Heraclitus

(c. 540 BC - c. 480 BC)

All of the philosopher Heraclitus’ extant thoughts, believed to have been contained originally in one book, exist as fragments quoted in the works of later writers, among them Aristotle, Marcus Aurelius, Sextus Empiricus, and Diogenes Laërtius. Among the defining characteristics of Heraclitus’ conception of the world are the “logos”—a reason and order that the harmonious yet fluctuating universe can convey to the wise man—and elemental fire, which constitutes the soul of man.