Hence he had been well trained even before he left his native place. And thus it came about that on his arrival at Athens he attached himself to Crates. And it seems, he adds, that, when the rest were at a loss how to express their views, Zeno framed a definition of the end. They say that he was in the habit of swearing by “capers” just as Socrates used to swear by “the dog.” Some there are, and among them Cassius the Sceptic and his disciples, who accuse Zeno at length. Their first count is that in the beginning of his Republic he pronounced the ordinary education useless: the next is that he applies to all men who are not virtuous the opprobrious epithets of foemen, cnemies, slaves, and aliens to one another, parents to children, brothers to brothers, friends to friends.
Lives of the Eminent Philosophers (1925) by Diogenes Laërtius, translated by Robert Drew Hicks