I will also set down his and any other utterance of his that seems worth citing, that you may be in a position to study the philosopher on all sides and know how to judge him.

The first epistle is addressed to Herodotus and deals with physics; the second to Pythocles and deals with astronomy or meteorology; the third is addressed to Menoeceus and its subject is human life. We must begin with the first after some few preliminary remarksi.e.§§ 29-34, the first of those summaries of doctrine which take up so much of Book X. upon his division of philosophy.

It is divided into three parts—Canonic, Physics, Ethics.