Summa Th. I-II EN Qu.100 a.6
Objection: 1. It would seem that the ten precepts of the decalogue are not set in proper order. Because love of one's neighbor is seemingly previous to love of God, since our neighbor is better known to us than God is; according to 1Jn 4,20: "He that loveth not his brother, whom he seeth, how can he love God, Whom he seeth not?" But the first three precepts belong to the love of God, while the other seven pertain to the love of our neighbor. Therefore the precepts of the decalogue are not set in proper order.
2. Further, the acts of virtue are prescribed by the affirmative precepts, and acts of vice are forbidden by the negative precepts. But according to Boethius in his commentary on the Categories [*Lib. iv, cap. De Oppos.], vices should be uprooted before virtues are sown. Therefore among the precepts concerning our neighbor, the negative precepts should have preceded the affirmative.
3. Further, the precepts of the Law are about men's actions. But actions of thought precede actions of word or outward deed. Therefore the precepts about not coveting, which regard our thoughts, are unsuitably placed last in order.
On the contrary The Apostle says (Rm 13,1): "The things that are of God, are well ordered" [Vulg.: 'Those that are, are ordained of God']. But the precepts of the decalogue were given immediately by God, as stated above (Article ). Therefore they are arranged in becoming order.
I answer that As stated above (Articles ,5, ad 1), the precepts of the decalogue are such as the mind of man is ready to grasp at once. Now it is evident that a thing is so much the more easily grasped by the reason, as its contrary is more grievous and repugnant to reason. Moreover, it is clear, since the order of reason begins with the end, that, for a man to be inordinately disposed towards his end, is supremely contrary to reason. Now the end of human life and society is God. Consequently it was necessary for the precepts of the decalogue, first of all, to direct man to God; since the contrary to this is most grievous. Thus also, in an army, which is ordained to the commander as to its end, it is requisite first that the soldier should be subject to the commander, and the opposite of this is most grievous; and secondly it is requisite that he should be in coordination with the other soldiers.Now among those things whereby we are ordained to God, the first is that man should be subjected to Him faithfully, by having nothing in common with His enemies. The second is that he should show Him reverence: the third that he should offer Him service. Thus, in an army, it is a greater sin for a soldier to act treacherously and make a compact with the foe, than to be insolent to his commander: and this last is more grievous than if he be found wanting in some point of service to him.As to the precepts that direct man in his behavior towards his neighbor, it is evident that it is more repugnant to reason, and a more grievous sin, if man does not observe the due order as to those persons to whom he is most indebted. Consequently, among those precepts that direct man in his relations to his neighbor, the first place is given to that one which regards his parents. Among the other precepts we again find the order to be according to the gravity of sin. For it is more grave and more repugnant to reason, to sin by deed than by word; and by word than by thought. And among sins of deed, murder which destroys life in one already living is more grievous than adultery, which imperils the life of the unborn child; and adultery is more grave than theft, which regards external goods.
Reply to Objection: 1. Although our neighbor is better known than God by the way of the senses, nevertheless the love of God is the reason for the love of our neighbor, as shall be declared later on (II-II 25,1; II-II 26,2). Hence the precepts ordaining man to God demanded precedence of the others.
2. Just as God is the universal principle of being in respect of all things, so is a father a principle of being in respect of his son. Therefore the precept regarding parents was fittingly placed after the precepts regarding God. This argument holds in respect of affirmative and negative precepts about the same kind of deed: although even then it is not altogether cogent. For although in the order of execution, vices should be uprooted before virtues are sown, according to Ps 33,15: "Turn away from evil, and do good," and Is 1,16-17: "Cease to do perversely; learn to do well"; yet, in the order of knowledge, virtue precedes vice, because "the crooked line is known by the straight" (De Anima i): and "by the law is the knowledge of sin" (Rm 3,20). Wherefore the affirmation precept demanded the first place. However, this is not the reason for the order, but that which is given above. Because in the precepts regarding God, which belongs to the first table, an affirmative precept is placed last, since its transgression implies a less grievous sin.
3. Although sin of thought stands first in the order of execution, yet its prohibition holds a later position in the order of reason.
Objection: 1. It would seem that the precepts of the decalogue are unsuitably formulated. Because the affirmative precepts direct man to acts of virtue, while the negative precepts withdraw him from acts of vice. But in every matter there are virtues and vices opposed to one another. Therefore in whatever matter there is an ordinance of a precept of the decalogue, there should have been an affirmative and a negative precept. Therefore it was unfitting that affirmative precepts should be framed in some matters, and negative precepts in others.
2. Further, Isidore says (Etym. ii, 10) that every law is based on reason. But all the precepts of the decalogue belong to the Divine law. Therefore the reason should have been pointed out in each precept, and not only in the first and third.
3. Further, by observing the precepts man deserves to be rewarded by God. But the Divine promises concern the rewards of the precepts. Therefore the promise should have been included in each precept, and not only in the second and fourth.
4. Further, the Old Law is called "the law of fear," in so far as it induced men to observe the precepts, by means of the threat of punishments. But all the precepts of the decalogue belong to the Old Law. Therefore a threat of punishment should have been included in each, and not only in the first and second.
5. Further, all the commandments of God should be retained in the memory: for it is written (Pr 3,3): "Write them in the tables of thy heart." Therefore it was not fitting that mention of the memory should be made in the third commandment only. Consequently it seems that the precepts of the decalogue are unsuitably formulated.
On the contrary It is written (Sg 11,21) that "God made all things, in measure, number and weight." Much more therefore did He observe a suitable manner in formulating His Law.
I answer that The highest wisdom is contained in the precepts of the Divine law: wherefore it is written (Dt 4,6): "This is your wisdom and understanding in the sight of nations." Now it belongs to wisdom to arrange all things in due manner and order. Therefore it must be evident that the precepts of the Law are suitably set forth.
Reply to Objection: 1. Affirmation of one thing always leads to the denial of its opposite: but the denial of one opposite does not always lead to the affirmation of the other. For it follows that if a thing is white, it is not black: but it does not follow that if it is not black, it is white: because negation extends further than affirmation. And hence too, that one ought not to do harm to another, which pertains to the negative precepts, extends to more persons, as a primary dictate of reason, than that one ought to do someone a service or kindness. Nevertheless it is a primary dictate of reason that man is a debtor in the point of rendering a service or kindness to those from whom he has received kindness, if he has not yet repaid the debt. Now there are two whose favors no man can sufficiently repay, viz. God and man's father, as stated in Ethic. viii, 14. Therefore it is that there are only two affirmative precepts; one about the honor due to parents, the other about the celebration of the Sabbath in memory of the Divine favor.
2. The reasons for the purely moral precepts are manifest; hence there was no need to add the reason. But some of the precepts include ceremonial matter, or a determination of a general moral precept; thus the first precept includes the determination, "Thou shalt not make a graven thing"; and in the third precept the Sabbath-day is fixed. Consequently there was need to state the reason in each case.
3. Generally speaking, men direct their actions to some point of utility. Consequently in those precepts in which it seemed that there would be no useful result, or that some utility might be hindered, it was necessary to add a promise of reward. And since parents are already on the way to depart from us, no benefit is expected from them: wherefore a promise of reward is added to the precept about honoring one's parents. The same applies to the precept forbidding idolatry: since thereby it seemed that men were hindered from receiving the apparent benefit which they think they can get by entering into a compact with the demons.
4. Punishments are necessary against those who are prone to evil, as stated in Ethic. x, 9. Wherefore a threat of punishment is only affixed to those precepts of the law which forbade evils to which men were prone. Now men were prone to idolatry by reason of the general custom of the nations. Likewise men are prone to perjury on account of the frequent use of oaths. Hence it is that a threat is affixed to the first two precepts.
5. The commandment about the Sabbath was made in memory of a past blessing. Wherefore special mention of the memory is made therein. Or again, the commandment about the Sabbath has a determination affixed to it that does not belong to the natural law, wherefore this precept needed a special admonition.
Objection: 1. It would seem that the precepts of the decalogue are dispensable. For the precepts of the decalogue belong to the natural law. But the natural law fails in some cases and is changeable, like human nature, as the Philosopher says (Ethic. v, 7). Now the failure of law to apply in certain particular cases is a reason for dispensation, as stated above (Question , Article ; Question , Article ). Therefore a dispensation can be granted in the precepts of the decalogue.
2. Further, man stands in the same relation to human law as God does to Divine law. But man can dispense with the precepts of a law made by man. Therefore, since the precepts of the decalogue are ordained by God, it seems that God can dispense with them. Now our superiors are God's viceregents on earth; for the Apostle says (2Co 2,10): "For what I have pardoned, if I have pardoned anything, for your sakes have I done it in the person of Christ." Therefore superiors can dispense with the precepts of the decalogue.
3. Further, among the precepts of the decalogue is one forbidding murder. But it seems that a dispensation is given by men in this precept: for instance, when according to the prescription of human law, such as evil-doers or enemies are lawfully slain. Therefore the precepts of the decalogue are dispensable.
4. Further, the observance of the Sabbath is ordained by a precept of the decalogue. But a dispensation was granted in this precept; for it is written (1M 2,41): "And they determined in that day, saying: Whosoever shall come up to fight against us on the Sabbath-day, we will fight against him." Therefore the precepts of the decalogue are dispensable.
On the contrary are the words of Is 24,5, where some are reproved for that "they have changed the ordinance, they have broken the everlasting covenant"; which, seemingly, apply principally to the precepts of the decalogue. Therefore the precepts of the decalogue cannot be changed by dispensation.
I answer that As stated above (Question , Article ; Question , Article ), precepts admit of dispensation, when there occurs a particular case in which, if the letter of the law be observed, the intention of the lawgiver is frustrated. Now the intention of every lawgiver is directed first and chiefly to the common good; secondly, to the order of justice and virtue, whereby the common good is preserved and attained. If therefore there by any precepts which contain the very preservation of the common good, or the very order of justice and virtue, such precepts contain the intention of the lawgiver, and therefore are indispensable. For instance, if in some community a law were enacted, such as this---that no man should work for the destruction of the commonwealth, or betray the state to its enemies, or that no man should do anything unjust or evil, such precepts would not admit of dispensation. But if other precepts were enacted, subordinate to the above, and determining certain special modes of procedure, these latter precepts would admit of dispensation, in so far as the omission of these precepts in certain cases would not be prejudicial to the former precepts which contain the intention of the lawgiver. For instance if, for the safeguarding of the commonwealth, it were enacted in some city that from each ward some men should keep watch as sentries in case of siege, some might be dispensed from this on account of some greater utility.Now the precepts of the decalogue contain the very intention of the lawgiver, who is God. For the precepts of the first table, which direct us to God, contain the very order to the common and final good, which is God; while the precepts of the second table contain the order of justice to be observed among men, that nothing undue be done to anyone, and that each one be given his due; for it is in this sense that we are to take the precepts of the decalogue. Consequently the precepts of the decalogue admit of no dispensation whatever.
Reply to Objection: 1. The Philosopher is not speaking of the natural law which contains the very order of justice: for it is a never-failing principle that "justice should be preserved." But he is speaking in reference to certain fixed modes of observing justice, which fail to apply in certain cases.
2. As the Apostle says (2Tm 2,13), "God continueth faithful, He cannot deny Himself." But He would deny Himself if He were to do away with the very order of His own justice, since He is justice itself. Wherefore God cannot dispense a man so that it be lawful for him not to direct himself to God, or not to be subject to His justice, even in those matters in which men are directed to one another.
3. The slaying of a man is forbidden in the decalogue, in so far as it bears the character of something undue: for in this sense the precept contains the very essence of justice. Human law cannot make it lawful for a man to be slain unduly. But it is not undue for evil-doers or foes of the common weal to be slain: hence this is not contrary to the precept of the decalogue; and such a killing is no murder as forbidden by that precept, as Augustine observes (De Lib. Arb. i, 4). In like manner when a man's property is taken from him, if it be due that he should lose it, this is not theft or robbery as forbidden by the decalogue.Consequently when the children of Israel, by God's command, took away the spoils of the Egyptians, this was not theft; since it was due to them by the sentence of God. Likewise when Abraham consented to slay his son, he did not consent to murder, because his son was due to be slain by the command of God, Who is Lord of life and death: for He it is Who inflicts the punishment of death on all men, both godly and ungodly, on account of the sin of our first parent, and if a man be the executor of that sentence by Divine authority, he will be no murderer any more than God would be. Again Osee, by taking unto himself a wife of fornications, or an adulterous woman, was not guilty either of adultery or of fornication: because he took unto himself one who was his by command of God, Who is the Author of the institution of marriage.Accordingly, therefore, the precepts of the decalogue, as to the essence of justice which they contain, are unchangeable: but as to any determination by application to individual actions---for instance, that this or that be murder, theft or adultery, or not---in this point they admit of change; sometimes by Divine authority alone, namely, in such matters as are exclusively of Divine institution, as marriage and the like; sometimes also by human authority, namely in such matters as are subject to human jurisdiction: for in this respect men stand in the place of God: and yet not in all respects.
4. This determination was an interpretation rather than a dispensation. For a man is not taken to break the Sabbath, if he does something necessary for human welfare; as Our Lord proves (Mt 12,3, seqq.).
Objection: 1. It would seem that the mode of virtue falls under the precept of the law. For the mode of virtue is that deeds of justice should be done justly, that deeds of fortitude should be done bravely, and in like manner as to the other virtues. But it is commanded (Dt 26,20) that "thou shalt follow justly after that which is just." Therefore the mode of virtue falls under the precept.
2. Further, that which belongs to the intention of the lawgiver comes chiefly under the precept. But the intention of the lawgiver is directed chiefly to make men virtuous, as stated in Ethic. ii: and it belongs to a virtuous man to act virtuously. Therefore the mode of virtue falls under the precept.
3. Further, the mode of virtue seems to consist properly in working willingly and with pleasure. But this falls under a precept of the Divine law, for it is written (Ps 99,2): "Serve ye the Lord with gladness"; and (2Co 9,7): "Not with sadness or necessity: for God loveth a cheerful giver"; whereupon the gloss says: "Whatever ye do, do gladly; and then you will do it well; whereas if you do it sorrowfully, it is done in thee, not by thee." Therefore the mode of virtue falls under the precept of the law.
On the contrary No man can act as a virtuous man acts unless he has the habit of virtue, as the Philosopher explains (Ethic. ii, 4; v, 8). Now whoever transgresses a precept of the law, deserves to be punished. Hence it would follow that a man who has not the habit of virtue, would deserve to be punished, whatever he does. But this is contrary to the intention of the law, which aims at leading man to virtue, by habituating him to good works. Therefore the mode of virtue does not fall under the precept.
I answer that As stated above (Question , Article , ad 2), a precept of law has compulsory power. Hence that on which the compulsion of the law is brought to bear, falls directly under the precept of the law. Now the law compels through fear of punishment, as stated in Ethic. x, 9, because that properly falls under the precept of the law, for which the penalty of the law is inflicted. But Divine law and human law are differently situated as to the appointment of penalties; since the penalty of the law is inflicted only for those things which come under the judgment of the lawgiver; for the law punishes in accordance with the verdict given. Now man, the framer of human law, is competent to judge only of outward acts; because "man seeth those things that appear," according to 1S 16,7: while God alone, the framer of the Divine law, is competent to judge of the inward movements of wills, according to Ps 7,10: "The searcher of hearts and reins is God."Accordingly, therefore, we must say that the mode of virtue is in some sort regarded both by human and by Divine law; in some respect it is regarded by the Divine, but not by the human law; and in another way, it is regarded neither by the human nor by the Divine law. Now the mode of virtue consists in three things, as the Philosopher states in Ethic. ii. The first is that man should act "knowingly": and this is subject to the judgment of both Divine and human law; because what a man does in ignorance, he does accidentally. Hence according to both human and Divine law, certain things are judged in respect of ignorance to be punishable or pardonable.The second point is that a man should act "deliberately," i.e. "from choice, choosing that particular action for its own sake"; wherein a twofold internal movement is implied, of volition and of intention, about which we have spoken above (Questions , 12): and concerning these two, Divine law alone, and not human law, is competent to judge. For human law does not punish the man who wishes to slay, and slays not: whereas the Divine law does, according to Mt 5,22: "Whosoever is angry with his brother, shall be in danger of the judgment."The third point is that he should "act from a firm and immovable principle": which firmness belongs properly to a habit, and implies that the action proceeds from a rooted habit. In this respect, the mode of virtue does not fall under the precept either of Divine or of human law, since neither by man nor by God is he punished as breaking the law, who gives due honor to his parents and yet has not the habit of filial piety.
Reply to Objection: 1. The mode of doing acts of justice, which falls under the precept, is that they be done in accordance with right; but not that they be done from the habit of justice.
2. The intention of the lawgiver is twofold. His aim, in the first place, is to lead men to something by the precepts of the law: and this is virtue. Secondly, his intention is brought to bear on the matter itself of the precept: and this is something leading or disposing to virtue, viz. an act of virtue. For the end of the precept and the matter of the precept are not the same: just as neither in other things is the end the same as that which conduces to the end.
3. That works of virtue should be done without sadness, falls under the precept of the Divine law; for whoever works with sadness works unwillingly. But to work with pleasure, i.e. joyfully or cheerfully, in one respect falls under the precept, viz. in so far as pleasure ensues from the love of God and one's neighbor (which love falls under the precept), and love causes pleasure: and in another respect does not fall under the precept, in so far as pleasure ensues from a habit; for "pleasure taken in a work proves the existence of a habit," as stated in Ethic. ii, 3. For an act may give pleasure either on account of its end, or through its proceeding from a becoming habit.
Objection: 1. It would seem that the mode of charity falls under the precept of the Divine law. For it is written (Mt 19,17): "If thou wilt enter into life, keep the commandments": whence it seems to follow that the observance of the commandments suffices for entrance into life. But good works do not suffice for entrance into life, except they be done from charity: for it is written (1Co 13,3): "If I should distribute all my goods to feed the poor, and if I should deliver my body to be burned, and have not charity, it profiteth me nothing." Therefore the mode of charity is included in the commandment.
2. Further, the mode of charity consists properly speaking in doing all things for God. But this falls under the precept; for the Apostle says (1Co 10,31): "Do all to the glory of God." Therefore the mode of charity falls under the precept.
3. Further, if the mode of charity does not fall under the precept, it follows that one can fulfil the precepts of the law without having charity. Now what can be done without charity can be done without grace, which is always united to charity. Therefore one can fulfil the precepts of the law without grace. But this is the error of Pelagius, as Augustine declares (De Haeres. lxxxviii). Therefore the mode of charity is included in the commandment.
On the contrary Whoever breaks a commandment sins mortally. If therefore the mode of charity falls under the precept, it follows that whoever acts otherwise than from charity sins mortally. But whoever has not charity, acts otherwise than from charity. Therefore it follows that whoever has not charity, sins mortally in whatever he does, however good this may be in itself: which is absurd.
I answer that Opinions have been contrary on this question. For some have said absolutely that the mode of charity comes under the precept; and yet that it is possible for one not having charity to fulfil this precept: because he can dispose himself to receive charity from God. Nor (say they) does it follow that a man not having charity sins mortally whenever he does something good of its kind: because it is an affirmative precept that binds one to act from charity, and is binding not for all time, but only for such time as one is in a state of charity. On the other hand, some have said that the mode of charity is altogether outside the precept.Both these opinions are true up to a certain point. Because the act of charity can be considered in two ways. First, as an act by itself: and thus it falls under the precept of the law which specially prescribes it, viz. "Thou shalt love the Lord thy God," and "Thou shalt love thy neighbor." In this sense, the first opinion is true. Because it is not impossible to observe this precept which regards the act of charity; since man can dispose himself to possess charity, and when he possesses it, he can use it. Secondly, the act of charity can be considered as being the mode of the acts of the other virtues, i.e. inasmuch as the acts of the other virtues are ordained to charity, which is "the end of the commandment," as stated in 1Tm 1,5: for it has been said above (Question , Article ) that the intention of the end is a formal mode of the act ordained to that end. In this sense the second opinion is true in saying that the mode of charity does not fall under the precept, that is to say that this commandment, "Honor thy father," does not mean that a man must honor his father from charity, but merely that he must honor him. Wherefore he that honors his father, yet has not charity, does not break this precept: although he does break the precept concerning the act of charity, for which reason he deserves to be punished.
Reply to Objection: 1. Our Lord did not say, "If thou wilt enter into life, keep one commandment"; but "keep" all "the commandments": among which is included the commandment concerning the love of God and our neighbor.
2. The precept of charity contains the injunction that God should be loved from our whole heart, which means that all things would be referred to God. Consequently man cannot fulfil the precept of charity, unless he also refer all things to God. Wherefore he that honors his father and mother, is bound to honor them from charity, not in virtue of the precept, "Honor thy father and mother," but in virtue of the precept, "Thou shalt love the Lord thy God with thy whole heart." And since these are two affirmative precepts, not binding for all times, they can be binding, each one at a different time: so that it may happen that a man fulfils the precept of honoring his father and mother, without at the same time breaking the precept concerning the omission of the mode of charity.
3. Man cannot fulfil all the precepts of the law, unless he fulfil the precept of charity, which is impossible without charity. Consequently it is not possible, as Pelagius maintained, for man to fulfil the law without grace.
Objection: 1. It would seem that it is wrong to distinguish other moral precepts of the law besides the decalogue. Because, as Our Lord declared (Mt 22,40), "on these two commandments" of charity "dependeth the whole law and the prophets." But these two commandments are explained by the ten commandments of the decalogue. Therefore there is no need for other moral precepts.
2. Further, the moral precepts are distinct from the judicial and ceremonial precepts, as stated above (Question , Articles ,4). But the determinations of the general moral precepts belong to the judicial and ceremonial precepts: and the general moral precepts are contained in the decalogue, or are even presupposed to the decalogue, as stated above (Article ). Therefore it was unsuitable to lay down other moral precepts besides the decalogue.
3. Further, the moral precepts are about the acts of all the virtues, as stated above (Article ). Therefore, as the Law contains, besides the decalogue, moral precepts pertaining to religion, liberality, mercy, and chastity; so there should have been added some precepts pertaining to the other virtues, for instance, fortitude, sobriety, and so forth. And yet such is not the case. It is therefore unbecoming to distinguish other moral precepts in the Law besides those of the decalogue.
On the contrary It is written (Ps 18,8): "The law of the Lord is unspotted, converting souls." But man is preserved from the stain of sin, and his soul is converted to God by other moral precepts besides those of the decalogue. Therefore it was right for the Law to include other moral precepts.
I answer that As is evident from what has been stated (Question , Articles ,4), the judicial and ceremonial precepts derive their force from their institution alone: since before they were instituted, it seemed of no consequence whether things were done in this or that way. But the moral precepts derive their efficacy from the very dictate of natural reason, even if they were never included in the Law. Now of these there are three grades: for some are most certain, and so evident as to need no promulgation; such as the commandments of the love of God and our neighbor, and others like these, as stated above (Article ), which are, as it were, the ends of the commandments; wherefore no man can have an erroneous judgment about them. Some precepts are more detailed, the reason of which even an uneducated man can easily grasp; and yet they need to be promulgated, because human judgment, in a few instances, happens to be led astray concerning them: these are the precepts of the decalogue. Again, there are some precepts the reason of which is not so evident to everyone, but only the wise; these are moral precepts added to the decalogue, and given to the people by God through Moses and Aaron.But since the things that are evident are the principles whereby we know those that are not evident, these other moral precepts added to the decalogue are reducible to the precepts of the decalogue, as so many corollaries. Thus the first commandment of the decalogue forbids the worship of strange gods: and to this are added other precepts forbidding things relating to worship of idols: thus it is written (Dt 18,10-11): "Neither let there be found among you anyone that shall expiate his son or daughter, making them to pass through the fire: . . . neither let there by any wizard nor charmer, nor anyone that consulteth pythonic spirits, or fortune-tellers, or that seeketh the truth from the dead." The second commandment forbids perjury. To this is added the prohibition of blasphemy (Lv 24,15, seqq) and the prohibition of false doctrine (Dt 13). To the third commandment are added all the ceremonial precepts. To the fourth commandment prescribing the honor due to parents, is added the precept about honoring the aged, according to Lv 19,32: "Rise up before the hoary head, and honor the person of the aged man"; and likewise all the precepts prescribing the reverence to be observed towards our betters, or kindliness towards our equals or inferiors. To the fifth commandment, which forbids murder, is added the prohibition of hatred and of any kind of violence inflicted on our neighbor, according to Lv 19,16: "Thou shalt not stand against the blood of thy neighbor": likewise the prohibition against hating one's brother (Lv 19,17): "Thou shalt not hate thy brother in thy heart." To the sixth commandment which forbids adultery, is added the prohibition about whoredom, according to Dt 23,17: "There shall be no whore among the daughters of Israel, nor whoremonger among the sons of Israel"; and the prohibition against unnatural sins, according to Lv 28,22-23: "Thou shalt not lie with mankind . . . thou shalt not copulate with any beast." To the seventh commandment which prohibits theft, is added the precept forbidding usury, according to Dt 23,19: "Thou shalt not lend to thy brother money to usury"; and the prohibition against fraud, according to Dt 25,13: "Thou shalt not have divers weights in thy bag"; and universally all prohibitions relating to peculations and larceny. To the eighth commandment, forbidding false testimony, is added the prohibition against false judgment, according to Ex 23,2: "Neither shalt thou yield in judgment, to the opinion of the most part, to stray from the truth"; and the prohibition against lying (Ex 23,7): "Thou shalt fly lying," and the prohibition against detraction, according to Lv 19,16: "Thou shalt not be a detractor, nor a whisperer among the people." To the other two commandments no further precepts are added, because thereby are forbidden all kinds of evil desires.
Reply to Objection: 1. The precepts of the decalogue are ordained to the love of God and our neighbor as pertaining evidently to our duty towards them; but the other precepts are so ordained as pertaining thereto less evidently.
2. It is in virtue of their institution that the ceremonial and judicial precepts "are determinations of the precepts of the decalogue," not by reason of a natural instinct, as in the case of the superadded moral precepts.
3. The precepts of a law are ordained for the common good, as stated above (Question , Article ). And since those virtues which direct our conduct towards others pertain directly to the common good, as also does the virtue of chastity, in so far as the generative act conduces to the common good of the species; hence precepts bearing directly on these virtues are given, both in the decalogue and in addition thereto. As to the act of fortitude there are the order to be given by the commanders in the war, which is undertaken for the common good: as is clear from Dt 20,3, where the priest is commanded (to speak thus): "Be not afraid, do not give back." In like manner the prohibition of acts of gluttony is left to paternal admonition, since it is contrary to the good of the household; hence it is said (Dt 21,20) in the person of parents: "He slighteth hearing our admonitions, he giveth himself to revelling, and to debauchery and banquetings."
Summa Th. I-II EN Qu.100 a.6