[139] And the whole company of students of philosophy may argue with them on their line of conduct, each going through the studies to which he is accustomed; because, of all existing things some are corporeal, and some incorporeal; some again are inanimate, and some have vitality; some are endowed with, others destitute of reason; some are mortal, others divine; and of mortals some are male, and some female, these being the two divisions of the human race.