Letters 124.12

And what is this Good? I shall tell you: it is a free mind, an upright mind, subjecting other things to itself and itself to nothing. So far is infancy from admitting this Good that boyhood has no hope of it, and even young manhood cherishes the hope without justification; even our old age is very fortunate if it has reached this Good after long and concentrated study. If this, then, is the Good, the good is a matter of the understanding.

Seneca, Letters to Lucilius 124.12, translated by Richard Mott Gummere