Summa Theologica, Part I-II (Pars Prima Secundae)
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Those moral virtues, however, which are not about the passions, but about operations, can be without passions. Such a virtue is justice: because it applies the will to its proper act, which is not a passion. Nevertheless, joy results from the act of justice; at least in the will, in which case it is not a passion. And if this joy be increased through the perfection of justice, it will overflow into the sensitive appetite; in so far as the lower powers follow the movement of the higher. Wherefore by reason of this kind of overflow, the more perfect a virtue is, the more does it cause passion.