So Aristotle, Topica, III, 5 cf. Metaph. IX, vii, 7. St Thomas and Aristotle are fond of this illustration, that white is disgregativum visus, diakritikon opseôs and black congregativum, sugkritikon; but never explain it. It means that white, as representing light, is distinctive of vision, i.e., causes distinct vision; and black, as representing darkness, is confusive of vision. So, if all things were black -- the sun included, -- we should see nothing.

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