The two important documents for the ‘philosophy’ of Isokrates are the discourse Against the Sophists (Or. XIII. 391 B. C.), and the speech On the Antidosis (Or. XV. 353 B.C.), the alpha and the omega of his professional life. In the first of these he declares what his ‘philosophy’ is not; in the second he explains what it is.

It is distinguished, then,—first, from all theoretic ¹ inquiries, as from those of the Ionic physicists, and from the ethical and political speculations of the Sokratic schools. Secondly, from Eristic, or the art of disputing for disputation's sake. Thirdly, from mathematical science. Fourthly, from all literary activity which has no direct bearing on the higher political life: as (i) mythological research, ‘genealogies of the heroes,’ and the like; (ii) history, considered as the compiling of annals, apart from political essay-writing; (iii) philology and criticism of the poets; (iv) rhetoric applied to low or trivial subjects, whether forensic, or of the sportive epideiktic kind ² .

It forms the last and highest department of the ³ citizen's education. Boys at school learn grammar and read the poets. Older youths may profitably study astronomy or geometry up to a certain point, for the purpose of sharpening their faculties; a profound study of these subjects is useful only for professional specialists ⁴ . Eristic may be used for practice in the same way; but the student must take care that his nature is not ‘dried up by it,’ and that he is not ‘stranded’ in such barren subtleties as (for instance) those of Empedokles and Parmenides ⁵ . Then, when the faculties have been thus prepared and trained, ‘philosophy’ comes in. What Gymnastic is for the body, Philosophy is for the mind. The teacher of Gymnastic practises his pupils in all the artificial exercises ( σχήματα) which have been devised as preparatives for real contests. The teacher of Philosophy trains his pupils in all the artificial resources ⁶ which prose-composition can employ. Then he tries them in real work, in putting together ( συνείρειν) the particular things which they have learned, so that they may grasp them more firmly, and may be able to use them readily in any combination which any given occasion may require. It is impossible to foresee exactly all these occasions; there can be no science of them. There can only be opinion, conjecture about them; and he is the wisest man who—exact foresight being out of the question —can best conjecture what any given crisis will demand of him ⁷ . ‘Philosophy’ cannot of itself engage to produce a man able to speak and to act. Three things go to make such a man—natural capacity, training, and practical experience. The second has no power comparable to that of the first and third. All that training can infallibly do is to make the man better ⁸ . And what is of supreme importance is the class of subjects to which the oratorical and literary faculty, as it grows, is turned. These must be (1) practical; (2) concerned with the largest public interests;—not with such private interests as employ forensic rhetoric, nor even with the exclusive interests of a single city ⁹ . Isokrates cites from his own works two examples of such ‘nationally political,’ Hellenic subjects: one is the thesis—‘Athens has a better right than Lacedaemon to the hegemony ¹⁰ ’; another is—‘What measures are needed to reform the foreign and home policy of Athens ¹¹ ?’