The myth of the metals.
That plot of ground is their mother, and their fellow citizens are their brothers and sisters. The myth holds that each citizen has a certain sort of metal mixed in with his soul. In the souls of those most fit to rule there is gold, in those suited to be auxiliaries there is silver, and in those suited to be producers there is either bronze or iron. The city must never be ruled by someone whose soul is mixed with the wrong metal; according to an oracle, the city will be ruined if that ever happens.
The people must be told that though for the most part iron and bronze people will produce iron and bronze children, silver people silver children, and gold people gold children, that is not always the case. It is critical to observe the next generation to discover their class of soul. Those who are born to producers but seem to have the nature of a guardian or an auxiliary will be whisked away and raised with other such children. Similarly, those born to guardians or auxiliaries who seem more fit as producers will be removed to that class of society.
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