HKB
anger, when, to wit, one is angry, more or less than right reason demands. But if one is angry in accordance with right reason, one's anger is deserving of praise.
Reply Obj. 1: The Stoics designated anger and all the other passions as emotions opposed to the order of reason; and accordingly they deemed anger and all other passions to be evil, as stated above (I-II, Q. 24, A. 2) when we were treating of the passions. It is in this sense that Jerome considers anger; for he speaks of the anger whereby one is angry with one's neighbor, with the intent of doing him a wrong.--But, according to the Peripatetics, to whose opinion Augustine inclines (De Civ. Dei ix, 4), anger and the other passions of the soul are movements of the sensitive appetite, whether they be moderated or not, according to reason: and in this sense anger is not always evil.
Reply Obj. 2: Anger may stand in a twofold relation to reason. First, antecedently; in this way it withdraws reason from its rectitude, and has therefore the character of evil. Secondly, consequently, inasmuch as the movement of the sensitive appetite is directed against vice and in accordance with reason, this anger is good, and is called "zealous anger." Wherefore Gregory says (Moral. v, 45): "We must beware lest, when we use anger as an instrument of virtue, it overrule the mind, and go before it as its mistress, instead of following in reason's train, ever ready, as its handmaid, to obey." This latter anger, although it hinder somewhat the judgment of reason in the execution of the act, does not destroy the rectitude of reason. Hence Gregory says (Moral. v, 45) that "zealous anger troubles the eye of reason, whereas sinful anger blinds it." Nor is it incompatible with virtue that the deliberation of reason be interrupted in the execution of what reason has deliberated: since art also would be hindered in its act, if it were to deliberate about what has to be done, while having to act.
Reply Obj. 3: It is unlawful to desire vengeance considered as evil to the man who is to be punished, but it is praiseworthy to desire vengeance as a corrective of vice and for the good of justice; and to this the sensitive appetite can tend, in so far as it is moved thereto by the reason: and when revenge is taken in accordance with the order of judgment, it is God's work, since he who has power to punish "is God's minister," as stated in Rom. 13:4.
Reply Obj. 4: We can and ought to be like to God in the desire for good; but we cannot be altogether likened to Him in the mode of our desire, since in God there is no sensitive appetite, as in us, the movement of which has to obey reason. Wherefore Gregory says (Moral. v, 45) that "anger is more firmly erect in withstanding vice, when it bows to the command of reason."
SECOND ARTICLE [II-II, Q. 158, Art. 2]
Whether Anger Is a Sin?
Objection 1: It would seem that anger is not a sin. For we demerit by sinning. But "we do not demerit by the passions, even as neither do we incur blame thereby," as stated in Ethic. ii, 5. Consequently no passion is a sin. Now anger is a passion as stated above (I-II, Q. 46, A. 1) in the treatise on the passions. Therefore anger is not a sin.
Obj. 2: Further, in every sin there is conversion to some mutable good. But in anger there is conversion not to a mutable good, but to a person's evil. Therefore anger is not a sin.