ARCESILAUS (316-241 B.c.), Athenian philosopher and founder of the New, or Middle, Academy (see ACADEMY, GREEK). His doctrines, which must be gathered from the writings of others (Cicero, Acad., i. 12,1V. 24; De Orat., III. 18; Diogenes Laertius iv. 28; Sextus Empiricus, Adv. Math., vii. 15o, Pyrrh. Hyp. i. 233), represent an attack on the Stoic 4avracria KaraX7)7rTCa? (Criterion). He held that strength of intellectual conviction can not be regarded as valid. 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.