Is it correct to mark out moral precepts of the Law in addition to the Decalogue?

It seems incorrect to mark out (distinguere) moral precepts of the Law other than the Decalogue:

Objection 1:  As our Lord says in Matthew 22:40, “On these two precepts [of charity] depends the whole Law and the prophets.”  But these two precepts are explicated by the ten precepts of the Decalogue.  Therefore, it is unnecessary for there to be other moral precepts.

Objection 2:  As has been explained (q. 99, a. 3), the moral precepts are distinct from the judicial and ceremonial precepts.  But specifications of the general moral precepts are contained in the judicial and ceremonial precepts, whereas, as has been explained (a. 3), the general moral precepts themselves are contained in the ten precepts of the Decalogue—or are at least presupposed by the Decalogue.  Therefore, it is inappropriate for other moral precepts to be handed down in addition to the Decalogue.

Objection 3:  As was explained above (a. 2), the moral precepts are about the acts of all the virtues.  Therefore, just as, in addition to the Decalogue, the Law has moral precepts that deal with worship, generosity, mercy, and chastity, so too there should be precepts dealing with the other virtues, e.g., fortitude, sobriety, and others of this sort.  But such precepts are not to be found.  Therefore, it is incorrect to mark out in the Law other moral precepts that go beyond the Decalogue.

But contrary to this:  Psalm 18:8 says, “The law of the Lord is pure, converting souls.”  But there are other moral precepts, in addition to the Decalogue, through which a man is preserved without the stain of sin and through which his soul is converted.  Therefore, the Law had other moral precepts to hand down as well.

I respond:  As is clear from what was said above (q. 99, a. 3‑4), the judicial and ceremonial precepts have force solely by virtue of their being instituted, since before they were instituted, there was no apparent difference between things being done one way or another.  By contrast, the moral precepts would have had efficacy on the basis of the dictates of natural reason even if they had never been codified in the Law.
Now there are three levels (gradus) of moral precept:
(a) Some moral precepts are absolutely certain and so evident that they do not need to be made known publically (editione non indigent)—e.g., as was explained above (a. 3), the commandments about love of God and neighbor and others of this sort, which are, as it were, the ends of the precepts (fines praeceptorum) and so such that no one can make a mistaken judgment of reason about them.
(b) Other moral precepts are more specific (determinata) and such that anyone, even an ordinary man, can grasp the reason behind them (ratio) easily and immediately.  However, since human judgment about these precepts can be perverted in a few men, precepts of this sort need to be made known publically (indigent editione).  These precepts are the precepts of the Decalogue.
(c) Still other moral precepts are such that the reason behind them is not so evident to everyone; instead, it is evident only to the wise.  These precepts are the ones that were added to the Decalogue and given to the people by God through the mediation of Moses and Aaron.
Now since what is evident is the principle of cognition for what is not evident, these other moral precepts that were added to the Decalogue are traced back to the precepts of the Decalogue in the sense that they are a sort of addition to them.
For instance, the first precept of the Decalogue prohibits the worship of strange gods, and to this are added other precepts that prohibit things that are ordered toward the worship of idols—as, e.g., in Deuteronomy 18:10‑11:  “Do not let there be found among you anyone that shall purify his son or daughter by making them to pass through the fire ..... .  Neither let there be any evil magician or enchanter, or anyone who consults prophetic spirits, or fortune‑tellers, or who seeks truth from the dead.”
The second precept of the Decalogue prohibits perjury, and to this are added the prohibition of blasphemy in Leviticus 24:15 and the prohibition of false teaching in Deuteronomy 13.
To the third precept are added all the ceremonial precepts.
To the fourth precept, the one about honoring one’s parents, is added a precept about honoring the elderly—this according to Leviticus 19:32 (“Stand up in the presence of a hoary head, and honor the elderly person”)—and, more generally, all the precepts that induce one to show respect for one’s betters or give benefits to one’s equals or inferiors.
To the fifth precept, which prohibits homicide, are added the prohibition of hatred or any sort of injury (violatio) against one’s neighbor, as in Leviticus 19:16 (“You shall not stand against the blood of your neighbor”), and the prohibition of hatred of one’s brother, as in Leviticus 19:17 (“You shall not hate your brother in your heart”).
To the sixth precept, which prohibits adultery, are added the prohibition against prostitution (meretricium)—this according to Deuteronomy 23:17 (“There shall be no prostitutes among the daughters of Israel, nor fornicators among the sons of Israel”)—and, again, the prohibition of the vice against nature—this according to Leviticus 28:22-23 (“You shall not have sex with a male ..... You shall not copulate with any beast”).
To the seventh precept, which prohibits theft (furtum), are added the precept prohibiting usury (usura)—this according to Deuteronomy 23:19 (“You shalt not lend your brother money to usury”)—and the prohibition of fraud (fraus)—this according to Deuteronomy 25:13 (“You shall not have diverse weights in your bag”)—and, more generally, everything having to do with the prohibition of cheating (calumnia) and plundering (rapina).
To the eighth precept, which prohibits false witness, are added the prohibition of false judgment—this according to Exodus 23:2 (“You shall not acquiesce in judgment to the opinion of the majority, so as to stray from the truth”)—and the prohibition against lying, which is added in the same place (“You shall avoid lying”), and the prohibition against detraction—this according to Leviticus 19:16 (“You shall not be a detractor (criminator) or a whisperer among the people”).
However, no other precepts are added to the last two precepts of the Decalogue, since these precepts prohibit all evil desires in general.

Reply to objection 1:  The precepts of the Decalogue are ordered toward love of God and neighbor with the evident rationale of what is owed to them (secundum manifestam rationem debiti).  However, the additional precepts are ordered toward love of God and neighbor with a more hidden rationale.

Reply to objection 2:  The ceremonial and judicial precepts specify the precepts of the Decalogue by instituting something and not, as with the additional moral precepts, by the force of natural instinct.

Reply to objection 3:  As was explained above (q. 90, a. 2), the precepts of law are ordered toward the common good.  And it is because the virtues that order us to others are directly relevant to the common good—and, likewise, chastity, insofar as the act of generation subserves the common good—that both the precepts of the Decalogue and the additional precepts are given directly about these virtues.
By contrast, as far as the act of fortitude is concerned, the relevant precept has to be proposed by leaders giving exhortations in a war undertaken for the common good—as is clear from Deuteronomy 20:3, where the priest is commanded [to say], “Do not be afraid!  Do not yield!”
Similarly, the prohibition against gluttony is entrusted to paternal warnings, since gluttony is contrary to the good of the household (bonum domesticum).  Hence, Deuteronomy 21:20 says in the personage of the parents, “He hates listening to our admonitions; he is idle with his reveling and debauchery and socializing.”