I answer that, A human virtue is one "which renders a human act and man himself good" [*Ethic. ii, 6], and this can be applied to justice. For a man's act is made good through attaining the rule of reason, which is the rule whereby human acts are regulated. Hence, since justice regulates human operations, it is evident that it renders man's operations good, and, as Tully declares (De Officiis i, 7), good men are so called chiefly from their justice, wherefore, as he says again (De Officiis i, 7) "the luster of virtue appears above all in justice."
Reply Obj. 1: When a man does what he ought, he brings no gain to the person to whom he does what he ought, but only abstains from doing him a harm. He does however profit himself, in so far as he does what he ought, spontaneously and readily, and this is to act virtuously. Hence it is written (Wis. 8:7) that Divine wisdom "teacheth temperance, and prudence, and justice, and fortitude, which are such things as men (i.e. virtuous men) can have nothing more profitable in life."
Reply Obj. 2: Necessity is twofold. One arises from constraint, and this removes merit, since it runs counter to the will. The other arises from the obligation of a command, or from the necessity of obtaining an end, when, to wit, a man is unable to achieve the end of virtue without doing some particular thing. The latter necessity does not remove merit, when a man does voluntarily that which is necessary in this way. It does however exclude the credit of supererogation, according to 1 Cor. 9:16, "If I preach the Gospel, it is no glory to me, for a necessity lieth upon me."
Reply Obj. 3: Justice is concerned about external things, not by making them, which pertains to art, but by using them in our dealings with other men. _______________________
FOURTH ARTICLE [II-II, Q. 58, Art. 4]
Whether Justice Is in the Will As Its Subject?
Objection 1: It would seem that justice is not in the will as its subject. For justice is sometimes called truth. But truth is not in the will, but in the intellect. Therefore justice is not in the will as its subject.
Obj. 2: Further, justice is about our dealings with others. Now it belongs to the reason to direct one thing in relation to another. Therefore justice is not in the will as its subject but in the reason.
Obj. 3: Further, justice is not an intellectual virtue, since it is not directed to knowledge; wherefore it follows that it is a moral virtue. Now the subject of moral virtue is the faculty which is "rational by participation," viz. the irascible and the concupiscible, as the Philosopher declares (Ethic. i, 13). Therefore justice is not in the will as its subject, but in the irascible and concupiscible.
On the contrary, Anselm says (De Verit. xii) that "justice is rectitude of the will observed for its own sake."