Proclus, The philosophical and mathematical commentaries of Proclus on the first book of Euclid's elements… (1791)
“ Lastly, sagacity is an acute and sudden apprehension of the medium, or proper cause of a certain effect: as if any one, beholding the moon, should in a moment conjecture the cause of the part opposite to the sun being lucid, and the other parts obscure, because she derives her splendor from the sun. ”
