What I mean, for example, is this; the same sense no doubt discerns white and black, though they are specifically different from one another, and so, too, a faculty of sense self identical, but different from the former, discerns sweet and bitter; but while both these faculties differ from one another in their modes of discerning either of their respective contraries, yet in perceiving the co ordinates in each province they proceed in manners analogous to one another; for instance, as taste perceives sweet, so sight perceives white; and as the latter perceives black, so the former perceives bitter.