ARCADIUS

arcadius, of antioch, greek grammarian, flourished in the 2nd century a.d. according to suidas, he wrote treatises on orthography and syntax, and an onomaticon (vocabulary), described as a wonderful production. an epitome of the great work of herodian on general prosody in twenty books, wrongly attributed to arcadius, is probably the work of theodosius of alexandria or a grammarian named aristodemus. this epitome ([greek: peri tonon]) only includes nineteen books of the original work; the twentieth is the work of a forger of the 16th century. although meagre and carelessly put together, it is valuable, since it preserves the order of the original and thus affords a trustworthy foundation for its reconstruction. text by barker, 1823; schmidt, 1860; see also galland, _de arcadii qui fertur libra de accentibus_ (1882). arcella (c.g. ehrenberg), a genus of lobose rhizopoda, characterized by a chitinous plano-convex shell, the circular aperture central on the flat ventral face, and more than one nucleus and contractile vacuole. it can develop vacuoles, or rather fine bubbles of carbonic acid gas in its cytoplasm, to float up to the surface of the water. arcesilaus (316-241 b.c.), a greek philosopher and founder of the new, or middle, academy (see academy, greek). born at pitane in aeolis, he was trained by autolycus, the mathematician, and later at athens by theophrastus and crantor, by whom he was led to join the academy. he subsequently became intimate with polemon and crates, whom he succeeded as head of the school. diogenes laertius says that he died of excessive drinking, but the testimony of others (e.g. cleanthes) and his own precepts discredit the story, and he is known to have been much respected by the athenians. his doctrines, which must be gathered from the writings of others (cicero, _acad._ i. 12, iv. 24; _de orat._ iii. 18; diogenes laertius iv. 28; sextus empiricus, _adv. math._ vii. 150, _pyrrh. hyp._ i. 233), represent an attack on the stoic [greek: phantasia katalaeptikae] (_criterion_) and are based on the sceptical element (see scepticism) which was latent in the later writings of plato. he held that strength of intellectual conviction cannot be regarded as valid, inasmuch as it is characteristic equally of contradictory convictions. the uncertainty of sensible _data_ applies equally to the conclusions of reason, and therefore man must be content with _probability_ which is sufficient as a practical guide. "we know nothing, not even our ignorance"; therefore the wise man will be content with an agnostic attitude. he made use of the socratic method of instruction and left no writings. his arguments were marked by incisive humour and fertility of ideas. see r. brodeisen, _de arcesila philosopho_ (1821); aug. geffers, _de arcesila_ (1842); ritter and preller, _hist, philos. graec._ (1898); ed. zeller, _phil. d. griech._ (iii. 1448); and general works under scepticism.