This secondary education, beginning soon after fourteen, was only for the rich: the poor could not afford to keep their sons away from the farm or trade any longer. It might be scattered over the whole of the next six or seven years; but there was a serious interruption, which usually terminated it. At eighteen the young Athenian became in the eye of the law an ephebos and was called out to undergo two years of military training. During this period of conscription it was no doubt possible, especially in the laxer days of the fourth century, to do some intellectual work; but Plato is probably only accepting the usual custom when he frees the epheboi of his State from all mental studies and makes them give their whole energies to military and gymnastic training. And when the ephebos returned to civil life, he was a full citizen and was hardly likely to return to school; he might attend an occasional lecture or so, but that was all. Thus secondary education usually occupied the years between fourteen and eighteen, although the latter limit was in no way definitely fixed, and the same subjects might be studied at any age. In earlier days no doubt lads spent their time in continuing their musical studies: primary education could be conducted in a more leisurely fashion when there was still little to be learnt, and the lyre may have been deferred till this age, as Plato in similar circumstances defers it in the _Laws_. But in the days of Perikles knowledge began to increase and boys had more to learn. So the lyre was crowded into the first period of education, and a new series of secondary subjects arose. It was these years which were usually devoted to the four years’ course which was customary in the school of Isokrates. Before this date the time was, as a rule, spent in attending the lectures of the wandering Sophists or in picking up a smattering of philosophy. Among the subjects which thus formed a part of secondary education were mathematics of various kinds, more advanced literary criticism, a certain amount of natural history and science, a knowledge of the laws and constitution of Athens, a small quantity of philosophy, ethical, political, and metaphysical, and above all, rhetoric. Plato in his _Republic_, developing this Athenian system of secondary education, assigns to the years immediately preceding eighteen the theory of numbers, geometry, plane and solid, kinetics and harmonics, and expressly excludes dialectic as more suitable to a later age;[140] in the _Laws_, prescribing for the whole population, not for a few selected intellects, he orders practical arithmetic, geometry, and enough astronomy to make the calendar intelligible. The pseudo-Platonic _Axiochos_[141] ascribes to Prodikos the statement that “when a child grows older, he endures the tyranny of mathematicians, teachers of tactics, and ‘critics.’” These last are the professors of that curious criticism of poetry which is found, for