ft. Voluntary commutations
are when a man voluntarily transfers his chattel to another person.
And if he transfer it simply so that the recipient incurs no debt, as
in the case of gifts, it is an act, not of justice but of liberality.
A voluntary transfer belongs to justice in so far as it includes the
notion of debt, and this may occur in many ways. First when one man
simply transfers his thing to another in exchange for another thing,
as happens in selling and buying. Secondly when a man transfers his
thing to another, that the latter may have the use of it with the
obligation of returning it to its owner. If he grant the use of a
thing gratuitously, it is called "usufruct" in things that bear
fruit; and simply "borrowing" on "loan" in things that bear no fruit,
such as money, pottery, etc.; but if not even the use is granted
gratis, it is called "letting" or "hiring." Thirdly, a man transfers
his thing with the intention of recovering it, not for the purpose of
its use, but that it may be kept safe, as in a "deposit," or under
some obligation, as when a man pledges his property, or when one man
stands security for another. In all these actions, whether voluntary
or involuntary, the mean is taken in the same way according to the
equality of repayment. Hence all these actions belong to the one same
species of justice, namely commutative justice. And this suffices for
the Replies to the Objections.
_______________________

FOURTH ARTICLE [II-II, Q. 61, Art. 4]

Whether the Just Is Absolutely the Same As Retaliation?

Objection 1: It would seem that the just is absolutely the same as
retaliation. For the judgment of God is absolutely just. Now the
judgment of God is such that a man has to suffer in proportion with
his deeds, according to Matt. 7:2: "With what measure you judge, you
shall be judged: and with what measure you mete, it shall be measured
to you again." Therefore the just is absolutely the same as
retaliation.

Obj. 2: Further, in either kind of justice something is given to
someone according to a kind of equality. In distributive justice this
equality regards personal dignity, which would seem to depend chiefly
on what a person has done for the good of the community; while in
commutative justice it regards the thing in which a person has
suffered loss. Now in respect of either equality there is retaliation
in respect of the deed committed. Therefore it would seem that the
just is absolutely the same as