/summa/SS/SSII/SS_Q79:
We must now consider the quasi-integral parts of justice, which are "to do good," and "to decline from evil," and the opposite vices. Under this head there are four points of inquiry:
(1) Whether these two are parts of justice?
(2) Whether transgression is a special sin?
(3) Whether omission is a special sin?
(4) Of the comparison between omission and transgression.