MARCUS AURELIUS. MEDITATIONS. Book viii. 41.WHEN one consulted him, how he might persuade his brother to forbear treating him ill: Philosophy, answered Epictetus, doth not promise to procure anything external to man, otherwise it would admit something beyond its proper subject-matter. For the subject-matter of a carpenter is wood; of a statuary, brass: and so of the art of living, the subject-matter is each person's own life.
EPICTETUS. DISCOURSES. Book i. §15. ¶1.