ACATALESSIA. — From Greek ἀκαταληψία (a privative prefix and καταλαμβάνω, *percipio*, *comprehend*), it is the impossibility of apprehending the truth. The noun form first appears in the vocabulary in Cicero (Att. 13, 19, 3), then in Sextus Empiricus and Diogenes Laertius (cf. prooem. 16), but the corresponding adjective ἀκατάληψιος is older and dates back to the Stoics, who used it in conjunction with φαντασία (*representation*) to distinguish that which does not correspond to reality or pertains to a non-existent object from that which arises from a real object and corresponds to it, the latter being called καταληπτική or καταληψία (Cic., Acad., II, 145: “Zeno... imposed a name... which had not existed before”).
Outside of this technical usage, ἀκατάληψιος meant “not knowable in its reality.” That all things were of this nature was taught simultaneously by Pyrrho of Elis (early 3rd century B.C.), founder of the Skeptical School, and Arcesilaus (315–241), who gave the Middle Academy its skeptical direction, which it maintained until Philo of Larissa, Cicero’s teacher. A direct consequence of acatalepsia was the suspension of judgment (ἐποχή), and in the practical sphere, the pursuit of ataraxia or freedom from disturbance, also called apathy. The term was taken up by Bacon in the sense of skeptical doubt, which he opposed to methodological doubt: cf. Nov. Org., I, 126: “nos vero non acatalepsiam sed cucatalepsiam meditamur.”