Wer nicht um der Philosophie willen philosophiert, sondern die Philosophie als Mittel braucht, ist ein Sophist. - sophist

To offer one’s beauty for money to all comers is called prostitution; but we think it virtuous to become friendly with a lover who is known to be a man of honour. So is it with wisdom. Those who offer it to all comers for money are known as sophists, prostitutors of wisdom.

It is what a man has thought out directly for himself that alone has true value. Thinkers may be classed as follows: those who, in the first place, think for themselves, and those who think directly for others. The former thinkers are the genuine, they think for themselves in both senses of the word; they are the true philosophers; they alone are in earnest. Moreover, the enjoyment and happiness of their existence consist in thinking. The others are the sophists; they wish to seem, and seek their happiness in what they hope to get from other people; their earnestness consists in this.

Is not a Sophist, Hippocrates, one who deals wholesale or retail in the food of the soul? To me that appears to be his nature. … Knowledge is the food of the soul; and we must take care, my friend, that the Sophist does not deceive us when he praises what he sells, like the dealers wholesale or retail who sell the food of the body; for they praise indiscriminately all their goods, without knowing what are really beneficial or hurtful. Neither do their customers know … unless he who buys of them happens to be a physician of the soul.