Date: 380-360 B.C.

"'All of you in the city are certainly brothers,' we shall say to them in telling the tale, 'but god, in fashioning those of you who are competent to rule, mixed gold in at their birth; this is why they are most honored; in auxiliaries, silver, and iron and bronze in the farmers and other craftsm...

— Plato (427 BC - 347 BC)

Date: 380-360 B.C.

"Hence the god commands the rulers first and foremost to be of nothing such good guardians and to keep over nothing so careful a watch as the children, seeing which of these metals is mixed in their souls."

— Plato (427 BC - 347 BC)

Date: w. 350 B.C.

"Generally, about all perception, we can say that a sense is what has the power of receiving into itself the sensible forms of things without the matter, in the way in which a piece of wax takes on the impress of a signet-ring without the iron or gold; what produces the impression is a signet of ...

— Aristotle (384-322 B.C.)