1265–1273 · Thomas Aquinas, Summa Theologica II-II, q. 158, a. 2, co.
A passion of the sensitive appetite is good in so far as it is regulated by reason, whereas it is evil if it set the order of reason aside. Now the order of reason, in regard to anger, may be considered in relation to two things. First, in relation to the appetible object to which anger tends, and that is revenge. Wherefore if one desire revenge to be taken in accordance with the order of reason, the desire of anger is praiseworthy, and is called "zealous anger" [*Cf. Greg., Moral. v, 45]. On the other hand, if one desire the taking of vengeance in any way whatever contrary to the order of reason, for instance if he desire the punishment of one who has not deserved it, or beyond his deserts, or again contrary to the order prescribed by law, or not for the due end, namely the maintaining of justice and the correction of defaults, then the desire of anger will be sinful, and this is called sinful anger. Secondly, the order of reason in regard to anger may be considered in relation to the mode of being angry, namely that the movement of anger should not be immoderately fierce, neither internally nor externally; and if this condition be disregarded, anger will not lack sin, even though just vengeance be desired.