The tremendous influence Stoicism has exerted on ethical thought from early Christianity through Immanuel Kant and into the twentieth century is rarely understood and even more rarely appreciated. Throughout history, Stoic ethical doctrines have both provoked harsh criticisms and inspired enthusiastic defenders. The Stoics defined the goal in life as living in agreement with nature. Humans, unlike all other animals, are constituted by nature to develop reason as adults, which transforms their understanding of themselves and their own true good. The Stoics held that virtue is the only real good and so is both necessary and, contrary to Aristotle, sufficient for happiness; it in no way depends on luck. The virtuous life is free of all passions, which are intrinsically disturbing and harmful to the soul, but includes appropriate emotive responses conditioned by rational understanding and the fulfillment of all one's personal, social, professional, and civic responsibilities. The Stoics believed that the person who has achieved perfect consistency in the operation of his rational faculties, the "wise man," is extremely rare, yet serves as a prescriptive ideal for all. The Stoics believed that progress toward this noble goal is both possible and vitally urgent.
The soul of the virtuous person, in contrast, is possessed of three good states or affective responses (eupatheiai). The three