retaliation.

Obj. 3: Further, the chief argument against retaliation is based on
the difference between the voluntary and the involuntary; for he who
does an injury involuntarily is less severely punished. Now voluntary
and involuntary taken in relation to ourselves, do not diversify the
mean of justice since this is the real mean and does not depend on
us. Therefore it would seem that the just is absolutely the same as
retaliation.

_On the contrary,_ The Philosopher proves (Ethic. v, 5) that the just
is not always the same as retaliation.

_I answer that,_ Retaliation (_contrapassum_) denotes equal passion
repaid for previous action; and the expression applies most properly
to injurious passions and actions, whereby a man harms the person of
his neighbor; for instance if a man strike, that he be struck back.
This kind of just is laid down in the Law (Ex. 21:23, 24): "He shall
render life for life, eye for eye," etc. And since also to take away
what belongs to another is to do an unjust thing, it follows that
secondly retaliation consists in this also, that whosoever causes
loss to another, should suffer loss in his belongings. This just loss
is also found in the Law (Ex. 22:1): "If any man steal an ox or a
sheep, and kill or sell it, he shall restore five oxen for one ox and
four sheep for one sheep." Thirdly retaliation is transferred to
voluntary commutations, where action and passion are on both sides,
although voluntariness detracts from the nature of passion, as stated
above (Q. 59, A. 3).

In all these cases, however, repayment must be made on a basis of
equality according to the requirements of commutative justice, namely
that the meed of passion be equal to the action. Now there would not
always be equality if passion were in the same species as the action.
Because, in the first place, when a person injures the person of one
who is greater, the action surpasses any passion of the same species
that he might undergo, wherefore he that strikes a prince, is not
only struck back, but is much more severely punished. In like manner
when a man despoils another of his property against the latter's
will, the action surpasses the passion if he be merely deprived of
that thing, because the man who caused another's loss, himself would
lose nothing, and so he is punished by making restitution several
times over, because not only did he injure a private individual, but
also the common weal, the security of whose prote