The Noble lie (n.) is a falsehood that would, in the best case, persuade even the rulers themselves.
The Noble lie (n.) cannot be made believable to its first hearers — only to their sons and later generations, once tradition carries it.
Noble lie (n.) would be this one: even if the just life were not the pleasantest, no lawgiver could tell the young a more useful falsehood than that it is.
The Noble lie (n.) tells citizens that their whole upbringing was a dream, and that they were really fashioned inside the earth, their mother, who delivered them up — so they must defend the land and treat fellow citizens as earthborn brothers.
The Noble lie (n.) is a necessary lie: Plato founded his state on one — men born with gold, silver or bronze in their bodies, castes that cannot mix; the German founds his education on a similar aeterna veritas, which would crumble before a necessary truth.