Q: Whether There Is a Different Matter for Both Kinds of Justice?

A: On the contrary,
It is stated in Ethic. v, 2 that "one kind of justice directs distributions, and another commutations."

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.