Objection 1. It would seem that justice is about the passions. For the Philosopher says (Ethic. ii, 3) that "moral virtue is about pleasure and pain." Now pleasure or delight, and pain are passions, as stated above [I-II, 23, 4; I-II, 31, 1; I-II, 35, 1] when we were treating of the passions. Therefore justice, being a moral virtue, is about the passions.
Objection 2. Further, justice is the means of rectifying a man's operations in relation to another man. Now such like operations cannot be rectified unless the passions be rectified, because it is owing to disorder of the passions that there is disorder in the aforesaid operations: thus sexual lust leads to adultery, and overmuch love of money leads to theft. Therefore justice must needs be about the passions.
Objection 3. Further, even as particular justice is towards another person so is legal justice. Now legal justice is about the passions, else it would not extend to all the virtues, some of which are evidently about the passions. Therefore justice is about the passions.
On the contrary, The Philosopher says (Ethic. v, 1) that justice is about operations.
I answer that, The true answer to this question may be gathered from a twofold source. First from the subject of justice, i.e. from the will, whose movements or acts are not passions, as stated above (I-II, 22, 3; I-II, 59, 4), for it is only the sensitive appetite whose movements are called passions. Hence justice is not about the passions, as are temperance and fortitude, which are in the irascible and concupiscible parts. Secondly, on he part of the matter, because justice is about man's relations with another, and we are not directed immediately to another by the internal passions. Therefore justice is not about the passions.
Reply to Objection 1. Not every moral virtue is about pleasure and pain as its proper matter, since fortitude is about fear and daring: but every moral virtue is directed to pleasure and pain, as to ends to be acquired, for, as the Philosopher says (Ethic. vii, 11), "pleasure and pain are the principal end in respect of which we say that this is an evil, and that a good": and in this way too they belong to justice, since "a man is not just unless he rejoice in just actions" (Ethic. i, 8).
Reply to Objection 2. External operations are as it were between external things, which are their matter, and internal passions, which are their origin. Now it happens sometimes that there is a defect in one of these, without there being a defect in the other. Thus a man may steal another's property, not through the desire to have the thing, but through the will to hurt the man; or vice versa, a man may covet another's property without wishing to steal it. Accordingly the directing of operations in so far as they tend towards external things, belongs to justice, but in so far as they arise from the passions, it belongs to the other moral virtues which are about the passions. Hence justice hinders theft of another's property, in so far as stealing is contrary to the, equality that should be maintained in external things, while liberality hinders it as resulting from an immoderate desire for wealth. Since, however, external operations take their species, not from the internal passions but from external things as being their objects, it follows that, external operations are essentially the matter of justice rather than of the other moral virtues.
Reply to Objection 3. The common good is the end of each individual member of a community, just as the good of the whole is the end of each part. On the other hand the good of one individual is not the end of another individual: wherefore legal justice which is directed to the common good, is more capable of extending to the internal passions whereby man is disposed in some way or other in himself, than particular justice which is directed to the good of another individual: although legal justice extends chiefly to other virtues in the point of their external operations, in so far, to wit, as "the law commands us to perform the actions of a courageous person... the actions of a temperate person... and the actions of a gentle person" (Ethic. v, 5).
Source: Summa Theologica (New Advent)