Philosophers may be divided into dogmatists and sceptics: all those who make assertions about things assuming that they can be known are dogmatists; while all who suspend their judgement on the ground that things are unknowable are sceptics. Again, some philosophers left writings behind them, while others wrote nothing at all, as was the case according to some authorities with Socrates, Stilpo, Philippus, Menedemus, Pyrrho, Theodorus, Carneades, Bryson; some add Pythagoras and Aristo of Chios, except that they wrote a few letters. Others wrote no more than one treatise each, as Melissus, Parmenides, Anaxagoras. Many works were written by Zeno, more by Xenophanes, more by Democritus, more by Aristotle, more by Epicurus, and still more by Chrysippus.

Some schools took their name from cities, as the Elians and the Megarians, the Eretrians and the Cyrenaics; others from localities, as the Academics and the Stoics; others from incidental circumstances, as the Peripatetics; others again from derisive nicknames, as the Cynics; others from their temperaments, as the Eudaemonists or Happiness School; others from a conceit they entertained, as Truthlovers, Refutationists, and Reasoners from Analogy; others again from their teachers, as Socratics, Epicureans, and the like; some take the name of Physicists from their investigation of nature, others that of Moralists because they discuss morals; while those who are occupied with verbal jugglery are styled Dialecticians.

Philosophy has three parts, physics, ethics, and dialectic or logic. Physics is the part concerned with the universe and all that it contains; ethics that concerned with life and all that has to do with us; while the processes of reasoning employed by both form the province of dialectic. Physics flourished down to the time of Archelaus; ethics, as we have said, started with Socrates; while dialectic goes as far back as Zeno of Elea. In ethics there have been ten schools: the Academic, the Cyrenaic, the Elian, the Megarian, the Cynic, the Eretrian, the Dialectic, the Peripatetic, the Stoic, and the Epicurean.

The founders of these schools were: of the Old Academy, Plato; of the Middle Academy, Arcesilaus; of the New Academy, Lacydes; of the Cyrenaic, Aristippus of Cyrene; of the Elian, Phaedo of Elis; of the Megarian, Euclides of Megara; of the Cynic, Antisthenes of Athens; of the Eretrian, Menedemus of Eretria; of the Dialectical school, Clitomachus of Carthage; of the Peripatetic, Aristotle of Stagira; of the Stoic, Zeno of Citium; while the Epicurean school took its name from Epicurus himself.

Hippobotus in his work On Philosophical Sects declares that there are nine sects or schools, and gives them in this order: (1) Megarian, (2) Eretrian, (3) Cyrenaic, (4) Epicurean, (5) Annicerean,The separation of the followers of Anniceris from the Cyrenaic school was made by the author whom Clement of Alexandria followed in ii. 130. This author may have been Antiochus of Ascalon. Strabo x. 837 s.f. supports the same view: Ἀννίκερις ὁ δοκῶν ἐπανορθῶσαι τὴν Κυρηναϊκὴν αἵρεσιν, καὶ παραγαγεῖν ἀντ’ αὐτῆς τὴν Ἀννικερείαν., (6) Theodorean, (7) Zenonian or Stoic, (8) Old Academic, (9) Peripatetic.

He passes over the Cynic, Elian, and Dialectical schools; for as to the Pyrrhonians, so indefinite are their conclusions that hardly any authorities allow them to be a sect; some allow their claim in certain respects, but not in others. It would seem, however, that they are a sect, for we use the term of those who in their attitude to appearance follow or seem to follow some principle; and on this ground we should be justified in calling the Sceptics a sect. But if we are to understand by sect a bias in favour of coherent positive doctrines, they could no longer be called a sect,Cf. the distinction drawn by Sextus Empiricus in Pyrrh. Hyp. i. 16, 17. If by rules for conduct dogmas are implied, then the Pyrrhonians are not a sect, i.e. a dogmatic school., for they have no positive doctrines. So much for the beginnings of philosophy, its subsequent developments, its various parts, and the number of the philosophic sects.