
“There is only one good, knowledge, and one evil, ignorance.”
Socrates II: xxxi http://www.perseus.tufts.edu/hopper/text?doc=D.+L.+2.5.31&fromdoc=Perseus%3Atext%3A1999.01.0257#note-link14. Original Greek: ἓν μόνον ἀγαθὸν εἶναι, τὴν ἐπιστήμην, καὶ ἓν μόνον κακόν, τὴν ἀμαθίαν
Diogenes Laertius
Variant: The only good is knowledge and the only evil is ignorance.