Isokrates is still more severe on various philosophical teachers; he cannot mean Plato alone, for he mentions their fees, and Plato made no charge. There must have been a large number of philosophical professors, of whom Plato was only the most brilliant. But in many points Isokrates no doubt meant his denunciations to apply to Plato also. The summary of his attack is as follows:――“They make impossible offers, promising to impart to their pupils an exact science of conduct, by means of which they will always know what to do. Yet for this science they charge only 3 or 4 μναῖ [mnai] (£12 or £16), a ridiculously small sum. They try to attract pupils by the specious titles of the subjects which they claim to teach, such as Justice and Prudence. But the Justice and the Prudence which they teach are of a very peculiar sort, and they give a meaning to the words quite different from that which ordinary people give; in fact, they cannot be sure about the meaning themselves, but can only dispute about it. Although they profess to teach Justice, they refuse to trust their pupils, but make them deposit the fees with a third party before the course begins.”[533] Here we have a picture of a distinct group of ethical teachers all trying to work at that Socratic paradox that virtue is knowledge, and imparting their results to pupils for low fees. All these Professors of Ethics seem to have made Mathematics and Astronomy a part of their course, just as Plato did. “To the old Athenian education, of Letters and Music and Gymnastics, they have added a more advanced course, consisting of Geometry and Astronomy and such subjects, together with eristic dialogues,” that is, Dialectic.[534] This course seems to have been much criticised as being a mere waste of time, since it was of no practical use and the knowledge so obtained was soon forgotten in after life. But Isokrates, although these subjects played no part in his own school, was sufficiently good an educationalist to see their merits: the study of subtle and difficult matters like Astronomy and Geometry “trains a boy to keep his attention closely fixed upon the point at issue and not to allow his mind to wander; so, being practised in this way and having his wits sharpened, he will be made capable of learning more important matters with greater ease and speed.”[535] But all these unpractical, if improving, studies should be abandoned before the nineteenth year: for they dry up the human nature and make men unbusinesslike. “Some of those who have become so adept in these subjects that they teach them to others, show themselves in the practical conduct of life less wise than their pupils, not to say than their servants.”[536] Consequently, those who care to study mathematics and eristic should confine them to the years between fourteen and eighteen: and then pass on to learn rhetoric with Isokrates; the rest can come to his school as lads, as many did.