all future ages, we find the same three constituents of teaching as in Plato, and in the same order of importance: first, hearers selected for their natural aptitude, and then submitted to a moral discipline and a common life; secondly, the instruction of such hearers by word of mouth, question and answer, discussion and cross-examination; and lastly, the committing of doctrines to writing. With him too his written philosophical discourses were _reminders_ of his oral teaching, which they presupposed and required as a key to their full meaning, and especially for the comprehension of their harmony as a system. The order of teaching which I have thus sketched as being followed in practice by the two most eminent Greek philosophers belonged to them all. They had no other conception respecting the method of communicating a doctrine efficiently to men. None of them considered philosophy merely or chiefly as a literature: none of them attributed to a book the power of teaching it. Their conception was, a master and his scholars, and the living together, the moral subordination and discipline which this involved. This school of education or training in knowledge(399) was their primary thought: the committing of their doctrine to writing was both subsequent and secondary. Their writings were intended, as Plato says, to be recollections(400) of their teaching, and failed to convey the real knowledge to those who had not the stamp of this teaching impressed on their minds. As Plato made a local habitation for himself and his doctrine in the Academia, and Aristotle in the Lyceum, so Zeno, the founder of the third great philosophic school, took up his abode in the Portico at Athens, a court surrounded with pillars, and adorned with the paintings of Polygnotus. Here he began to teach about 308 B.C., and here he continued teaching as some say for fifty-eight years. It is said that the character of Socrates, as drawn by Xenophon and by Plato in his _Apology_, filled him with astonishment and admiration:(401) and the Stoics afterwards drew their doctrine of the wise man, which they endeavoured to image out and realise, from that living example of it,(402) an instance of the connection of doctrine with person which is full of interest and suggestion. Zeno was succeeded in his office of teaching by Cleanthes, and Cleanthes by Chrysippus and a long line of teachers, who for several hundred years continued, with variations, the same general doctrine of ethics.