indignatio

Indignatio in Latin means anger at something unworthy or unjust, from indignus (unworthy, undeserved), from in- (not) + dignus (worthy). The word specifies its own cause: indignation is anger at unworthiness — at treatment that the recipient does not deserve, at behavior that violates what is right. Juvenal, the Roman satirist, wrote in the early second century CE: 'si natura negat, facit indignatio versum' — if nature denies the talent, indignation will write the verse.

Aristotle had analyzed the emotion in the Rhetoric (~350 BCE) as nemesis — righteous anger at undeserved fortune, whether good or bad. Someone unworthy getting rewarded produces indignation. Someone worthy getting punished produces indignation. The emotion is structurally moral: it requires a judgment about what someone deserves. This distinguishes it from anger (which can be irrational) and resentment (which can be petty).

The eighteenth century made indignation a political virtue. The indignation of the people against tyranny was a cornerstone of revolutionary rhetoric. Thomas Paine's Common Sense (1776) runs on indignation. So does Frederick Douglass's 'What to the Slave Is the Fourth of July?' (1852). Indignation is the emotion that says: this is wrong, and I will not be silent about it.

Modern usage has slightly weakened the word. 'Indignant' can now describe someone who is offended on their own behalf, not necessarily on behalf of justice. 'She was indignant that her parking spot was taken' stretches the word beyond its original meaning. But the core sense persists: indignation is anger that believes itself justified. Whether it is justified is a separate question.