace even of the irrational soul, since it cannot obtain the gratification of its appetites. ; And these two together help out the mutual peace of soul and body, the peace of harmonious life and health.  For as animals, by shunning pain, show that they love bodily peace, and, by pursuing pleasure to gratify their appetites, show that they love peace of soul, so their shrinking from death is a sufficient indication of their intense love of that peace which binds soul and body in close alliance.  But, as man has a rational soul, he subordinates all this which he has in common with the beasts to the peace of his rational soul, that his intellect may have free play and may regulate his actions, and that he may thus enjoy the well-ordered harmony of knowledge and action which constitutes, as we have said, the peace of the rational soul.  And for this purpose he must desire to be neither molested by pain, nor disturbed by desire, nor extinguished by death, that he may arrive at some useful knowledge by which he may regulate his life and manners.  But, owing to the liability of the human mind to fall into mistakes, this very pursuit of knowledge may be a snare to him unless he has a divine Master, whom he may obey without misgiving, and who may at the same time give him such help as to preserve his own freedom.  And because, so long as he is in this mortal body, he is a stranger to God, he walks by faith, not by sight; and he therefore refers all peace, bodily or spiritual or both, to that peace which mortal man has with the immortal God, so that he exhibits the well-ordered obedience of faith to eternal law. ; But as this divine Master inculcates two precepts,— the love of God and the love of our neighbor,— and as in these precepts a man finds three things he has to love,— God, himself, and his neighbor,— and that he who loves God loves himself thereby, it follows that he must endeavor to get his neighbor to love God, since he is ordered to love his neighbor as himself.  He ought to make this endeavor in behalf of his wife, his children, his household, all within his reach, even as he would wish his neighbor to do the same for him if he needed it; and consequently he will be at peace, or in well-ordered concord, with all men, as far as in him lies. ; And this is the order of this concord, that a man, in the first place, injure no one, and, in the second, do good to every one he can reach.  Primarily, therefore, his own household are his care, for the law of nature and of society gives him readier access to them and greater opportunity of serving them.  And hence the apostle says, Now, if any provide not for his own, and specially for those of his own house, he has denied the faith, and is worse than an infidel. 1 Timothy 5:8   This is the origin of domestic peace, or the well-ordered concord of those in the family who rule and those who obey.  For they who care for the rest rule,— the husband the wife, the parents the children, the masters the servants; and they who are cared for obey,— the women their husbands, the children their parents, the servants their masters.  But in the family of the just man who lives by faith and is as yet a pilgrim journeying on to the celestial city, even those who rule serve those whom they seem to command; for they rule not from a love of power, but from a sense of the duty they owe to others— not because they are proud of authority, but because they love mercy.

John of Salisbury (A.D. 1120-1180)

Trans. John Dickinson

Book Four (selections)


Between a tyrant and a prince there is this single or chief difference, that the latter obeys the law and rules the people by its dictates, accounting himself as but their servant. It is by virtue of the law that he makes good his claim to the foremost and chief place in the management of the affairs of the commonwealth and in the bearing of its burdens; and his elevation over others consists in this, that whereas private men are held responsible only for their private affairs, on the prince fall the burdens of the whole community. Wherefore deservedly there is conferred on him, and gathered together in his hands, the power of all his subjects, to the end that he may be sufficient unto himself in seeking and bringing about the advantage of each individually, and of all; and to the end that the state of the human commonwealth may be ordered in the best possible manner, seeing that each and all are members one of another. Wherein we indeed but follow nature, the best guide of life; for nature has gathered together all the senses of her microcosm or little world, which is man, into the head, and has subjected all the members in obedience to it in such wise that they will all function properly so long as they follow the guidance of the head, and the head remains sane. Therefore the prince stands on a pinnacle which is exalted and made splendid with all the great and high privileges which he deems necessary for himself. And rightly so, because nothing is more advantageous to the people than that the needs of the prince should be fully satisfied; since it is impossible that his will should be found opposed to justice. Therefore, according to the usual definition, the prince is the public power, and a kind of likeness on earth of the divine majesty. Beyond doubt a large share of the divine power is shown to be in princes by the fact that at their nod men bow their necks and for the most part offer up their heads to the axe to be struck off, and, as by a divine impulse, the prince is feared by each of those over whom he is set as an object of fear. And this I do not think could be, except as a result of the will of God. For all power is from the Lord God, and has been with Him always, and is from everlasting. The power which the prince has is therefore from God, for the power of God is never lost, nor severed from Him, but He merely exercises it through a subordinate hand, making all things teach His mercy or justice. "Who, therefore, resists the ruling power, resists the ordinance of God," [Romans 13:2] in whose hand is the authority of conferring that power, and when He so desires, of withdrawing it again, or diminishing it. For it is not the ruler's own act when his will is turned to cruelty against his subjects, but it is rather the dispensation of God for His good pleasure to punish or chasten them. Thus during the Hunnish persecution, Attila, on being asked by the reverend bishop of a certain city who he was, replied, "I am Attila, the scourge of God." Whereupon it is written that the bishop adored him as representing the divine majesty. "Welcome," he said, "is the minister of God," and "Blessed is he that cometh in the name of the Lord," and with sighs and groans he unfastened the barred doors of the church, and admitted the persecutor through whom he attained straightway to the palm of martyrdom. For he dared not shut out the scourge of God, knowing that His beloved Son was scourged, and that the power of this scourge which had come upon himself was as nought except it came from God. If good men thus regard power as worthy of veneration even when it comes as a plague upon the elect, who should not venerate that power which is instituted by God for the punishment of evil-doers and for the reward of good men, and which is promptest in devotion and obedience to the laws? To quote the words of the Emperor, "it is indeed a saying worthy of the majesty of royalty that the prince acknowledges himself bound by the Laws." [Justinian, Codex I.14.4] For the authority of the prince depends upon the authority of justice and law; and truly it is a greater thing than imperial power for the prince to place his government under the laws, so as to deem himself entitled to do nought which is at variance with the equity of justice.


Princes should not deem that it detracts from their princely dignity to believe that the enactments of their own justice are not to be preferred to the justice of God, whose justice is an everlasting justice, and His law is equity. Now equity, as the learned jurists define it, is a certain fitness of things which compares all things rationally, and seeks to apply like rules of right and wrong to like cases, being impartially disposed toward all persons, and allotting to each that which belongs to him. Of this equity the interpreter is the law, to which the will and intention of equity and justice are known. Therefore Crisippus asserted that the power of the law extends over all things, both divine and human, and that it accordingly presides over all goods and ills, and is the ruler and guide of material things as well as of human beings. To which Papinian, a man most learned in the law, and Demosthenes, the great orator, seem to assent, subjecting all men to its obedience because all law is, as it were, a discovery, and a gift from God, a precept of wise men, the corrector of excesses of the will, the bond which knits together the fabric of the state, and the banisher of crime; [Digest I.3.1-2] and it is therefore fitting that all men should live according to it who lead their lives in a corporate political body. All are accordingly bound by the necessity of keeping the law, unless perchance there is any who can be thought to have been given the license of wrong-doing. However, it is said that the prince is absolved from the obligations of the law; but this is not true in the sense that it is lawful for him to do unjust acts, but only in the sense that his character should be such as to cause him to practice equity not through fear of the penalties of the law but through love of justice; and should also be such as to cause him from the same motive to promote the advantage of the commonwealth, and in all things to prefer the good of others before his own private will. Who, indeed, in respect of public matters can properly speak of the will of the prince at all, since therein he may not lawfully have any will of his own apart from that which the law or equity enjoins, or the calculation of the common interest requires? For in these matters his will is to have the force of a judgment; and most properly that which pleases him therein has the force of law, because his decision may not be at variance with the intention of equity. "From thy countenance," says the Lord, "let my judgment go forth, let shine eyes look upon equity"; [Psalm 17:2] for the uncorrupted judge is one whose decision, from assiduous contemplation of equity, is the very likeness thereof. The prince accordingly is the minister of the common interest and the bond-servant of equity, and he bears the public person in the sense that he punishes the wrongs and injuries of all, and all crimes, with even-handed equity. His rod and staff also, administered with wise moderation, restore irregularities and false departures to the straight path of equity, so that deservedly may the Spirit congratulate the power of the prince with the words, "Thy rod and thy staff, they have comforted me." [Psalm 23:4] His shield, too, is strong, but it is a shield for the protection of the weak, and one which wards off powerfully the darts of the wicked from the innocent. Those who derive the greatest advantage from his performance of the duties of his office are those who can do least for themselves, and his power is chiefly exercised against those who desire to do harm. Therefore not without reason he bears a sword, wherewith he sheds blood blamelessly, without becoming thereby a man of blood, and frequently puts men to death without incurring the name or guilt of homicide. For if we believe the great Augustine, David was called a man of blood not because of his wars, but because of Uria. And Samuel is nowhere described as a man of blood or a homicide, although he slew Agag, the fat king of Amalech. Truly the sword of princely power is as the sword of a dove, which contends without gall, smites without wrath, and when it fights, yet conceives no bitterness at all. For as the law pursues guilt without any hatred of persons, so the prince most justly punishes offenders from no motive of wrath but at the behest, and in accordance with the decision, of the passionless law. For although we see that the prince has lictors of his own, we must yet think of him as in reality himself the sole or chief lictor, to whom is granted by the law the privilege of striking by a subordinate hand. If we adopt the Opinion of the Stoics, who diligently trace down the reason for particular words, "lictor" means "legis ictor," or "hammer of the law," because the duty of his office is to strike those who the law adjudges shall be struck. Wherefore anciently, when the sword hung over the head of the convicted criminal, the command was wont to be given to the officials by whose hand the judge punishes evil-doers, "Execute the sentence of the law," or "Obey the law," to the end that the misery of the victim might be mitigated by the calm reasonableness of the words.
This sword, then, the prince receives from the hand of the Church, although she herself has no sword of blood at all. Nevertheless she has this sword, but she uses it by the hand of the prince, upon whom she confers the power of bodily coercion, retaining to herself authority over spiritual things in the person of the pontiffs. The prince is, then, as it were, a minister of the priestly power, and one who exercises that side of the sacred offices which seems unworthy of the hands of the priesthood. For every office existing under, and concerned with the execution of, the sacred laws is really a religious office, but that is inferior which consists in punishing crimes, and which therefore seems to be typified in the person of the hangman. Wherefore Constantine, most faithful emperor of the Romans, when he had convoked the council of priests at Nicaea, neither dared to take the chief place for himself nor even to sit among the presbyters, but chose the hindmost seat. Moreover, the decrees which he heard approved by them he reverenced as if he had seen them emanate from the judgment-seat of the divine majesty. Even the rolls of petitions containing accusations against priests which they brought to him in a steady stream he took and placed in his bosom without opening them. And after recalling them to charity and harmony, he said that it was not permissible for him, as a man, and one who was subject to the judgment of priests, to examine cases touching gods, who cannot be judged save by God alone. And the petitions which he had received he put into the fire without even looking at them, fearing to give publicity to accusations and censures against the fathers, and thereby incur the curse of Cham, the undutiful son, who did not hide his father's shame. Wherefore he said, as is narrated in the writings of Nicholas the Roman pontiff, "Verily if with mine own eyes I had seen a priest of God, or any of those who wear the monastic garb, sinning, I would spread my cloak and hide him, that he might not be seen of any." Also Theodosius, the great emperor, for a merited fault, though not so grave a one, was suspended by the priest of Milan from the exercise of his regal powers and from the insignia of his imperial office, and patiently and solemnly he performed the penance for homicide which was laid upon him. Again, according to the testimony of the teacher of the gentiles, greater is he who blesses man than he who is blessed; [Hebrews 7:7] and so he in whose hands is the authority to confer a dignity excels in honor and the privileges of honor him upon whom the dignity itself is conferred. Further, by the reasoning of the law it is his right to refuse who has the power to grant, and he who can lawfully bestow can lawfully take away. [Digest I.17.3] Did not Samuel pass sentence of deposition against Saul by reason of his disobedience, and supersede him on the pinnacle of kingly rule with the lowly son of Ysai? [Jesse] But if one who has been appointed prince has performed duly and faithfully the ministry which he has undertaken, as great honor and reverence are to be shown to him as the head excels in honor all the members of the body. Now he performs his ministry faithfully when he is mindful of his true status, and remembers that he bears the person of the universitas of those subject to him; and when he is fully conscious that he owes his life not to himself and his own private ends, but to others, and allots it to them accordingly, with duly ordered charity and affection. Therefore he owes the whole of himself to God, most of himself to his country, much to his relatives and friends, very little to foreigners, but still somewhat. He has duties to the very wise and the very foolish, to little children and to the aged. Supervision over these classes of persons is common to all in authority, both those who have care over spiritual things and those who exercise temporal jurisdiction. Wherefore Melchisedech, the earliest whom the Scripture introduces as both king and priest (to say nought at present concerning the mystery wherein he prefigures Christ, who was born in heaven without a mother and on earth without a father); of him, I say, we read that he had neither father nor mother, not because he was in fact without either, but because in the eyes of reason the kingly power and the priestly power are not born of flesh and blood, Since in bestowing either, regard for ancestry ought not to prevail over merits and virtues, but only the wholesome wishes of faithful subjects should prevail; and when anyone has ascended to the supreme exercise of either power, he ought wholly to forget the affections of flesh and blood, and do only that which is demanded by the safety and welfare of his subjects. And so let him be both father and husband to his subjects, or, if he has known some affection more tender still, let him employ that; let him desire to be loved rather than feared, and show himself to them as such a man that they will out of devotion prefer his life to their own, and regard his preservation and safety as a kind of public life; and then all things will prosper well for him, and a small bodyguard will, in case of need, prevail by their loyalty against innumerable adversaries. For love is strong as death; and the wedge [a military formation] which is held together by strands of love is not easily broken. . . .

Source: The Statesman’s Book of John of Salisbury. Translated by John Dickinson. New York: Alfred A. Knopf, 1927.

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© Paul Halsall, October 1998



St. Thomas Aquinas (1225-1275)

The Summa Theologica

(Benziger Bros. edition, 1947)
Translated by
Fathers of the English Dominican Province

(First Part of the Second Part) 




   We must now consider the various kinds of law: under which head there are six points of inquiry:

    (1) Whether there is an eternal law?

    (2) Whether there is a natural law?

    (3) Whether there is a human law?

    (4) Whether there is a Divine law?

    (5) Whether there is one Divine law, or several?

    (6) Whether there is a law of sin?


Article 1: Whether there is an eternal law?


  Objection 1: It would seem that there is no eternal law. Because every law is imposed on someone. But there was not someone from eternity on whom a law could be imposed: since God alone was from eternity. Therefore no law is eternal.

  Objection 2: Further, promulgation is essential to law. But promulgation could not be from eternity: because there was no one to whom it could be promulgated from eternity. Therefore no law can be eternal.

  Objection 3: Further, a law implies order to an end. But nothing ordained to an end is eternal: for the last end alone is eternal. Therefore no law is eternal.

  On the contrary, Augustine says (De Lib. Arb. i, 6): "That Law which is the Supreme Reason cannot be understood to be otherwise than unchangeable and eternal."

  I answer that, As stated above (Question [90], Article [1], ad 2; Articles [3],4), a law is nothing else but a dictate of practical reason emanating from the ruler who governs a perfect community. Now it is evident, granted that the world is ruled by Divine Providence, as was stated in the FP, Question [22], Articles [1],2, that the whole community of the universe is governed by Divine Reason. Wherefore the very Idea of the government of things in God the Ruler of the universe, has the nature of a law. And since the Divine Reason's conception of things is not subject to time but is eternal, according to Prov. 8:23, therefore it is that this kind of law must be called eternal.

  Reply to Objection 1: Those things that are not in themselves, exist with God, inasmuch as they are foreknown and preordained by Him, according to Rm. 4:17: "Who calls those things that are not, as those that are." Accordingly the eternal concept of the Divine law bears the character of an eternal law, in so far as it is ordained by God to the government of things foreknown by Him.

  Reply to Objection 2: Promulgation is made by word of mouth or in writing; and in both ways the eternal law is promulgated: because both the Divine Word and the writing of the Book of Life are eternal. But the promulgation cannot be from eternity on the part of the creature that hears or reads.

  Reply to Objection 3: The law implies order to the end actively, in so far as it directs certain things to the end; but not passively---that is to say, the law itself is not ordained to the end---except accidentally, in a governor whose end is extrinsic to him, and to which end his law must needs be ordained. But the end of the Divine government is God Himself, and His law is not distinct from Himself. Wherefore the eternal law is not ordained to another end.


Article 2: Whether there is in us a natural law?


Objection 1: It would seem that there is no natural law in us. Because man is governed sufficiently by the eternal law: for Augustine says (De Lib. Arb. i) that "the eternal law is that by which it is right that all things should be most orderly." But nature does not abound in superfluities as neither does she fail in necessaries. Therefore no law is natural to man.

  Objection 2: Further, by the law man is directed, in his acts, to the end, as stated above (Question [90], Article [2]). But the directing of human acts to their end is not a function of nature, as is the case in irrational creatures, which act for an end solely by their natural appetite; whereas man acts for an end by his reason and will. Therefore no law is natural to man.

  Objection 3: Further, the more a man is free, the less is he under the law. But man is freer than all the animals, on account of his free-will, with which he is endowed above all other animals. Since therefore other animals are not subject to a natural law, neither is man subject to a natural law.

  On the contrary, A gloss on Rm. 2:14: "When the Gentiles, who have not the law, do by nature those things that are of the law," comments as follows: "Although they have no written law, yet they have the natural law, whereby each one knows, and is conscious of, what is good and what is evil."

  I answer that, As stated above (Question [90], Article [1], ad 1), law, being a rule and measure, can be in a person in two ways: in one way, as in him that rules and measures; in another way, as in that which is ruled and measured, since a thing is ruled and measured, in so far as it partakes of the rule or measure. Wherefore, since all things subject to Divine providence are ruled and measured by the eternal law, as was stated above (Article [1]); it is evident that all things partake somewhat of the eternal law, in so far as, namely, from its being imprinted on them, they derive their respective inclinations to their proper acts and ends. Now among all others, the rational creature is subject to Divine providence in the most excellent way, in so far as it partakes of a share of providence, by being provident both for itself and for others. Wherefore it has a share of the Eternal Reason, whereby it has a natural inclination to its proper act and end: and this participation of the eternal law in the rational creature is called the natural law. Hence the Psalmist after saying (Ps. 4:6): "Offer up the sacrifice of justice," as though someone asked what the works of justice are, adds: "Many say, Who showeth us good things?" in answer to which question he says: "The light of Thy countenance, O Lord, is signed upon us": thus implying that the light of natural reason, whereby we discern what is good and what is evil, which is the function of the natural law, is nothing else than an imprint on us of the Divine light. It is therefore evident that the natural law is nothing else than the rational creature's participation of the eternal law. (Replies deleted.)


Article 3: Whether there is a human law?

  Objection 1: It would seem that there is not a human law. For the natural law is a participation of the eternal law, as stated above (Article [2]). Now through the eternal law "all things are most orderly," as Augustine states (De Lib. Arb. i, 6). Therefore the natural law suffices for the ordering of all human affairs. Consequently there is no need for a human law.

  Objection 2: Further, a law bears the character of a measure, as stated above (Question [90], Article [1]). But human reason is not a measure of things, but vice versa, as stated in Metaph. x, text. 5. Therefore no law can emanate from human reason.

  Objection 3: Further, a measure should be most certain, as stated in Metaph. x, text. 3. But the dictates of human reason in matters of conduct are uncertain, according to Wis. 9:14: "The thoughts of mortal men are fearful, and our counsels uncertain." Therefore no law can emanate from human reason.

  On the contrary, Augustine (De Lib. Arb. i, 6) distinguishes two kinds of law, the one eternal, the other temporal, which he calls human.

  I answer that, As stated above (Question [90], Article [1], ad 2), a law is a dictate of the practical reason. Now it is to be observed that the same procedure takes place in the practical and in the speculative reason: for each proceeds from principles to conclusions, as stated above (De Lib. Arb. i, 6). Accordingly we conclude that just as, in the speculative reason, from naturally known indemonstrable principles, we draw the conclusions of the various sciences, the knowledge of which is not imparted to us by nature, but acquired by the efforts of reason, so too it is from the precepts of the natural law, as from general and indemonstrable principles, that the human reason needs to proceed to the more particular determination of certain matters. These particular determinations, devised by human reason, are called human laws, provided the other essential conditions of law be observed, as stated above (Question [90], Articles [2],3,4). Wherefore Tully says in his Rhetoric (De Invent. Rhet. ii) that "justice has its source in nature; thence certain things came into custom by reason of their utility; afterwards these things which emanated from nature and were approved by custom, were sanctioned by fear and reverence for the law." (Replies deleted.)

Article 4: Whether there was any need for a Divine law? (excerpt)


  On the contrary, David prayed God to set His law before him, saying (Ps. 118:33): "Set before me for a law the way of Thy justifications, O Lord."

  I answer that, Besides the natural and the human law it was necessary for the directing of human conduct to have a Divine law. And this for four reasons. First, because it is by law that man is directed how to perform his proper acts in view of his last end. And indeed if man were ordained to no other end than that which is proportionate to his natural faculty, there would be no need for man to have any further direction of the part of his reason, besides the natural law and human law which is derived from it. But since man is ordained to an end of eternal happiness which is inproportionate to man's natural faculty, as stated above (Question [5], Article [5]), therefore it was necessary that, besides the natural and the human law, man should be directed to his end by a law given by God.