e legal just,
i.e. positive law, into three parts. For some things are laid down
simply in a general way: and these are the general laws. Of these he
says that "the legal is that which originally was a matter of
indifference, but which, when enacted, is so no longer": as the
fixing of the ransom of a captive. Some things affect the community
in one respect, and individuals in another. These are called
"privileges," i.e. "private laws," as it were, because they regard
private persons, although their power extends to many matters; and in
regard to these, he adds, "and further, all particular acts of
legislation." Other matters are legal, not through being laws, but
through being applications of general laws to particular cases: such
are decrees which have the force of law; and in regard to these, he
adds "all matters subject to decrees."

Reply Obj. 2: A principle of direction should be applicable to many;
wherefore (Metaph. x, text. 4) the Philosopher says that all things
belonging to one genus, are measured by one, which is the principle
in that genus. For if there were as many rules or measures as there
are things measured or ruled, they would cease to be of use, since
their use consists in being applicable to many things. Hence law
would be of no use, if it did not extend further than to one single
act. Because the decrees of prudent men are made for the purpose of
directing individual actions; whereas law is a general precept, as
stated above (Q. 92, A. 2, Obj. 2).

Reply Obj. 3: "We must not seek the same degree of certainty in all
things" (Ethic. i, 3). Consequently in contingent matters, such as
natural and human things, it is enough for a thing to be certain, as
being true in the greater number of instances, though at times and
less frequently it fail.
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SECOND ARTICLE [I-II, Q. 96, Art. 2]

Whether It Belongs to the Human Law to Repress All Vices?

Objection 1: It would seem that it belongs to human law to repress
all vices. For Isidore says (Etym. v, 20) that "laws were made in
order that, in fear thereof, man's audacity might be held in check."
But it would not be held in check sufficiently, unless all evils were
repressed by law. Therefore human laws should repress all evils.

Obj. 2: Further, the intention of the lawgiver is to make the
citizens virtuous. But a man cannot be virtuous unless he forbear
from all kinds of vice. Therefore it belongs to human law to repress
all vi