There Is Only One Good Knowledge

Diogenes Laertius records this saying in Lives of the Eminent Philosophers (3rd century AD), one of the most important biographical sources for ancient Greek thinkers. It captures a core Socratic conviction — shared across Plato's and Xenophon's accounts — that all wrongdoing stems from ignorance. If a person truly knows what is good, Socrates argued, they will necessarily act rightly, a position known as Socratic intellectualism.