I answer that, As stated above (Q. 51, AA. 8, 10), justice is about certain external operations, namely distribution and commutation. These consist in the use of certain externals, whether things, persons or even works: of things, as when one man takes from or restores to another that which is his; of persons, as when a man does an injury to the very person of another, for instance by striking or insulting him, or even by showing respect for him; and of works, as when a man justly exacts a work of another, or does a work for him. Accordingly, if we take for the matter of each kind of justice the things themselves of which the operations are the use, the matter of distributive and commutative justice is the same, since things can be distributed out of the common property to individuals, and be the subject of commutation between one person and another; and again there is a certain distribution and payment of laborious works.
If, however, we take for the matter of both kinds of justice the principal actions themselves, whereby we make use of persons, things, and works, there is then a difference of matter between them. For distributive justice directs distributions, while commutative justice directs commutations that can take place between two persons. Of these some are involuntary, some voluntary. They are involuntary when anyone uses another man's chattel, person, or work against his will, and this may be done secretly by fraud, or openly by violence. In either case the offence may be committed against the other man's chattel or person, or against a person connected with him. If the offence is against his chattel and this be taken secretly, it is called "theft," if openly, it is called "robbery." If it be against another man's person, it may affect either the very substance of his person, or his dignity. If it be against the substance of his person, a man is injured secretly if he is treacherously slain, struck or poisoned, and openly, if he is publicly slain, imprisoned, struck or maimed. If it be against his personal dignity, a man is injured secretly by false witness, detractions and so forth, whereby he is deprived of his good name, and openly, by being accused in a court of law, or by public insult. If it be against a personal connection, a man is injured in the person of his wife, secretly (for the most part) by adultery, in the person of his slave, if the latter be induced to leave his master: which things can also be done openly. The same applies to other personal connections, and whatever injury may be committed against the principal, may be committed against them also. Adultery, however, and inducing a slave to leave his master are properly injuries against the person; yet the latter, since a slave is his master's chattel, is referred to theft. 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 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 protection he has infringed. Nor again would there be equality of passion in voluntary commutations, were one always to exchange one's chattel for another man's, because it might happen that the other man's chattel is much greater than our own: so that it becomes necessary to equalize passion and action in commutations according to a certain proportionate commensuration, for which purpose money was invented. Hence retaliation is in accordance with commutative justice: but there is no place for it in distributive justice, because in distributive justice we do not consider the equality between thing and thing or between passion and action (whence the expression contrapassum), but according to proportion between things and persons, as stated above (A. 2).