Aristotle's Ethics by Aristotle

Gentleness or good temper is the mean in feelings of anger. Short temper or irascibility is the excess, the deficiency has no name but may be called insufficient anger or apathy. The emotion of anger can be caused by many different factors, but the good-tempered man is always angry under the right circumstances, with the right people, in the right manner and degree, at the right time, and for the right length of time. Excess can be shown in too much anger, or unjustified anger, or too lengthy anger, etc. Apathy is the vice of those who do not get angry when anger is justified and who are not affected by things that should arouse anger; apathetic people often seem to have no feelings and to be unable to suffer pain for any reason.