Aristotle's lectures to his disciples were of two kinds, exoteric and acromatic. The acromatic were those, to which only his own disciples and intimate friends were admitted; whereas the exoteric were public and open to all. But there are other differences. The acromatic were set apart for the higher and more abstruse subjects; the exoteric were employed in rhetorical and civil speculations. Again, the acromatic were more subtile and exact, evidence and demonstration being here aimed at; the exoterics chiefly aimed at the probable and plausible. The former were the subject of the mornings exercises in the Lyceum, the latter of the evenings. Add, that the exoterics were published; whereas the acromatic were kept secret; being either entirely concealed; or if they were published, it was in such obscure terms, that few but his own disciples would be the wiser for them. Hence, when Alexander complained of his preceptor for publishing his acromatic, and thus revealing what should have been referred to his disciples, Aristotle answered, that they were made public and not public; for that none who had not heard them explained by the author vivæ voce, would understand them.

ACROTHOUM, or Acrothoum, (anc. geogr.) a town situated on the top of mount Athos, where the inhabitants, according to Mela, were longer lived by half than in any other country: called by the modern Greeks, Ἀγροτός; by the Italians, La Cima di Monte Santo.