of justice.

_On the contrary,_ Augustine says in _De Poenitentia_ [*De vera et
falsa Poenitentia, the authorship of which is unknown]: "Penance is
the vengeance of the sorrowful, ever punishing in them what they are
sorry for having done." But to take vengeance is an act of justice,
wherefore Tully says (De Inv. Rhet. ii) that one kind of justice is
called vindictive. Therefore it seems that penance is a species of
justice.

_I answer that,_ As stated above (A. 1, ad 2) penance is a special
virtue not merely because it sorrows for evil done (since charity
would suffice for that), but also because the penitent grieves for
the sin he has committed, inasmuch as it is an offense against God,
and purposes to amend. Now amendment for an offense committed against
anyone is not made by merely ceasing to offend, but it is necessary
to make some kind of compensation, which obtains in offenses
committed against another, just as retribution does, only that
compensation is on the part of the offender, as when he makes
satisfaction, whereas retribution is on the part of the person
offended against. Each of these belongs to the matter of justice,
because each is a kind of commutation. Wherefore it is evident that
penance, as a virtue, is a part of justice.

It must be observed, however, that according to the Philosopher
(Ethic. v, 6) a thing is said to be just in two ways, simply and
relatively. A thing is just simply when it is between equals, since
justice is a kind of equality, and he calls this the politic or
civil just, because all citizens are equal, in the point of being
immediately under the ruler, retaining their freedom. But a thing is
just relatively when it is between parties of whom one is subject to
the other, as a servant under his master, a son under his father, a
wife under her husband. It is this kind of just that we consider in
penance. Wherefore the penitent has recourse to God with a purpose
of amendment, as a servant to his master, according to Ps. 122:2:
"Behold, as the eyes of servants are on the hands of their
masters . . . so are our eyes unto the Lord our God, until He have
mercy on us"; and as a son to his father, according to Luke 15:21:
"Father, I have sinned against heaven and before thee"; and as a wife
to her husband, according to Jer. 3:1: "Thou hast prostituted thyself
to many lovers; nevertheless return to Me, saith the Lord."

Reply Obj. 1: As stated in _Ethic._ v, 1, justice is a virtue tow