Is there an appropriate number of precepts in the Decalogue?

It seems that there is an inappropriate number of precepts in the Decalogue:

Objection 1:  As Ambrose says, “Sin is a transgression of divine law and disobedience against the heavenly commandments.”  But sins are distinguished from one another by whether a man sins against God, against his neighbor, or against himself.  Therefore, since among the precepts of the Decalogue there are none that order a man toward himself, but only ones that order him toward God and toward his neighbor, it seems that there is an insufficient number of precepts in the Decalogue.

Objection 2:  Just as the observance of the Sabbath had to do with the worship of God, so also did the observance of the other solemn feasts (solemnitates) and the immolation of sacrifices.  But among the precepts of the Decalogue there is a single precept having to do with the observance of the Sabbath.  Therefore, there should also be some precepts having to do with the other solemn feasts and with the rite of sacrifices.

Objection 3:  Just as one can sin against God by perjuring himself, so too he can sin against God by blasphemy or by various deceptions that are opposed to divine teaching.  But there is a single precept forbidding perjury, when it says, “You shall not take the name of the Lord your God in vain.”  Therefore, the sins of blasphemy and false teaching should be prohibited by some precept of the Decalogue.

Objection 4:  Just as a man has a natural love for his parents, so too he has a natural love for his children; indeed, the commandment of charity extends to all one’s neighbors.  But the precepts of the Decalogue are ordered toward charity—this according to 1 Timothy 1:5, “The end of the commandment is charity.”  Therefore, just as there is a precept having to do with one’s parents, so also there should have been precepts having to do with one’s children and other neighbors.

Objection 5:  In every genus of sin it is possible to sin with one’s heart and to sin with one’s deeds.  But within certain genera of sin, viz., in the case of theft and adultery, sinning by deed is prohibited in one place—viz., when it says, “You shall not commit adultery” and “You shall not steal”—and sinning with the heart is prohibited in a separate place—viz., when it says, “You shall not covet your neighbor’s good” and “You shall not covet your neighbor’s wife.”  Therefore, the same thing should have been done with the sin of homicide and the sin of false witness.

Objection 6:  Just as a sin can stem from a disorder of the concupiscible [appetite], so too a sin can stem from a disorder of the irascible [appetite].  But there are certain precepts prohibiting disordered desire, when it says, “Do not covet .....”  Therefore, the Decalogue should also have contained some precepts prohibiting a disordered irascible appetite.  Therefore, it does not seem that there is an appropriate number of precepts in the Decalogue.

But contrary to this:  Deuteronomy 4:13 says, “He showed you His covenant, which He commanded you to do, and the ten words that He wrote in the two tables of stone.”

I respond:  As was explained above (a. 2), just as the precepts of human law order a man toward the human community, so the precepts of divine law order a man toward a sort of community or republic of men under God.  Now in order for someone to live a good life in a community, two things are required.  The first is that he behave well toward the one who presides over the community, and the second is that the man behave well toward the others who are his companions and co‑participants in the community.  Therefore, divine law must first lay down some precepts ordering a man toward God and, second, it must lay down other precepts ordering a man toward those others who are living together with him as his neighbors under God.
Now there are three things a man owes to the ruler of his community:  (a) fidelity, (b) reverence, and (c) service (famulatus).  Fidelity to one’s lord consists in not conferring on someone else the honor of preeminence; and on this score there is the first precept, when it says, “You shall not have strange gods.”  Reverence to one’s lord requires that nothing injurious be done to him; and on this score there is the second precept, i.e., “You shall not take the name of the Lord your God in vain.”  Service is owed to a lord in repayment for the benefits his subjects receive from him; and here the relevant precept is the third, which has to do with the sanctification of the Sabbath in remembrance of the creation of things.
On the other hand, someone behaves well toward his neighbor both in a specific way and in a general way:
He behaves well in a specific way to the extent that he renders what he owes to those he is indebted to.  And on this score there is the precept that has to do with honoring one’s parents.
He behaves well in a general way, i.e., with respect to everyone, in that he inflicts no harm on anyone either by his deeds or with his mouth or with his heart.
As for deeds, in some cases harm is inflicted on one’s neighbor in his very person, i.e., with respect to his existence as a person; and this is prohibited when it says, “You shall not kill.”  Again, in some cases the harm is inflicted in a person joined to him in the propagation of offspring; and this is prohibited when it says, “You shall not commit adultery.”  And in some cases the harm is inflicted in his possessions, which are ordered to both him and those conjoined to him, and this is prohibited by saying, “You shall not steal.”
On the other hand, harm caused with the mouth is prohibited when it says, “You shall not bear false witness against your neighbor.”
And harm caused with the heart is prohibited when it says, “You shall not covet.”
Moreover, the three precepts ordered toward God could also be distinguished in accord with the specific differences by deed, with the mouth, and with the heart.  The first of these three percepts has to do with deeds, and thus it says there, “You shall not make graven images.”  The second precept has to do with the mouth, and thus it says, “You shall not take the name of your God in vain.”  The third precept has to do with the heart, since in the sanctification of the Sabbath, insofar as this is a moral precept, the stillness of the heart is directed toward God.
Alternatively, according to Augustine, through the first precept we revere the unity of the First Principle, through the second precept we revere God’s truth, and through the third precept we revere His goodness, by which we are sanctified and in which, as our end, we come to rest.

Reply to objection 1:  There are two possible replies to this objection.
First, the precepts of the Decalogue are traced back to the precept of love.  Now a precept had to be given to man concerning the love of God and neighbor, since in this regard the natural law had been obscured because of sin.  By contrast, this was not the case with respect to the love of self, because in this regard the natural law was still alive—or, alternatively, because the love of self is also included in the love of God and neighbor, since it is in ordering himself to God that a man has genuine love for himself.  And this is why the precepts of the Decalogue contains only precepts having to do one’s neighbor and with God.
The second possible reply is that the precepts of the Decalogue are the ones that the people received directly from God.  Hence, Deuteronomy 10:4 says, “He wrote in the tables, according as He had written before, the ten words, which the Lord spoke to you.”  Thus, the precepts of the Decalogue had to be such that they could be immediately understood by the people.  Now a precept has the character of something that is owed, and the fact that a man necessarily owes something to God or to his neighbor is easily grasped by a man—and especially by a man of faith (fidelis).  However, it not so readily apparent that a man is necessarily owed something in those matters that pertain to himself and not to another.  For at first glance it seems that everyone is free in matters that pertain to himself.  And so the precepts that prohibit a man’s disorders with respect to himself come to the people later on through the instruction of the wise.  Hence, they do not pertain to the Decalogue.

Reply to objection 2:  All the solemn feasts of the Old Testament were instituted in commemoration of some divine favor, either a past favor remembered or a future favor prefigured; and, likewise, it was for this reason that all the sacrifices were offered.  Now among all of God’s favors, the first and foremost is the favor of creation, which is commemorated in the sanctification of the Sabbath.  Hence, Exodus 20:11 gives the following as the reason for this precept:  “For in six days God made heaven and earth, etc.”  Moreover, among all the future favors that had to be prefigured, the principal and final one was rest in the mind of God, either in the present life through grace or in the future life through glory.  This was likewise prefigured by the Sabbath observance.  Hence, Isaiah 58:13 says, “If you turn away your foot from the Sabbath, from doing your own will in My holy day, and call the Sabbath delightful, and the holy of the Lord glorious ......”  For these are the favors that are first and foremost in the minds of men, especially men of faith.
By contrast, the other solemn feasts are celebrated because of certain particular favors that were temporally transitory.  Take, for instance, the celebration of the Passover because of the favor of the past liberation from Egypt and because of the future passion of Christ.  These events have passed in time, leading us into the rest of the spiritual Sabbath.  That is why, among the precepts of the Decalogue, mention was made only of the Sabbath, while all the other solemn feasts and sacrifices were left out.

Reply to objection 3:  As the Apostle says in Hebrews 6:16, “Men swear by one greater than themselves, and an oath for confirmation is the end of all their controversy.”  And so since oaths are common to everyone, the prohibition of disordered oaths is specifically made in a precept of the Decalogue.
By contrast, the sin of false teaching is relevant only to a few people, and hence it did not have to be mentioned among the precepts of the Decalogue.  (Still, according to some interpretations, the precept “You shall not take the name of your God in vain” does prohibit false teaching; for instance, one Gloss expounds [this precept] as follows:  “You shall not claim that Christ is a creature.”)

Reply to objection 4:  Natural reason directly dictates to a man that he should not inflict injury on anyone, and so the precept prohibiting harm extends to everyone.  However, natural reason does not directly dictate that a man should do something for another’s benefit, except in the case of someone to whom the man is indebted.  Now the debt a child owes to his father is so obvious that it cannot be denied by any sort of evasion.  For the father is a principle of generation and of esse and, afterwards, of upbringing and teaching.  And this is why it does not fall under a precept of the Decalogue that support or obedience should be given to anyone other than one’s parents.
On the other hand, parents do not seem to be indebted to their children because of any favors received from them; rather, just the opposite is the case.  Likewise, as the Philosopher puts it in Ethics 8, a child is a part of his father, and fathers love their children as a part of themselves.  Hence, the reason why there are no precepts in the Decalogue with regard to love of one’s children is the same as the reason why there are likewise no precepts that order a man toward himself.

Reply to objection 5:  The pleasure of adultery and the usefulness of riches are desirable for their own sake, insofar as they have the character of a pleasurable good or a useful good.  For this reason, what had to be prohibited in their case was not just the deed, but the desire (concupiscentia) as well.
By contrast, homicide (homicidium) and falsehood are horrific in their own right; for we naturally love our neighbor and love the truth, and they are not desired for the sake of anything else.  And so as far as the sins of homicide and false witness were concerned, it was necessary to prohibit only the deed and not the sin of the heart.

Reply to objection 6:  As was explained above (q. 25, a. 1), all of the irascible passions stem from the concupiscible passions.  And so in the precepts of the Decalogue, which are, as it were, the first elements of the Law, mention had to be made only of the concupiscible passions and not of the irascible passions.