This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Of all the passions Stoic writers catalogued, Seneca treated anger as the one that most urgently demanded its own book-length treatment, and his De Ira is his fullest study of a single emotion. His starting definition is precise, anger is a species of desire, specifically the desire for revenge against someone believed to have done a wrong. Built into that definition is a judgment, and this is the detail that gives the whole treatise its argumentative force. Anger does not simply happen to a person the way a chill or a flush happens to the body. It requires the mind to have first judged that a wrong occurred and that revenge is the fitting response, and Seneca's entire strategy for handling anger depends on exposing and examining that judgment rather than trying to suppress the feeling that follows from it.
This leads Seneca to the position that made his treatise distinctive among ancient discussions of emotion, that anger cannot be moderated, only eliminated. Other schools, and even some Stoic predecessors on other passions, had proposed trimming excessive emotion down to a reasonable amount, keeping a little anger on hand as a spur to right action. Seneca will not accept the compromise. He compares the notion of moderate anger to the notion of moderate insanity, an idea that dissolves once stated plainly, since insanity is by definition the loss of the very faculty that would let a person moderate anything. Anger, once it has seized the reasoning mind, is not a controlled tool that reason can dial up or down, it is reason's temporary abdication, and a little abdication is still an abdication. The remedy therefore cannot be a smaller dose of the same disease. It has to be the substitution of a different motive altogether, so that the wise person who corrects a wrongdoer does so calmly, because correction is fitting and useful, and not because any flare of resentment demanded an outlet.
Seneca is careful, in ways later readers have found psychologically astute, to distinguish the involuntary jolt that follows a sudden shock or insult from anger proper. A flinch, a reddening face, a racing pulse at an unexpected blow are automatic bodily reactions that even the sage cannot fully prevent, since they occur before any judgment has had time to form. Anger in the full sense begins only when the mind endorses that first jolt, assents to the story that a wrong has been done and revenge is owed, and commits itself to acting on that assent. This distinction let Seneca hold two things at once that might otherwise seem contradictory, that the wise person remains recognizably human, subject to being startled or stung in the moment, while still being genuinely free of anger as a settled state, because freedom from anger was never a matter of feeling nothing but of refusing the further step of endorsement. The practical portions of the treatise, which catalogue methods for preventing anger's onset, for delaying any response until the initial impression cools, and for training children and rulers alike out of vengeful habits, all follow from this diagnosis. If anger is a judgment that the mind actively makes rather than a weather system that passes through it, then the mind can also be trained not to make that judgment, and that training, not restraint of an already kindled fire, is where Seneca places the entire cure.