Is Isidore’s division of human laws appropriate?

It seems that Isidore proposes an inappropriate division of human statutes or human law:

Objection 1:  Under human law (ius) he includes the law of nations (ius gentium), which, as he explains, is so‑called because nearly all the nations make use of it.  But as he himself says, the natural law is common to all nations.  Therefore, the law of nations is contained under natural law rather than under positive human law.

Objection 2:  Things that have the same force seem to differ from one another only materially and not formally.  But statutes (leges), popular ordinances (plebiscita), senate decrees (senatusconsulta), etc., all seem to have the same force.  Therefore, it seems that they differ from one another only materially.  But a theory (ars) should not bother with this sort of distinction, since it could go on ad infinitum.  Therefore, it is inappropriate to make this sort of division of human laws.

Objection 3:  Just as a city has rulers and priests and soldiers, so too there are other roles men play as well.  Therefore, it seems that just as one posits military law (ius militare) along with public law (ius publicum), which covers priests and magistrates, so too one should posit other types of law that correspond to other roles in the community.

Objection 4:  What is per accidens should be left out of consideration.  But it is incidental to law that it is made by this or that man.  Therefore, it is inappropriate to posit a divisions of human laws by reference to the names of lawmakers, as for example to call one sort of law Cornelian law and another sort Falcidian law, etc.

But contrary to this:  The authority of Isidore is sufficient here.

I respond:  Each thing is divisible per se on the basis of what is contained in its definition (ratio).  For instance, soul, which is either rational or non‑rational, is contained in the definition of animal, and so animal is divided properly and per se by rational and non‑rational.  By contrast, animal is not properly and per se divided by white and black, which lie completely outside of the definition of animal.
Now there are many elements in the definition of human law, and human law can be properly and per se divided in accordance with each of them.
First of all, as was explained above (a. 2), it is part of the definition of human law that human law stems from the law of nature.  Accordingly, positive law (ius positivum) is divided into the law of nations (ius gentium) and civil law (ius civile), in keeping with the two modes, explained above (a. 2), in which something stems from the law of nature.  For things that belong to the law of nations stem from the law of nature as conclusions from principles—e.g., justice in buying and selling, etc., in the absence of which men would be unable to live together with one another.   This belongs to the natural law, since as Politics 1 shows, man is by nature a social animal.  On the other hand, things that stem from the law of nature in the manner of particular specifications belong to civil law, according to which each community determines what is fitting for itself.
Second, it is part of the definition of human law that human law is ordered toward the common good of the community.  Accordingly, human law can be divided by the diversity of roles played by those who work specifically for the common good—e.g., priests, who pray to God on behalf of the people; rulers, who govern the people; and soldiers, who fight for the safety of the people.  And so special laws are adapted to these men as such.
Third, as was explained above (q. 90, a. 3), it is part of the definition of human law that human is instituted by one who governs the civil community.  Accordingly, human laws are divided by the diverse forms of civil government (regimina).  One of these forms, according to the Philosopher in Politics 3, is the kingdom (regnum), viz., when the community is governed by one man, and, accordingly, this regime gives rise to the Princely Constitutions.  Another form of government is the aristocracy, i.e., rule by the best or by the party of the best (optimates), and, accordingly, this regime gives rise to the Counsels of the Wise (Responsa Prudentum) and also the Senate Decrees (Senatusconsulta).  The next form of government is the oligarchy, i.e., rule by a few rich and powerful men, and, accordingly, this regime gives rise to the Praetorian Law (Ius Praetorium), which is also called the Law of Honor (Ius Honararium).  Another form of government is government by the people, which goes by the name democrary, and, accordingly, this regime gives rise to Popular Ordinances (plebiscita).  The last form of government is tyranny, which is altogether corrupt and hence it does not give rise to any sort of law.  There is also a mixed form of government—the best form—and, accordingly, this regime gives rise to a type of law which, as Isidore puts it, has been sanctioned by the elders along with the common people.
Fourth, it is part of the definition of human law that it directs human acts.  Accordingly, laws are divided by the diverse acts about which laws are made.  Sometimes these laws are named after their authors, e.g., the Julian law concerns acts of adultery, the Cornelian law concerns assassination, and so on—the laws are distinguished in this way not because of their authors, but because of the deeds the acts they are concerned with.

Reply to objection 1:  The law of nations is, to be sure, in some sense natural to man insofar as he is rational, since it stems from the natural law in the manner of a conclusion that is not very far removed from its principles.  Hence, it was easy for men to agree to a law of this sort.  However, the law of nations is nonetheless distinct from the natural law, especially from what is common to all animals.

Reply to objection 2 and objection 3 and objection 4:  The replies to the other objections are clear from what has been said.