Summa Th. I-II EN Qu.89 a.5
Objection: 1. It would seem that the first movements of the sensuality in unbelievers are mortal sins. For the Apostle says (Rm 8,1) that "there is . . . no condemnation to them that are in Christ Jesus, who walk not according to the flesh": and he is speaking there of the concupiscence of the sensuality, as appears from the context (Rm 7). Therefore the reason why concupiscence is not a matter of condemnation to those who walk not according to the flesh, i.e. by consenting to concupiscence, is because they are in Christ Jesus. But unbelievers are not in Christ Jesus. Therefore in unbelievers this is a matter of condemnation. Therefore the first movements of unbelievers are mortal sins.
2. Further Anselm says (De Gratia et Lib. Arb. vii): "Those who are not in Christ, when they feel the sting of the flesh, follow the road of damnation, even if they walk not according to the flesh." But damnation is not due save to mortal sin. Therefore, since man feels the sting of the flesh in the first movements of the concupiscence, it seems that the first movements of concupiscence in unbelievers are mortal sins.
3. Further, Anselm says (De Gratia et Lib. Arb. vii): "Man was so made that he was not liable to feel concupiscence." Now this liability seems to be remitted to man by the grace of Baptism, which the unbeliever has not. Therefore every act of concupiscence in an unbeliever, even without his consent, is a mortal sin, because he acts against his duty.
On the contrary It is stated in Ac 10,34 that "God is not a respecter of persons." Therefore he does not impute to one unto condemnation, what He does not impute to another. But he does not impute first movements to believers, unto condemnation. Neither therefore does He impute them to unbelievers.
I answer that It is unreasonable to say that the first movements of unbelievers are mortal sins, when they do not consent to them. This is evident for two reasons. First, because the sensuality itself could not be the subject of mortal sin, as stated above (Question , Article ). Now the sensuality has the same nature in unbelievers as in believers. Therefore it is not possible for the mere movements of the sensuality in unbelievers, to be mortal sins. Secondly, from the state of the sinner. Because excellence of the person of the person never diminishes sin, but, on the contrary, increases it, as stated above (Question , Article ). Therefore a sin is not less grievous in a believer than in an unbeliever, but much more so. For the sins of an unbeliever are more deserving of forgiveness, on account of their ignorance, according to 1Tm 1,13: "I obtained the mercy of God, because I did it ignorantly in my unbelief": whereas the sins of believers are more grievous on account of the sacraments of grace, according to He 10,29: "How much more, do you think, he deserveth worse punishments . . . who hath esteemed the blood of the testament unclean, by which he was sanctified?"
Reply to Objection: 1. The Apostle is speaking of the condemnation due to original sin, which condemnation is remitted by the grace of Jesus Christ, although the "fomes" of concupiscence remain. Wherefore the fact that believers are subject to concupiscence is not in them a sign of the condemnation due to original sin, as it is in unbelievers.
2. In this way also is to be understood the saying of Anselm, wherefore the Reply to the Second Objection is evident.
3. This freedom from liability to concupiscence was a result of original justice. Wherefore that which is opposed to such liability pertains, not to actual but to original sin.
Objection: 1. It would seem that venial sin can be in a man with original sin alone. For disposition precedes habit. Now venial sin is a disposition to mortal sin, as stated above (Question , Article ). Therefore in an unbeliever, in whom original sin is not remitted, venial sin exists before mortal sin: and so sometimes unbelievers have venial together with original sin, and without mortal sins.
2. Further, venial sin has less in common, and less connection with mortal sin, than one mortal sin has with another. But an unbeliever in the state of original sin, can commit one mortal sin without committing another. Therefore he can also commit a venial sin without committing a mortal sin.
3. Further, it is possible to fix the time at which a child is first able to commit an actual sin: and when the child comes to that time, it can stay a short time at least, without committing a mortal sin, because this happens in the worst criminals. Now it is possible for the child to sin venially during that space of time, however short it may be. Therefore venial sin can be in anyone with original sin alone and without mortal sin.
On the contrary Man is punished for original sin in the children's limbo, where there is no pain of sense as we shall state further on (II-II 69,6): whereas men are punished in hell for no other than mortal sin. Therefore there will be no place where a man can be punished for venial sin with no other than original sin.
I answer that It is impossible for venial sin to be in anyone with original sin alone, and without mortal sin. The reason for this is because before a man comes to the age of discretion, the lack of years hinders the use of reason and excuses him from mortal sin, wherefore, much more does it excuse him from venial sin, if he does anything which is such generically. But when he begins to have the use of reason, he is not entirely excused from the guilt of venial or mortal sin. Now the first thing that occurs to a man to think about then, is to deliberate about himself. And if he then direct himself to the due end, he will, by means of grace, receive the remission of original sin: whereas if he does not then direct himself to the due end, and as far as he is capable of discretion at that particular age, he will sin mortally, for through not doing that which is in his power to do. Accordingly thenceforward there cannot be venial sin in him without mortal, until afterwards all sin shall have been remitted to him through grace.
Reply to Objection: 1. Venial sin always precedes mortal sin not as a necessary, but as a contingent disposition, just as work sometimes disposes to fever, but not as heat disposes to the form of fire.
2. Venial sin is prevented from being with original sin alone, not on account of its want of connection or likeness, but on account of the lack of use of reason, as stated above.
3. The child that is beginning to have the use of reason can refrain from other mortal sins for a time, but it is not free from the aforesaid sin of omission, unless it turns to God as soon as possible. For the first thing that occurs to a man who has discretion, is to think of himself, and to direct other things to himself as to their end, since the end is the first thing in the intention. Therefore this is the time when man is bound by God's affirmative precept, which the Lord expressed by saying (Zach. 1:3): "Turn ye to Me . . . and I will turn to you."
TREATISE ON LAW (Questions 90-108)
We have now to consider the extrinsic principles of acts. Now the extrinsic principle inclining to evil is the devil, of whose temptations we have spoken in the I 114,0. But the extrinsic principle moving to good is God, Who both instructs us by means of His Law, and assists us by His Grace: wherefore in the first place we must speak of law; in the second place, of grace.
Concerning law, we must consider: (1) Law itself in general; (2) its parts. Concerning law in general three points offer themselves for our consideration: (1) Its essence; (2) The different kinds of law; (3) The effects of law.
Under the first head there are four points of inquiry:
(1) Whether law is something pertaining to reason?
(2) Concerning the end of law;
(3) Its cause;
(4) The promulgation of law.
Objection: 1. It would seem that law is not something pertaining to reason. For the Apostle says (Rm 7,23): "I see another law in my members," etc. But nothing pertaining to reason is in the members; since the reason does not make use of a bodily organ. Therefore law is not something pertaining to reason.
2. Further, in the reason there is nothing else but power, habit, and act. But law is not the power itself of reason. In like manner, neither is it a habit of reason: because the habits of reason are the intellectual virtues of which we have spoken above (Question ). Nor again is it an act of reason: because then law would cease, when the act of reason ceases, for instance, while we are asleep. Therefore law is nothing pertaining to reason.
3. Further, the law moves those who are subject to it to act aright. But it belongs properly to the will to move to act, as is evident from what has been said above (Question , Article ). Therefore law pertains, not to the reason, but to the will; according to the words of the Jurist (Lib. i, ff., De Const. Prin. leg. i): "Whatsoever pleaseth the sovereign, has force of law."
On the contrary It belongs to the law to command and to forbid. But it belongs to reason to command, as stated above (Question , Article ). Therefore law is something pertaining to reason.
I answer that Law is a rule and measure of acts, whereby man is induced to act or is restrained from acting: for "lex" [law] is derived from "ligare" [to bind], because it binds one to act. Now the rule and measure of human acts is the reason, which is the first principle of human acts, as is evident from what has been stated above (Question , Article , ad 3); since it belongs to the reason to direct to the end, which is the first principle in all matters of action, according to the Philosopher (Phys. ii). Now that which is the principle in any genus, is the rule and measure of that genus: for instance, unity in the genus of numbers, and the first movement in the genus of movements. Consequently it follows that law is something pertaining to reason.
Reply to Objection: 1. Since law is a kind of rule and measure, it may be in something in two ways. First, as in that which measures and rules: and since this is proper to reason, it follows that, in this way, law is in the reason alone. Secondly, as in that which is measured and ruled. In this way, law is in all those things that are inclined to something by reason of some law: so that any inclination arising from a law, may be called a law, not essentially but by participation as it were. And thus the inclination of the members to concupiscence is called "the law of the members."
2. Just as, in external action, we may consider the work and the work done, for instance the work of building and the house built; so in the acts of reason, we may consider the act itself of reason, i.e. to understand and to reason, and something produced by this act. With regard to the speculative reason, this is first of all the definition; secondly, the proposition; thirdly, the syllogism or argument. And since also the practical reason makes use of a syllogism in respect of the work to be done, as stated above (Question , Article ; Question , Article ) and since as the Philosopher teaches (Ethic. vii, 3); hence we find in the practical reason something that holds the same position in regard to operations, as, in the speculative intellect, the proposition holds in regard to conclusions. Such like universal propositions of the practical intellect that are directed to actions have the nature of law. And these propositions are sometimes under our actual consideration, while sometimes they are retained in the reason by means of a habit.
3. Reason has its power of moving from the will, as stated above (Question , Article ): for it is due to the fact that one wills the end, that the reason issues its commands as regards things ordained to the end. But in order that the volition of what is commanded may have the nature of law, it needs to be in accord with some rule of reason. And in this sense is to be understood the saying that the will of the sovereign has the force of law; otherwise the sovereign's will would savor of lawlessness rather than of law.
Objection: 1. It would seem that the law is not always directed to the common good as to its end. For it belongs to law to command and to forbid. But commands are directed to certain individual goods. Therefore the end of the law is not always the common good.
2. Further, the law directs man in his actions. But human actions are concerned with particular matters. Therefore the law is directed to some particular good.
3. Further, Isidore says (Etym. v, 3): "If the law is based on reason, whatever is based on reason will be a law." But reason is the foundation not only of what is ordained to the common good, but also of that which is directed private good. Therefore the law is not only directed to the good of all, but also to the private good of an individual.
On the contrary Isidore says (Etym. v, 21) that "laws are enacted for no private profit, but for the common benefit of the citizens."
I answer that As stated above (Article ), the law belongs to that which is a principle of human acts, because it is their rule and measure. Now as reason is a principle of human acts, so in reason itself there is something which is the principle in respect of all the rest: wherefore to this principle chiefly and mainly law must needs be referred. Now the first principle in practical matters, which are the object of the practical reason, is the last end: and the last end of human life is bliss or happiness, as stated above (Question , Article ; Question , Article ). Consequently the law must needs regard principally the relationship to happiness. Moreover, since every part is ordained to the whole, as imperfect to perfect; and since one man is a part of the perfect community, the law must needs regard properly the relationship to universal happiness. Wherefore the Philosopher, in the above definition of legal matters mentions both happiness and the body politic: for he says (Ethic. v, 1) that we call those legal matters "just, which are adapted to produce and preserve happiness and its parts for the body politic": since the state is a perfect community, as he says in Polit. i, 1.Now in every genus, that which belongs to it chiefly is the principle of the others, and the others belong to that genus in subordination to that thing: thus fire, which is chief among hot things, is the cause of heat in mixed bodies, and these are said to be hot in so far as they have a share of fire. Consequently, since the law is chiefly ordained to the common good, any other precept in regard to some individual work, must needs be devoid of the nature of a law, save in so far as it regards the common good. Therefore every law is ordained to the common good.
Reply to Objection: 1. A command denotes an application of a law to matters regulated by the law. Now the order to the common good, at which the law aims, is applicable to particular ends. And in this way commands are given even concerning particular matters.
2. Actions are indeed concerned with particular matters: but those particular matters are referable to the common good, not as to a common genus or species, but as to a common final cause, according as the common good is said to be the common end.
3. Just as nothing stands firm with regard to the speculative reason except that which is traced back to the first indemonstrable principles, so nothing stands firm with regard to the practical reason, unless it be directed to the last end which is the common good: and whatever stands to reason in this sense, has the nature of a law.
Objection: 1. It would seem that the reason of any man is competent to make laws. For the Apostle says (Rm 2,14) that "when the Gentiles, who have not the law, do by nature those things that are of the law . . . they are a law to themselves." Now he says this of all in general. Therefore anyone can make a law for himself.
2. Further, as the Philosopher says (Ethic. ii, 1), "the intention of the lawgiver is to lead men to virtue." But every man can lead another to virtue. Therefore the reason of any man is competent to make laws.
3. Further, just as the sovereign of a state governs the state, so every father of a family governs his household. But the sovereign of a state can make laws for the state. Therefore every father of a family can make laws for his household.
On the contrary Isidore says (Etym. v, 10): "A law is an ordinance of the people, whereby something is sanctioned by the Elders together with the Commonalty."
I answer that A law, properly speaking, regards first and foremost the order to the common good. Now to order anything to the common good, belongs either to the whole people, or to someone who is the viceregent of the whole people. And therefore the making of a law belongs either to the whole people or to a public personage who has care of the whole people: since in all other matters the directing of anything to the end concerns him to whom the end belongs.
Reply to Objection: 1. As stated above (Article , ad 1), a law is in a person not only as in one that rules, but also by participation as in one that is ruled. In the latter way each one is a law to himself, in so far as he shares the direction that he receives from one who rules him. Hence the same text goes on: "Who show the work of the law written in their hearts."
2. A private person cannot lead another to virtue efficaciously: for he can only advise, and if his advice be not taken, it has no coercive power, such as the law should have, in order to prove an efficacious inducement to virtue, as the Philosopher says (Ethic. x, 9). But this coercive power is vested in the whole people or in some public personage, to whom it belongs to inflict penalties, as we shall state further on (Question , Article , ad 3; II-II 64,3). Wherefore the framing of laws belongs to him alone.
3. As one man is a part of the household, so a household is a part of the state: and the state is a perfect community, according to Polit. i, 1. And therefore, as the good of one man is not the last end, but is ordained to the common good; so too the good of one household is ordained to the good of a single state, which is a perfect community. Consequently he that governs a family, can indeed make certain commands or ordinances, but not such as to have properly the force of law.
Objection: 1. It would seem that promulgation is not essential to a law. For the natural law above all has the character of law. But the natural law needs no promulgation. Therefore it is not essential to a law that it be promulgated.
2. Further, it belongs properly to a law to bind one to do or not to do something. But the obligation of fulfilling a law touches not only those in whose presence it is promulgated, but also others. Therefore promulgation is not essential to a law.
3. Further, the binding force of a law extends even to the future, since "laws are binding in matters of the future," as the jurists say (Cod. 1, tit. De lege et constit. leg. vii). But promulgation concerns those who are present. Therefore it is not essential to a law.
On the contrary It is laid down in the Decretals, dist. 4, that "laws are established when they are promulgated."
I answer that As stated above (Article ), a law is imposed on others by way of a rule and measure. Now a rule or measure is imposed by being applied to those who are to be ruled and measured by it. Wherefore, in order that a law obtain the binding force which is proper to a law, it must needs be applied to the men who have to be ruled by it. Such application is made by its being notified to them by promulgation. Wherefore promulgation is necessary for the law to obtain its force.Thus from the four preceding articles, the definition of law may be gathered; and it is nothing else than an ordinance of reason for the common good, made by him who has care of the community, and promulgated.
Reply to Objection: 1. The natural law is promulgated by the very fact that God instilled it into man's mind so as to be known by him naturally.
2. Those who are not present when a law is promulgated, are bound to observe the law, in so far as it is notified or can be notified to them by others, after it has been promulgated.
3. The promulgation that takes place now, extends to future time by reason of the durability of written characters, by which means it is continually promulgated. Hence Isidore says (Etym. v, 3; ii, 10) that "lex [law] is derived from legere [to read] because it is written."
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?
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.
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.
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 , Article , ad 2; Articles ,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 I 22,1 I 22,2, 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 Pr 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.
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.
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.
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.
2. Further, by the law man is directed, in his acts, to the end, as stated above (Question , Article ). 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.
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 , Article , 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 ); 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.
Reply to Objection: 1. This argument would hold, if the natural law were something different from the eternal law: whereas it is nothing but a participation thereof, as stated above.
2. Every act of reason and will in us is based on that which is according to nature, as stated above (Question , Article ): for every act of reasoning is based on principles that are known naturally, and every act of appetite in respect of the means is derived from the natural appetite in respect of the last end. Accordingly the first direction of our acts to their end must needs be in virtue of the natural law.
3. Even irrational animals partake in their own way of the Eternal Reason, just as the rational creature does. But because the rational creature partakes thereof in an intellectual and rational manner, therefore the participation of the eternal law in the rational creature is properly called a law, since a law is something pertaining to reason, as stated above (Question , Article ). Irrational creatures, however, do not partake thereof in a rational manner, wherefore there is no participation of the eternal law in them, except by way of similitude.
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 ). 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.
2. Further, a law bears the character of a measure, as stated above (Question , Article ). 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.
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 Sg 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 , Article , 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 , Articles ,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."
Reply to Objection: 1. The human reason cannot have a full participation of the dictate of the Divine Reason, but according to its own mode, and imperfectly. Consequently, as on the part of the speculative reason, by a natural participation of Divine Wisdom, there is in us the knowledge of certain general principles, but not proper knowledge of each single truth, such as that contained in the Divine Wisdom; so too, on the part of the practical reason, man has a natural participation of the eternal law, according to certain general principles, but not as regards the particular determinations of individual cases, which are, however, contained in the eternal law. Hence the need for human reason to proceed further to sanction them by law.
2. Human reason is not, of itself, the rule of things: but the principles impressed on it by nature, are general rules and measures of all things relating to human conduct, whereof the natural reason is the rule and measure, although it is not the measure of things that are from nature.
3. The practical reason is concerned with practical matters, which are singular and contingent: but not with necessary things, with which the speculative reason is concerned. Wherefore human laws cannot have that inerrancy that belongs to the demonstrated conclusions of sciences. Nor is it necessary for every measure to be altogether unerring and certain, but according as it is possible in its own particular genus.
Objection: 1. It would seem that there was no need for a Divine law. Because, as stated above (Article ), the natural law is a participation in us of the eternal law. But the eternal law is a Divine law, as stated above (Article ). Therefore there was no need for a Divine law in addition to the natural law, and human laws derived therefrom.
2. Further, it is written (Si 15,14) that "God left man in the hand of his own counsel." Now counsel is an act of reason, as stated above (Question , Article ). Therefore man was left to the direction of his reason. But a dictate of human reason is a human law as stated above (Article ). Therefore there is no need for man to be governed also by a Divine law.
3. Further, human nature is more self-sufficing than irrational creatures. But irrational creatures have no Divine law besides the natural inclination impressed on them. Much less, therefore, should the rational creature have a Divine law in addition to the natural law.
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 , Article ), 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.Secondly, because, on account of the uncertainty of human judgment, especially on contingent and particular matters, different people form different judgments on human acts; whence also different and contrary laws result. In order, therefore, that man may know without any doubt what he ought to do and what he ought to avoid, it was necessary for man to be directed in his proper acts by a law given by God, for it is certain that such a law cannot err.Thirdly, because man can make laws in those matters of which he is competent to judge. But man is not competent to judge of interior movements, that are hidden, but only of exterior acts which appear: and yet for the perfection of virtue it is necessary for man to conduct himself aright in both kinds of acts. Consequently human law could not sufficiently curb and direct interior acts; and it was necessary for this purpose that a Divine law should supervene.Fourthly, because, as Augustine says (De Lib. Arb. i, 5,6), human law cannot punish or forbid all evil deeds: since while aiming at doing away with all evils, it would do away with many good things, and would hinder the advance of the common good, which is necessary for human intercourse. In order, therefore, that no evil might remain unforbidden and unpunished, it was necessary for the Divine law to supervene, whereby all sins are forbidden.And these four causes are touched upon in Ps 118,8, where it is said: "The law of the Lord is unspotted," i.e. allowing no foulness of sin; "converting souls," because it directs not only exterior, but also interior acts; "the testimony of the Lord is faithful," because of the certainty of what is true and right; "giving wisdom to little ones," by directing man to an end supernatural and Divine.
Reply to Objection: 1. By the natural law the eternal law is participated proportionately to the capacity of human nature. But to his supernatural end man needs to be directed in a yet higher way. Hence the additional law given by God, whereby man shares more perfectly in the eternal law.
2. Counsel is a kind of inquiry: hence it must proceed from some principles. Nor is it enough for it to proceed from principles imparted by nature, which are the precepts of the natural law, for the reasons given above: but there is need for certain additional principles, namely, the precepts of the Divine law.
3. Irrational creatures are not ordained to an end higher than that which is proportionate to their natural powers: consequently the comparison fails.
Summa Th. I-II EN Qu.89 a.5