“And,” said I, “will we not say, Adeimantus, that the same applies to souls? Those with the best natural endowments will become especially bad on encountering bad instruction. Or do you think that enormous injustices and unadulterated baseness originate in an ordinary nature, rather than in a high-spirited nature corrupted by its nurture? Will a weak nature ever be responsible for any great good or any great evil?”
“No,” he said, “the situation is as you describe it.”
“Then, I presume, the nature we designated as philosophic must develop and attain complete excellence if it obtains the proper instruction. However, if it is not sown, planted and nurtured in the proper manner, it attains the very opposite instead, unless one of the gods happens to come to its aid.
“Or do you also believe, as many do, that some young people are corrupted by sophists, and that certain sophists, operating in private, are a corrupting influence of any significance? Rather, is it not the very people who make these statements who are the greatest sophists, who educate young and old, men and women, to the utmost, and fashion them according to their will?”
Plato, Republic VI, 491e-492b